Anterior Dislocation

The vast majority of glenohumeral joint dislocations are anterior dislocations (Fig. 4-4A). This usually occurs as a result of indirect force applied to the arm in abduction, extension, and external rotation. Subcoracoid anterior dislocation is the most common subtype, followed by subglenoid, subclavicular, and intrathoracic. It is readily diagnosed on clinical exam and frontal radiographs as a medially and inferiorly located humeral head relative to the glenoid. The common associated injuries are Hill-Sachs fracture and Bankart lesion as a result of impaction of the humeral head against the glenoid during the movement of dislocation. The Hill-Sachs fracture (Fig. 4-4B) is a large defect or groove in the posterolateral aspect of the humeral head, best visualized in the internally rotated anteroposterior (AP) projection. Bankart lesions (Fig. 4-4B and C) may be composed of soft tissue (fibro-cartilaginous, cartilaginous labrum) or a piece of bone avulsed from the anteroinferior portion of the glenoid rim. They are less common than Hill-Sachs fractures. Neither one of these lesions is a sign of recurrent or previous dislocations, because they do occur at the initial dislocation.

Figure 4-4 Anterior shoulder dislocation. A, Anteroposterior radiograph of the shoulder demonstrates a classic subcoracoid anterior shoulder dislocation. The humeral head is located medial to the glenoid fossa and inferior to the corocoid process. B, Postreduction radiograph reveals an impacted fracture of the posterolateral aspect of the humeral head, consistent with a Hill-Sachs fracture (arrow). A linear lucency at the anterior glenoid rim is a bony Bankart fracture (arrowhead). C, Volumetric (3D) CT image confirms the Bankart fracture (arrowhead).

Posterior Dislocation

Posterior dislocations of the glenohumeral joint (Fig. 4-5) usually occur with violent muscle contractions, as seen with seizures, or electric shocks. The dislocation can be either subacromial, subglenoid, or subspinous. It is an uncommon injury that frequently coexists with an impacted fracture of the anterior humeral head due to trauma to the humeral head on the glenoid fossa during dislocation. It is difficult to detect clinically, especially in obese or muscular individuals. On frontal radiographs, posterior dislocations may go unrecognized in up to 50% of cases. Multiple signs have been described as helpful for detection of this subtle injury on frontal projections. The “positive rim” sign is an increase in the distance between the articular cortex of the humeral head and the anterior glenoid rim to more than 6 mm. The “light bulb” sign is a humeral head fixed in internal rotation, resembling a light bulb. The “trough line” is a curvilinear dense line parallel to the articular margin of the humeral head, representing an impacted fracture of the anterior aspect of the humeral head that coexists with the dislocation.

Figure 4-5 Posterior shoulder dislocation. A, Chest radiograph shows increased distance between the articular cortex of the humeral head and the anterior glenoid rim (double-headed arrow). Anteroposterior shoulder radiograph (B) of the same patient shows a “trough line” sign as a curvilinear density (arrowheads) consistent with an impacted reverse Hill-Sachs fracture (arrow), confirmed in the axillary projection (C, arrow).

Inferior Subluxation (Luxatio Erecta)

Luxatio erecta is a rare type of subglenoid inferior dislocation; the arm is severely hyperabducted, and the humerus is directed superiorly so that the long axis of the humeral shaft is perpendicular to the lateral chest wall. This rare entity is associated with Hill-Sachs fractures, other humeral head fractures, and occlusion of the axillary artery.

Pseudosubluxation

Pseudosubluxation describes the drooping of the humeral head with respect to the glenoid, and is usually apparent only in erect examinations. It is secondary to joint distension of traumatic or non-traumatic etiologies, for example, hemarthrosis, lipohemarthrosis, disruption of the joint capsule in chronic or recurrent dislocation, and others.

Fractures of the Proximal Humerus

The proximal humerus consists of the humeral head, anatomical neck, greater tuberosity, lesser tuberosity, surgical neck, and proximal shaft. Fractures of the proximal humerus (Box 4-8) are associated with osteoporosis. The majority of fractures are the result of indirect forces such as a fall onto an outstretched arm. Patterns of fracture and displacement are dictated by the position of the humerus at the time of injury, by bone quality, and by the direction of muscular pull on humeral fracture fragments. By counting the number of major displaced fragments and defining specific parts of involvement (head, greater tuberosity, lesser tuberosity, and shaft), Neer classified fractures of the proximal humerus into one-, two-, three-, and four-part fractures. Each of the four fracture sites results in a potential fragment, or “part.” A fragment is considered a “part” if it is displaced more than 1 cm or rotated more than 45 degrees. Regardless of the number of fracture lines, a lesser degree of displacement is considered to be minimal. One-part fractures (Fig. 4-6A) are nondisplaced or minimally displaced fractures. Muscles inserting on the proximal humerus influence the direction of fragment displacement fragments. The pectoralis major pulls the humeral shaft anteromedially. The supraspinatous and infraspinatous pull the greater tuberosity posterosuperiorly, and the subscapularis pulls the lesser tuberosity medially. When describing fractures of the proximal humerus, it is important to specify the type (one-, two-, three-, or four-part; surgical or anatomical neck) and the involved fragments (shaft, greater, lesser tuberosity). According to Neer’s description, 80% of fractures of the proximal humerus are one-part fractures and the majority of them are fractures of the surgical neck. Nondisplaced surgical neck fractures usually have a good prognosis because blood supply to the humeral head is preserved. On the contrary, fractures of the anatomical neck heal poorly because of the completely disrupted vascular supply that results in avascular necrosis and secondary osteoarthritis. Two-part fractures (Fig. 4-6B and C) account for 10% of all fractures of the proximal humerus. Displaced fractures of the surgical neck may injure the brachial plexus or axillary artery because these structures lie immediately anterior to the humeral head and surgical neck. Isolated fractures of the lesser tuberosity are unusual. A four-part fracture (Fig. 4-6D and E) is one in which the articular segment is isolated from both tuberosities and the humeral shaft. A “classic” four-part fracture is a fracture-dislocation, in which the articular segment dislocates anteriorly with no remaining soft tissue attachments. This results in an increased risk of osteonecrosis. Another important variant of a four-part fracture is the “valgus-impacted” fracture, which has a better prognosis due to maintained residual vascularity.

Figure 4-6 Fracture of the proximal humerus. A, Anteroposterior radiograph of the shoulder demonstrates a nondisplaced (“one-part”) fracture of the surgical neck of the humerus. B and C, Anteroposterior radiograph and volumetric (3D) CT reformation of the shoulder reveal a comminuted fracture of the surgical neck. This is a “two-part” fracture (proximal articulating part, and shaft): only two fragments are considered “parts” because they are displaced more than 1 cm. In addition, there is a nondisplaced fracture of the acromion process (B, arrowheads). D and E, Four-part fracture with valgus impaction is shown in an anteroposterior radiograph and a volumetric (3D) CT reformation. The greater tuberosity (G) and articulating part of the humeral head (white arrowheads) and shaft are separated from each other by more than 1 cm. The “L” indicates that this is the left shoulder.

Fractures of the Shaft of the Humerus

A humeral shaft fracture (see Box 4-8) is defined when the main fracture line is distal to the surgical neck of the proximal humerus, and proximal to the supracondylar ridge. Fractures of the humeral shaft are common. They are classified according to their location: above or below the pectoralis major insertion and above or below the deltoid insertion. Location of the fracture line affects the way the fragments are displaced. With fractures occurring above the pectoralis major insertion, the distal fragment is displaced anteromedially by the pull of the pectoralis major. Fractures occurring between the insertions of the pectoralis and deltoid muscles (Fig. 4-7) are associated with lateral displacement of the distal fragment. Fractures occurring distal to the deltoid insertion result in abduction of the proximal fragment by the deltoid and shortening of the arm by the pull of the brachialis and biceps muscles, which remain attached to the distal fragment. Associated injuries of the radial nerve are common, especially with fractures located at the junction of the mid and distal thirds. Pathologic fractures of the humerus are common in adults as a result of metastatic disease. In children, this usually occurs through a simple bone cyst of the proximal humerus.

Figure 4-7 Fracture of the shaft of the humerus. A and B, Anteroposterior and lateral radiographs demonstrate a comminuted fracture of the distal third of the humerus with a large butterfly fragment (arrows). The butterfly fragment is pulled medially and posteriorly, while the distal fragment (arrowheads) is retracted proximally due to the pull by the deltoid muscle.

The Fat Pad Sign

Normal thin layers of fat lie between the synovium and the joint capsule of the elbow anteriorly and posteriorly. In a normal flexed elbow, the anterior fat pad is visible, while the posterior fat pad is hidden in the intercondylar depression on the posterior surface of the humerus. In the presence of a joint effusion, the posterior fat pad (Fig. 4-8) becomes visible on the lateral radiograph of the flexed elbow because it is displaced posteriorly and the anterior fat pad becomes more elevated. In the acute trauma setting, elbow joint effusions can be a result of an intra-articular fracture or traumatic synovitis. This sign is usually present in children and adolescents, where 70% to 90% of patients with a posterior fat pad sign prove to have a fracture on initial or subsequent examinations. In adults, the sign is less frequently seen, and its absence cannot be used to exclude a fracture. This sign is not present in elbow dislocations, displaced intra-articular fractures with a torn joint capsule, and fracture-dislocations because it requires an intact synovium to prevent blood from mixing with extrasynovial fat. An optimal-quality lateral radiograph of the elbow is essential for evaluation of the fat pad sign. The image is taken when the elbow is flexed at 90 degrees with the hand in a lateral position. On the radiograph, three concentric arcs of the distal humerus (trochlear groove, capitellum, and medial trochlea) should be visualized.

Figure 4-8 Supracondylar fracture in children. A, Lateral radiograph of the elbow demonstrates a posterior fat pad sign (curved arrow), indicating presence of an intra-articular fracture. A subtle cortical break is seen on this view (arrow). B, Anteroposterior view confirms the fracture line (arrows).

Fractures Around the Elbow in Children

Supracondylar fractures are the most common type of fracture of the distal humerus. They are frequently seen in children aged 9 to12 years and occur as a hyperextension injury in which the olecranon acts as a fulcrum. When displaced, the fracture is easily recognized and characteristically displaced posteriorly. The brachial artery and median nerve may be stretched or interposed between fragments. Presence of abnormal cubitus valgus or varus should be assessed because either of these findings may alter the choice of therapy. Volkmann’s ischemic contracture is the most serious complication of this type of fracture and is caused by diminished blood flow to the rest of the arm. Subtle fractures are difficult to visualize directly; presence of a posterior fat pad sign and an abnormal anterior humeral line are important clues in this circumstance.

Lateral condylar fracture (Fig. 4-9) is the second most common type of fracture occurring around the elbow in children. This fracture is caused by a lateral blow to the forearm, resulting in varus stress across the elbow. Typically, the fracture line runs across or along the physis, with or without a small metaphyseal fragment. Fractures may terminate in the physis (incomplete) or extend beyond the physis through the ossified capitellum or unossified cartilage (complete). Differentiation between incomplete and complete fractures can be difficult because most of the fractures extend through the unossified cartilage. Additional imaging with magnetic resonance imaging (MRI) or intraoperative assessment with arthrography is often needed.

Figure 4-9 Lateral condylar fracture in children. Anteroposterior and lateral radiographs (A and B, respectively) of the elbow demonstrate a displaced lateral condylar fracture (arrows), which is the second most common fracture around the elbow in children.

Fractures of the Distal Humerus

The distal humerus consists of two columns of medial and lateral epicondylar ridges located at the distal humeral metaphysis and a central articulating axis (trochlea). The most distal part of the lateral column is the capitellum, and that of the medial column is the nonarticular medial epicondyle. Between the two columns lies the trochlea, which serves as a “tie-arch.” Although the column anatomy is not important for stability of the elbow, it is essential for determining the type of surgical reconstruction. An increasing trend toward operative treatment of these fractures requires a more comprehensive classification system. The AO/OTA (Orthopedic Trauma Association) classified distal humeral fractures into three types. Type A is an extra-articular fracture, type B is a partial articular fracture, and type C is a complete articular fracture. Ninety-five percent of distal humeral fractures in adults are intra-articular.

Type A extra-articular fractures (Fig. 4-10A and B) include apophyseal avulsion fractures (avulsion of the lateral epicondyle, medial epicondyle) and simple and complex nonarticular metaphyseal transcolumn fractures. Type B partial articular fractures (Fig. 4-10C and D) are intra-articular fractures that involve only one column (either medial or lateral) with one or more sites of intra-articular extension (capitellum, trochlea, or both). They are subtyped into lateral sagittal fractures, medial sagittal fractures, and frontal fractures. Sagittal fractures are either transcapitellar or transtrochlear fractures depending on the fracture line involvement. Frontal fractures are isolated fractures of the capitellum, trochlea, or both, without metaphyseal extension. Fractures of the capitellum account for 10% of all distal humeral fractures in adults. A shearing force transmitted by the radial head or trochlear groove results in this type of injury. The fragment is visualized on the lateral radiograph of the elbow and is characteristically displaced proximally above the radial head and coronoid process.

Figure 4-10 Fractures of distal humerus. A and B, Anteroposterior and lateral radiographs of the elbow show a comminuted transverse extra-articular metaphyseal fracture (type A) (arrows) with medial and volar displacement of the distal fragment. C and D, Transtrochlear fracture (partial articular, type B) (arrows) with mild displacement. The fracture extends from the trochlea to the lateral column of the distal humerus. E and F, Complete articular fracture (type C) with marked displacement. The fracture lines extend to both medial and lateral columns (arrows) of the distal humerus, as well as to the articular surface of the elbow (arrowhead). Distinction between type B and type C is based on the number of columns involved.

Type C, complete articular fractures (Fig. 4-10E and F), are fractures that involve both the medial and lateral columns, with articular extension. These fractures are further subclassified according to the nature (simple or complex) of the column fracture and the presence of intra-articular extension.

Fractures of the Proximal Radius

A radial head fracture (Fig. 4-11A and B) is the most common elbow injury in adults. It is intra-articular and usually produces hemarthrosis. It can be very subtle due to minimal cortical disruption and is usually not seen on all projections. Two patterns of fractures are usually seen: a single longitudinal fracture through the proximal articular surface, and impaction of the intact radial head into the radial neck. The former presents as a step-off or abrupt angulation of the joint surface, or depression of the fragment (double line of cortical bone). The latter creates an abrupt step-off between the normally gentle concave curve of the radial head and neck. Three types of radial head fractures were described by Mason, and later modified by Morrey to include a type IV fracture. Type I is a nondisplaced fracture, which accounts for 50% of cases. Type II is a displaced fracture without comminution, and type III is a comminuted fracture. Type IV is a radial head fracture-dislocation. The fracture is considered displaced if a fragment involves 30% or more of the articular surface and is displaced more than 2 mm. Open reduction with internal fixation is sometimes used to correct this fracture, especially with a large displaced fragment.

Figure 4-11 Fractures of the radial head and olecranon process. A, Lateral radiograph of the elbow demonstrates a classic posterior fat pad sign (arrows) produced by posterior bulge of the extrasynovial fat. In addition, there is an elevated anterior fat pad (white arrowheads). The cause of the joint effusion is a radial head fracture (black arrowhead). B, The black arrowhead demonstrates a nondisplaced fracture of the radial head. C, Lateral radiograph of the elbow shows a transverse fracture of the olecranon process (black arrowhead), a posterior fat pad sign (arrows), and elevated anterior fat pad (white arrowheads).

Presence of comminuted radial head and neck fractures due to high-energy trauma should raise suspicion for additional elbow and forearm injuries, such as capitellar and coronoid process fractures, elbow dislocation, and the Essex-Lopresti fracture. The latter consists of an unstable, comminuted fracture of the radial head and neck, and proximal migration or subluxation of the distal radioulnar joint that leads to an acute tear of the interosseous ligament of the forearm. Fractures of the olecranon (Fig. 4-11C) are the second most common type of elbow fractures in adults. They can be caused by a direct injury to the olecranon itself, which usually presents with comminution and distracted fragments, or by an indirect injury (e.g., a fall on the forearm) that results in simple fractures. If the periosteum is completely torn, traction by the triceps will displace the proximal fragment proximally resulting in a wide fracture gap. Although the fractures are usually obvious on lateral radiographs, soft tissue swelling in the olecranon bursa is an important clue to the presence of a subtle fracture.

Fractures of the coronoid process (Fig. 4-12) are usually oriented in the coronal plane and are caused by a shearing mechanism, most commonly from a posterior elbow dislocation. These fractures are pathognomonic of an episode of elbow instability. In every posterior dislocation, the coronoid process should be examined closely to exclude a fracture. A free intra-articular bone fragment within the elbow joint of an adult with posterior dislocation is most likely a displaced coronoid process fracture.

Figure 4-12 Elbow dislocation and fracture of the coronoid process. Lateral radiograph of the elbow demonstrates a posterior dislocation of the radius and ulna with respect to the distal humerus. A coronoid process fracture is noted (arrowheads).

Dislocations of the Elbow

The elbow is one of the most commonly dislocated joints of the body. Elbow dislocations usually occur in young people, with a peak in individuals between 5 and 25 years of age. Dislocations of both the radius and ulna, with respect to the distal end of the humerus, are the most frequently seen type. More than 80% are posterior or posterolateral dislocations (see Fig. 4-12). Less commonly, the radius and ulna dislocate in divergent directions. Common associated injuries include fractures of the coronoid process, radial head, and medial epicondyle of the humerus. “Terrible triad” fracture-dislocations describe the combination of elbow dislocation with radial head and coronoid process fractures. This condition is prone to early recurrent instability and post-traumatic arthritis.

Abnormal Pronator Quadratus Sign

The pronator quadratus is a thin flat muscle located on the volar aspect of the interosseous membrane at the level of the distal radioulnar joint. It is normally seen on lateral radiographs, outlined by a thin radiolucent fat stripe. When there is hemorrhage beneath the muscle, the contour of the muscle bulges anteriorly. This could present as a volar bulge of the thin fat stripe superficial to the muscle, or as a loss of definition of the lucent fat stripe overlying the muscle itself. It is usually caused by injuries to the distal third of the radius and ulna.

Monteggia Fracture-Dislocation

Monteggia fracture-dislocation is a combination of a fracture of the proximal ulnar shaft and subluxation or dislocation of the radial head. The term “Monteggia lesion” describes a number of traumatic lesions that have in common disruption of the radial head and fracture of the ulna at any level. Four types of Monteggia fracture-dislocation (Bado classification) are described according to the direction of the displaced ulnar fracture and the dislocated radial head. Type I is the most common; it is a fracture-dislocation with volar angulation at the fracture site and volar dislocation of the radial head. Type II, or reverse Monteggia fracture-dislocation (Fig. 4-13), is more likely to be seen in adults. This type has dorsal angulation at the fracture site and dorsal dislocation of the radial head. Type III is the most severe of all Monteggia fracture-dislocations. The fracture fragments are laterally displaced, with lateral or anterolateral dislocation of the radial head. Type IV is a fracture-dislocation that includes fractures of the proximal radius and proximal ulna along with volar dislocation of the radial head. In the presence of an isolated fracture of the shaft of a forearm bone, one must always anticipate the possibility of injuries to other bones.

Figure 4-13 Monteggia fracture-dislocation. A, Lateral radiograph of the forearm demonstrates dorsal dislocation of the radial head (black arrowheads), along with an angulated comminuted fracture of the proximal third of the ulna (arrows). Soft tissue gas indicates an open injury. This is a type II Monteggia fracture-dislocation. B, Volumetric (3D) CT reformation reveals an impacted fracture of the radial head (white arrowhead) along with the Monteggia fracture-dislocation.

Galeazzi Fracture-Dislocation

Galeazzi fracture-dislocations (Fig. 4-14) are uncommon, accounting for 3% to 6% of all forearm fractures. They consist of a fracture of the distal third of the radial shaft and dislocation or subluxation of the distal radioulnar joint (DRUJ). When one is faced with an isolated radial shaft fracture, injury of the DRUJ should be sought. The following signs suggest traumatic disruption of the DRUJ: fracture of the ulnar styloid at its base, widened DRUJ space on a frontal radiograph, dislocation of the radius relative to the ulna on a lateral radiograph, and radial foreshortening.

Figure 4-14 Galeazzi fracture-dislocation. A and B, Lateral and anteroposterior radiographs of the forearm show a displaced transverse fracture of the radial shaft at the junction of the middle and distal thirds, along with dislocation of the distal radioulnar joint (DRUJ). Dislocation of the radius relative to the ulna on the lateral radiograph and radial foreshortening (double-headed arrow) are clues suggesting DRUJ disruption.

Fractures of the Distal Radius

Fractures of the distal radius are exceedingly common and usually the result of low-energy trauma. They affect women more than men and their incidence increases with advancing age. Although the classification of these fractures as Colles’, Smith, or Barton types continues to be used in practice, most distal radial fractures do not fall into one of these categories. The more clinically useful way to describe the fractures of the distal radius is to use the number of fracture “parts” and to define whether the fracture is intra- or extra-articular. Extra-articular fractures do not affect either the radiocarpal joint or the DRUJ. They characteristically occur in the distal 3 to 4 cm of the radius and are composed of two parts. Intra-articular fractures can have two, three, four, or more parts. They extend into the radiocarpal joint or DRUJ. Barton and Chauffeur’s fractures fall into this category. The degree of intra-articular incongruity is the most clinically significant predictor of functional outcome and future degenerative changes of the radiocarpal joint, especially if there are 2 mm or more incongruity. Stability of these fractures is determined by the degree of angulation, comminution of the dorsal metaphysis, presence of intra-articular extension, and the patient’s age.

Colles’ fracture (Fig. 4-15A and B) is a transverse extra-articular fracture of the distal radius with dorsal displacement of the distal fragment along with the bones of the wrist and hand. It usually occurs as a result of a fall on the outstretched hand. It is commonly associated with an ulnar styloid process avulsion fracture, scapholunate dissociation, and other carpal dislocations or fractures.

Figure 4-15 Fractures of the distal radius. A and B, Posteroanterior and lateral wrist radiographs demonstrate a transverse extra-articular fracture of the distal end of the radius (arrows) with dorsal displacement of the distal fracture fragment, producing a “dinner fork” deformity. This is a classic Colles’ fracture. C and D, Smith, or reverse Colles’, fracture is demonstrated and characterized by volar displacement of the distal fracture fragment.

Fractures of the ulnar styloid occur in approximately 60% to 70% of distal radial fractures. The majority of them are small avulsions involving the tip of the ulnar styloid. Choice of treatment remains controversial, although the injury may well produce symptoms owing to the fracture itself or to associated injury to the triangular fibrocartilage complex. Treatment may be indicated if the fracture involves the base of the ulnar styloid with significant displacement and/or gross translation of the radius relative to the ulna.

The Smith fracture (Fig. 4-15C and D) is a transverse fracture of the distal radius with volar displacement of the distal fragment together with the carpus and hand; therefore the term “reverse Colles’ fracture” has been used.

The Barton fracture (Fig. 4-16A and B) is an oblique coronal fracture of the dorsal or volar margins of the distal radius with intra-articular extension. If the fracture line extends to the volar aspect of the distal radius, it is called a volar Barton fracture. The volar Barton fracture is more common than its counterpart, the dorsal Barton fracture, in which the fracture line extends to the dorsal aspect of the distal radius.

Figure 4-16 Fractures of the distal radius. A and B, Frontal and lateral radiographs of the wrist demonstrate an oblique coronal fracture of the distal radius with intra-articular extension. The fracture line extends to the volar aspect of the distal radius (volar Barton fracture). C, Frontal radiograph of the wrist shows a nondisplaced transverse fracture of the radial styloid process, or a Chauffeur’s fracture. D and E, Torus fracture. Posteroanterior and lateral radiographs of the wrist of a child reveal a subtle undulation in the distal radial metaphysis (arrows). This is a classic location for a fracture of the dorsal cortex of the distal radial metaphysis.

Chauffeur’s fracture (Hutchinson fracture) (Fig. 4-16C) is an intra-articular fracture of the base of the radial styloid process. The name comes from the era when hand cranking was needed to start motor vehicles. At present, it is most frequently caused by a fall on an outstretched hand, resulting in an avulsion of the radial collateral ligament, or a direct blow to the radial styloid process.

Torus fracture (buckle fracture) (Fig. 4-16D and E) is the most common fracture of the distal forearm in young children. It is usually caused by a fall on an outstretched hand. Characteristically, the fracture involves only one side of the cortex on the compression side, usually 2 to 3 cm proximal to the physis. The periosteum and cortex are intact on the side opposite to the fracture, hence this fracture has a good prognosis.

Scaphoid Fracture

Scaphoid fractures (Fig. 4-17) are the most common fractures of the carpal bones. They occur almost exclusively in young adults due to a fall on an outstretched hand, athletic injuries, or motor vehicle accidents. A strong index of suspicion is the key to early diagnosis, because scaphoid fractures may produce only limited motion with little pain or swelling. Although a series of four radiographic views of the wrist is usually sufficient for diagnosis, up to 30% of scaphoid fractures are radiographically occult. Presence of “snuffbox” tenderness and a history of trauma, even with negative radiographs, necessitates immobilization or further imaging with CT or MRI. If immobilization is used, obtaining follow-up radiographs after 10 days usually reveals abnormalities, with either resorption of the fracture line (clearly visible lucent line) or faint sclerosis around the fracture. MRI is the current gold standard for diagnosis of wrist injuries. By excluding a fracture, MRI can eliminate the need for prolonged immobilization. CT is becoming a more common investigation in acute wrist trauma because of its widespread availability and short scan time. Scaphoid fractures are classified based on their anatomic location: proximal third (proximal pole), middle third (waist), distal articulating portion, and tubercle. The most common location is at the waist (80%), followed by the proximal pole (15%), tubercle (4%), and distal articular portion (1%). Location of the fracture determines prognosis because of the characteristic blood supply to the scaphoid. The scaphoid is supplied by two major vascular pedicles. One enters the tubercle, supplies the distal third, and accounts for 20% to 30% of the blood flow. The second one enters a foramen on the spiral groove at the waist and provides 70% to 80% of the blood supply in a retrograde fashion: from the waist to the proximal pole. The more proximal the fracture line, the greater the incidence of avascular necrosis. Stability of the fracture depends on the presence of displacement, degree of comminution, and associated injuries.

Figure 4-17 Scaphoid fracture. A, Posteroanterior radiograph of the wrist in ulnar deviation reveals a subtle cortical disruption at the waist of the scaphoid (curved arrow). B, Coronal reformatted CT image of the same patient performed subsequently confirms a scaphoid fracture (arrow). C, In a different patient, a coronal T1-weighted MR image reveals a scaphoid waist fracture (arrow). There is T1 hypointensity in the proximal pole of the scaphoid (arrowhead), indicating development of avascular necrosis in this nonacute fracture.

Triquetral Fracture

Triquetral fractures (Fig. 4-18A and B) are the second most common fractures of the carpal bones. They commonly involve the dorsal surface, as a result of a shear or chisel injury from impingement of the ulnar styloid on the dorsal aspect of the triquetrum when the wrist is forcibly dorsiflexed and ulnarly deviated. Pain and tenderness are localized to the dorsolateral portion of the wrist. A flake of bone fragment is best visualized in the lateral or pronated oblique projections. A transverse fracture of the triquetral body is easily identified on a standard posteroanterior view. However, CT may be required to determine the extent of injury.

Figure 4-18 Other carpal fractures. A and B, Lateral radiograph of the wrist and sagittal reformatted CT image, respectively, demonstrate a small dorsal triquetral fracture (arrows) with overlying soft tissue swelling. C, Hook of hamate fracture. Axial CT image shows a nondisplaced fracture of the hook of the hamate.

Hamate Fracture

Fractures of the hamate (Fig. 4-18C) are rare and frequently missed on radiographs. They can involve the body or the hook of the hamate. The latter is more common and can produce significant disability. Either a direct blow to the hook or an avulsion of the transverse carpal ligament and pisohamate ligaments can cause this fracture. It is best visualized on a carpal tunnel view or on CT scan. Absence or indistinctness of the “eye” sign (an oval, dense, cortical ring shadow over the hamate) is a finding that suggests a fracture of the hook of the hamate on frontal radiographs.

Lunate Fracture

The lunate is the fourth most commonly fractured carpal bone, after the scaphoid, triquetrum, and trapezium. Most patients have a hyperextension injury, or repetitive stress of the wrist. Isolated acute lunate fractures are frequently unrecognized on radiographs because of lack of displacement and superimposed structures. CT and MRI provide more precise detail and accurate diagnosis. Fragmentation of the lunate occurs in Kienbock’s disease (idiopathic avascular osteonecrosis of the lunate). This condition is sometimes confused with lunate fractures. Multiple causes predispose to Kienbock’s disease: primary fracture, repetitive trauma, injury to the ligament carrying blood to the lunate, and presence of ulnar negative variance. In an early stage, the lunate may appear normal on radiographs. Later on, sclerosis, loss of lunate height, fragmentation, and eventually wrist collapse and arthritis ensue.

Carpal Dislocations

The mechanism responsible for most carpal dislocations is an axial compression-hyperextension injury usually from a fall onto the outstretched hand. Failure of the connecting structures bridging the proximal and distal rows of the carpus results in dorsal displacement of the distal row (perilunate dislocation). If the force is more severe, a complete lunate dislocation may occur. These injuries are easily diagnosed on lateral radiographs. Perilunate dislocation (Fig. 4-19A and B) is the most common type of wrist dislocation. There is a dorsal dislocation of the carpal bones (scaphoid, triquetrum, and other carpal bones) about the lunate, while the lunate itself remains in normal position with respect to the distal radius. Loss of congruity of the three carpal arcs and an abnormal triangular configuration of the lunate with the apex pointing distally are signs on frontal radiographs. On the lateral projection, there is a normal relationship of the lunate and distal radius, but all other carpal bones are located posterior to the lunate. When it occurs in association with a scaphoid waist fracture, it is called a transscaphoid perilunate dislocation.

Figure 4-19 Carpal dislocations and instabilities. A and B, Perilunate dislocation. Posteroanterior radiograph (A) of the wrist shows a wide scapholunate space, loss of congruity of the three carpal arcs, and triangular configuration of the lunate (L). Lateral radiograph (B) confirms dislocation of the carpal bones (curved arrow) with the lunate (L) remaining in normal position with respect to the distal radius. C and D, Lunate dislocation. Lateral view (D) demonstrates a dislocated lunate (L) with respect to the distal radius and other carpal bones, giving the appearance of a “spilled teacup” (curved arrow). E, Scapholunate dissociation is shown as widening of the scapholunate space (arrow) to more than 5 mm (“Terry Thomas” sign).

In lunate dislocation (Fig. 4-19C and D), the lunate is dislocated volarly with respect to the distal radius, and all other carpal bones lie dorsal to the lunate. This produces a radiographic “spilled teacup” sign on the lateral radiograph. The capitate migrates proximally and sits in the lunate fossa. On the frontal projection, the congruity of the three carpal arcs is lost, and there is superimposition of the base of the capitate and lunate. Lunate dislocations commonly occur in association with scaphoid fractures.

Carpal Instabilities

The radiographic signs of carpal instabilities include disruption of one or all of the three carpal arcs (arcs of Gilula), alteration of the symmetrical intercarpal joint spaces, and changes in contour of an individual carpal bone.

Scapholunate dissociation, or rotatory subluxation of the scaphoid (Fig. 4-19E), is a spectrum of injuries caused by interruption of the scapholunate ligament and extrinsic ligaments that stabilize this articulation, resulting in abnormal motion between the scaphoid and lunate. It is the most common pattern of carpal instability. Due to the normal compressive forces across the wrist, which tend to force the scaphoid into further palmar flexion, disruption of the scapholunate ligament seen in scapholunate dissociation will allow an abnormal degree of palmar flexion of the scaphoid. Thus, the key finding on the lateral radiograph is an increased scapholunate angle of more than 60 degrees. On frontal radiographs, there is a widening of the scapholunate space of more than 3 mm measured at or distal to the midpoint of the joint space (5 mm is considered to be pathognomonic); this is called the “Terry Thomas” sign. If in doubt, comparison between the scapholunate space and lunotriquetral space should reveal a significant widening of the former in the case of scapholunate dissociation. The “cortical ring” sign is another radiographic finding of this condition, describing the cortex of the distal pole of the palmar-flexed scaphoid seen end-on on the frontal radiograph. This type of injury can be isolated or associated with distal radial fractures. Without treatment, it may lead to scapholunate advanced collapse.

Dorsal intercalated segmental instability (DISI, or dorsiflexion instability) is usually associated with scapholunate dissociation. It is a derangement of the radial side of the wrist and is often associated with radial-sided symptoms. On a lateral radiograph, the lunate tilts dorsally, resulting in an increased capitolunate angle of greater than 20 or 30 degrees. Lateral fluoroscopy of the wrist in flexion is more definitive, as the static radiographic configuration of DISI can occasionally be seen as a normal variant. DISI is most frequently observed with displaced scaphoid fractures and scapholunate dissociation.

Volar intercalated segmental instability (VISI, or volar flexion instability) is much less common than DISI, although it is the most common pattern of carpal instability seen in patients with rheumatoid arthritis. It is a result of ulnar-sided ligament derangement. The lunate tilts volarly and the capitolunate angle is greater than 20 or 30 degrees.

First Metacarpal (Thumb) Fractures and Dislocations

Fractures of the base of the first metacarpal account for 80% of thumb fractures. They usually result from an axial load to the partially flexed first metacarpal. Four types include epibasal (extra-articular) (Fig. 4-20A), Bennett, Rolando, and comminuted fractures. Bennett fractures (Fig. 4-20B) are intra-articular oblique fractures through the proximal articular surface of the first metacarpal, usually in two separate fragments. Due to traction by the abductor pollicis tendon, which inserts on the dorsal surface of this metacarpal, the large distal fragment together with the rest of the thumb is retracted proximally. Rolando fractures (Fig. 4-20C) are intra-articular comminuted fractures consisting of three major fragments. In Rolando and comminuted fractures (Fig. 4-20D), instead of being retracted, the large distal fragment is impacted into the two smaller fragments.

Figure 4-20 Fractures of the base of the first metacarpal. Four types of fractures (arrows) are shown. A, Epibasal extra-articular type. B, Bennett, or intra-articular oblique fracture, with two separate fragments. C, Rolando fracture, a comminuted fracture with three separate fragments. D, Comminuted fracture.

Gamekeeper’s or skier’s thumb (Fig. 4-21) signifies the injury to the ulnar collateral ligament of the first metacarpophalangeal joint owing to forceful abduction of the first proximal phalanx. The spectrum of injuries ranges from a pure ligamentous injury to an avulsion of the ulnar aspect of the distal attachment site of the ligament or a transverse fracture of the base of the proximal phalanx.

Figure 4-21 Gamekeeper’s or skier’s thumb. Avulsion fracture (curved arrow) of the ulnar aspect of the base of the proximal phalanx of the thumb.

Dislocations of the Carpometacarpal Joints

A very complex network of dense carpometacarpal and intermetacarpal ligaments holds the carpometacarpal (CMC) joints together. Therefore, it requires a major force to cause injuries to this region. Dislocation at the first CMC joint usually occurs with high-energy trauma, with concomitant neurovascular injuries. Pure thumb CMC dislocation is mostly dorsal and results from axial loading on a partially flexed thumb. Of the other CMC joints, fractures and dislocations frequently occur at the fourth and fifth CMC joints (Fig. 4-22) because of their greater flexibility and mobility.

Figure 4-22 Carpometacarpal dislocation. A, Posteroanterior radiograph of the hand demonstrates a subtle overlap (arrow) of the proximal end of the fifth metacarpal and the hamate. B, Lateral radiograph reveals dorsal dislocation of the fifth metacarpal (black arrowheads) with respect to the carpal bones (white arrowheads). A fracture of the body of the hamate is also visualized (arrow).

Metacarpal Fractures

Fractures of the metacarpal bones are classified according to their location; base, shaft, neck, or head. They are commonly oblique or spiral, rather than transverse, in configuration, and are usually obvious. The exception is a nondisplaced fracture at the base of the lateral metacarpal bones, which is frequently occult because of the bony configuration, superimposition in this region, and minimal displacement of fragments. Boxer’s fracture (Fig. 4-23) is a metacarpal neck fracture with volar angulation of the distal fragment as a result of a direct impact on the metacarpal head with a clenched fist. It is most commonly seen in the fifth metacarpal. The description of boxer’s fracture is somewhat misleading since professional fighters are more likely to sustain a second or third metacarpal neck fracture. Fractures of the base of the metacarpals are divided into four types: epibasal, two-part (reverse Bennett), three-part, and comminuted. In the reverse Bennett type, the flexor and extensor carpi ulnaris muscles usually retract the larger distal fragment proximally.

Figure 4-23 Boxer’s fracture. A posteroanterior radiograph of the hand demonstrates a metacarpal neck fracture (arrow) with volar angulation of the distal fragment.

Dislocations of the Metacarpophalangeal Joints

The most common type of metacarpophalangeal (MCP) joint dislocation is dorsal dislocation. Volar dislocation is rare, but potentially unstable. When a fracture is clinically irreducible, it is called a complex dislocation that is most often due to volar plate interposition. A radiographic sign of complex dislocation is the appearance of a small piece of bone in the joint space representing an interposed volar plate.

Phalangeal Fractures

Phalangeal fractures are more common than metacarpal bone fractures. They may be classified as either extra-articular (involving the shaft) or intra-articular (involving the proximal or distal margins). The distal phalanx is most commonly involved, accounting for more than half of hand fractures. They vary from a comminuted, longitudinal split to a transverse fracture, and frequently are associated with lacerations of the nail bed. Fractures of the proximal phalanx (P1), middle phalanx (P2), and distal phalanx (P3) (Fig. 4-24) are described according to their location (head, neck, shaft, and base) and appearance. Baseball or mallet finger (Fig. 4-25A) is a flexion deformity at the distal interphalangeal (DIP) joint due to an avulsion of the extensor tendon at its insertion on the dorsal lip at the base of the distal phalanx. The injury occurs when an extended DIP joint is forcibly flexed, as occurs when the finger is jammed by a baseball striking the tip of the finger. A small piece of bone may or may not be avulsed along with the tendon. Radiographs may reveal no fracture but only flexion deformity of the DIP joint.

Figure 4-24 Transverse fracture of the distal phalanx. This fracture is commonly associated with nail bed injuries.

Figure 4-25 Fractures and dislocations involving the interphalangeal joint. A, Mallet finger. Lateral radiograph of the finger shows an avulsion fracture (arrow) at the dorsal lip of the base of the distal phalanx, resulting in flexion deformity of the distal interphalangeal joint. B, Volar plate fracture. Lateral radiograph of the finger demonstrates an avulsion fracture of the volar lip of the base of the middle phalanx.

Jersey finger is an avulsion of the flexor digitorum profundus tendon from its insertion at the volar base of the distal phalanx. It is caused by forced extension while in flexion of the DIP joint, such as when grabbing a jersey of a football player. It is similar to the volar plate injury.

Volar plate injury (Fig. 4-25B) is an avulsion injury at the insertion of the volar plate on the volar surface of the base of the middle phalanx at the proximal interphalangeal (PIP) joint. It is a hyperextension injury that can occur with or without bony avulsion. In the latter, a small avulsed bone fragment is usually nondisplaced. The fragment is often a thin sliver of bone, minute and easily overlooked. It is best visualized on lateral or oblique projections of the involved finger.

Boutonniere deformity is a flexion deformity of the PIP joint with hyperextension of the DIP joint. It is caused by a tear or avulsion of the middle slip of the extensor mechanism that allows the PIP joint to flex while the DIP is extended. The site of avulsion is on the dorsal surface of the base of the middle phalanx. At the time of the initial injury, the patient may complain only of pain and swelling about the PIP joint. The characteristic deformity develops subsequently.

Dislocations of the Interphalangeal Joints

Dislocations of the interphalangeal joints are a result of hyperextension injury. Most of these are dorsal dislocations in which the affected phalanx is displaced dorsally. They are associated with a volar plate rupture that manifests as an avulsion with or without a small flake of bone from the volar margin of the base of the phalanx. Irreducible dorsal dislocations are most often due to a trapped volar plate, trapped flexor digitorum profundus tendon, or a buttonholed middle phalanx through the volar plate or a rent in the flexor digitorum profundus tendon. On rare occasions, an irreducible dislocation is caused by interposition of a sesamoid bone within the joint.

Isolated Injuries Without Disruption of the Pelvic Ring

Avulsion injuries (Fig. 4-26) are secondary to sudden muscular contractions or abrupt changes of speed or direction, as seen during athletic activities. They are frequent in adolescents before closure of the apophyses because the muscles and tendons are stronger than the apophyseal attachments. Typical locations are at the anterior superior iliac spine (Sartorius), anterior inferior iliac spine (rectus femoris), ischial tuberosity (biceps femoris), and inferior margin of the pubic body (adductor group). The fractures are displaced due to the mechanical pull by the muscles and are usually obvious on radiographs at the initial injury. The contour of the displaced fragment mirrors the adjacent (donor) portion of the pelvis. These injuries, if not detected at the initial presentation, may heal with exuberant callus and radiographically mimic bone tumors.

Figure 4-26 Pelvic fracture without pelvic ring disruption. Anteroposterior radiograph of the pelvis demonstrates an avulsed right anterior superior iliac spine (arrows) due to a sudden muscular contraction of the sartorius. Arrowheads indicate the donor site.

Isolated fractures of the pelvic bones that do not disrupt the pelvic ring include fractures of the iliac wing (Duverney fracture) and transverse fractures of the lower sacral and coccygeal segments. Sacrococcygeal dislocations and coccygeal fractures are in this category.

Pelvic Ring Disruption

The most common mechanism causing a fracture with pelvic ring disruption is a motor vehicle accident. Depending on the Injury Severity Score and age of the patient, it is associated with a high mortality rate of 5% to 50%. Interruption of the pelvic ring at two or more sites on opposite sides, either by fractures or diastasis, indicates a potentially unstable injury. The rule of thumb is that a disruption at one site of the pelvic ring must accompany another on the contralateral side of the ring. Therefore, when one encounters a pelvic ring disruption, a fracture or separation of the contralateral side of the ring must be carefully searched for. The exceptions to this rule are pediatric patients before fusion of the triradiate cartilage and stress or insufficiency fractures. It should be noted that acetabular fractures do not constitute any component of pelvic ring disruption. Classification schemes are helpful in defining the injuries, allowing optimal communication, and assisting in treatment planning. However, their ability to predict associated injuries, morbidity, or mortality has not been rigorously tested.

The most widely accepted classification of pelvic ring disruption is the Young-Burgess system. This system divides pelvic ring disruptions into four types according to the direction of forces to the pelvis: lateral compression (LC), anteroposterior compression (APC), vertical shear (VS), and combined mechanism (CM). In the LC category (Fig. 4-27A) are the transverse fractures of the pubic rami with ipsilateral or contralateral posterior ring injuries. In the APC category (Fig. 4-27B and C), there is a symphyseal diastasis or longitudinal fracture of the pubic rami and a disruption of the sacroiliac joint. In the VS category (Fig. 4-27D), there is vertical displacement anteriorly through a symphyseal diastasis and posteriorly through the sacroiliac joints, or, occasionally, the iliac wing or sacrum. The most common pattern of combined mechanism is a combined LC/VS injury.

Figure 4-27 Pelvic fractures with pelvic ring disruption. A, A volumetric (3D) CT reformation demonstrates a lateral compression (LC) type of pelvic ring disruption. Vertical fractures of the left superior and inferior pubic rami (anterior ring disruption, white arrowheads) with overlap of medial and lateral fragments are shown. There is a vertical fracture of the left ala of the sacrum through its neural foramina (black arrows). B and C, Anteroposterior compression. Anteroposterior radiograph of the pelvis (B) and axial CT image (C) at the level of the mid-sacrum demonstrate diastasis of the symphysis pubis (anterior ring disruption, arrows). The radiograph fails to provide information about a posterior ring abnormality. Axial CT image reveals mild widening of the right sacroiliac joint, indicating an injury to the posterior ring. D, Vertical shear. Anteroposterior radiograph of the pelvis demonstrates diastasis of the pubic symphysis (anterior ring disruption) and vertical fracture of the right iliac wing involving the pelvic inlet (posterior ring disruption). There is vertical displacement, with foreshortening, of the whole right lower extremity, indicating a vertical shear injury.

Common terms previously used to describe pelvic ring disruption include Malgaigne injury, bucket-handle injury, and open book injury. Malgaigne injury is a vertical shear injury that results in disruption of the ipsilateral anterior and posterior arches. There is superior displacement of the involved hemipelvis with respect to the opposite side, resulting in clinically visible shortening of that extremity. Bucket-handle injury is a disruption of the contralateral anterior and posterior arches. Open book injury describes an anteroposterior compression mechanism that results in a pubic diastasis along with lateral rotation of the hemipelvis due to posterior arch disruption (classically, sacroiliac diastasis).

Determination of the stability of pelvic fractures relies mainly on clinical grounds. In general, a single break in the pelvic ring is a stable injury (e.g., single pubic ramus, unilateral pubic rami, Duverney fracture, transverse sacral fracture), and two or more breaks in the pelvic ring are considered unstable. It should be noted that the initial radiographic exams might not demonstrate instability when the pelvis is indeed unstable.

Sacral Fractures

The majority of sacral fractures are associated with pelvic or lumbar spine fractures. They are frequently oriented in the vertical plane (only 5% to 10% are transverse). The Denis classification divides the sacrum into three zones and describes the risk of neurological deficits associated with fractures in each zone. Zone I (Fig. 4-28A) is located lateral to the sacral foramina, and fractures rarely cause neurological deficit. Zone II fractures (Fig. 4-28B) occur through the sacral foramina (transforaminal); there is an approximately 28% chance of neurological deficit. Zone III fractures involve the central canal and carry a 57% risk of neurological deficit.

Figure 4-28 Sacral fractures. A, Zone I injury. Axial CT image at the level of the mid-sacrum demonstrates a subtle irregularity of the anterior cortex of the right sacral wing, indicating a nondisplaced fracture (white arrow). The fracture is located lateral to the sacral neural foramina. B, Zone II injury. Anteroposterior radiograph of the pelvis shows abnormal disrupted concavities of multiple left sacral neural foramina, indicating a vertical fracture (arrowheads).

Associated Pelvic Injuries

Pelvic hemorrhage is the primary concern in patients with pelvic ring disruption. To reduce the risk of bleeding, patient manipulation and movement should be restricted until conditions are stabilized. Therefore, the initial radiographic exams are restricted to the AP view of the pelvis (and/or outlet view, CT scan). Urinary tract injury is more common with specific types of pelvic fractures, such as symphyseal diastasis and pubic rami fractures. Clinically, gross hematuria is the most obvious sign of urinary tract injury associated with pelvic fractures. The presence of microscopic hematuria is rarely associated with a urinary tract injury requiring surgical intervention. If indicated, complete evaluation of the urinary tract requires CT, cystography (conventional or CT), and urethrography. Direct injury to the gastrointestinal tract is usually caused by fracture fragments lacerating the anus or rectum. The injury often extends to the perineum. For a more complete discussion of associated injuries in pelvic fractures please refer to chapters Chapters 3, 7, and 11.

Posterior Wall Fractures

Posterior wall fractures (Fig. 4-29C) are the most common type of acetabular fractures, accounting for one third of them. There is disruption of a variable amount of the posterior wall of the acetabulum. The fracture may have one single fragment or multiple fragments, the latter being more common.

Transverse Fractures

The transverse fracture line (Fig. 4-29D) separates the innominate bone and acetabulum into two segments: a superior iliac segment and an ischiopubic segment containing both rami. It disrupts both the iliopectineal and ilioischial lines and crosses the acetabulum horizontally or obliquely. Its frequency ranges from 5% to 19% of all acetabular fractures.

Transverse Plus Posterior Wall Fractures

A combination of transverse and posterior wall fractures accounts for 20% of all acetabular fractures. In up to 96% of cases there are associated hip dislocations.

Associated Both Column Fractures

ABC fractures are the most common associated-type fractures of the acetabulum and the second most common (23%) overall. There is no portion of the articular surface of the acetabulum remaining in contact with the innominate bone, and there is a split between the anterior and posterior column components. The “spur” sign represents an external cortex of the most caudal portion of the intact ilium. It is visualized because the femoral head is displaced medially along with all portions of the acetabular surface. This sign is pathognomonic for an ABC fracture and is best demonstrated on the Judet’s obturator oblique projection.

T-Shaped Fractures

These fractures represent 7% of all acetabular fractures. There is a transverse fracture with an associated vertical fracture line running across the quadrilateral plate and disrupting the obturator foramen.

Hip Dislocations

Posterior dislocation of the hip (Fig. 4-30) is the result of an abrupt deceleration injury such as occurs in motor vehicle accidents when the knee strikes the dashboard. It is commonly associated with fractures of the posterior rim or wall of the acetabulum. In adolescents, this injury may cause separation of the capital femoral epiphysis. On frontal radiographs, the femoral head is dislocated from the acetabulum and lies in a superolateral position. The involved femoral head appears smaller than the contralateral one because it is located closer to the radiographic plate (or film), and there is internal rotation of the femur. The injury is obvious on a true lateral projection. Osteonecrosis of the femoral head and secondary osteoarthritis of the hip joint are known complications.

Figure 4-30 Dislocations of the hip. A, Anteroposterior radiograph of the pelvis demonstrates a superolaterally dislocated right femoral head relative to the acetabulum (arrow). This is a classic appearance of a posterior dislocation, in contrast to anterior dislocations in which the femoral head lies anteromedial to the acetabulum. B, Coronal reformatted CT image at the level of the posterior acetabulum reveals a comminuted fracture of the posterior wall (arrow), an injury commonly associated with posterior hip dislocation.

Anterior dislocation of the hip accounts for 10% to 15% of all hip dislocations. It is caused by forced abduction and external rotation of the hip. The femoral head is displaced either anteromedially toward the superior pubic ramus or toward the obturator foramen. Usually, it is a simple dislocation without associated injury. An impacted fracture of the femoral head due to compression of the head on the dense acetabular rim (Hill-Sachs type of fracture) may occur. On frontal radiographs, there is medial displacement of the femoral head with respect to the acetabulum. A lateral view of the hip is diagnostic.

Central hip dislocation (protrusio) is nearly always associated with acetabular fractures. The femoral head protrudes into the pelvic cavity through the fractures of the acetabulum.

Fractures of the Proximal Femur

Fractures of the proximal femur are classified on the basis of their anatomic location into femoral head, neck, trochanteric, intertrochanteric, and subtrochanteric. These fractures can also be categorized by their relationship to the joint capsule into two groups: intracapsular or extracapsular. Fractures of the femoral head and neck (subcapital and transcervical types) are considered intracapsular. Trochanteric, intertrochanteric, and subtrochanteric fractures are extracapsular. Basicervical femoral neck fractures are generally acknowledged as extracapsular fractures. The distinction between the two is important for determination of treatment and prediction of outcome. Intracapsular fractures have a significantly increased incidence of avascular necrosis. Extracapsular fractures usually heal well but are more prone to be unstable. In elderly patients, proximal femoral fractures can be very subtle and may occur in the setting of minor trauma owing to underlying osteoporosis. MRI should be strongly considered for evaluation of the hip in this context, even after negative plain radiographs. Fractures of the femoral head occur with dislocations and appear as impaction or shear injury.

Fractures of the Femoral Neck

Femoral neck fractures are common in the elderly population, particularly women, due to the high prevalence of osteoporosis, which is strongly associated with this type of fracture. They are divided into subcapital, transcervical, and basicervical types. The more proximal and displaced, the higher is the incidence of avascular necrosis and nonunion.

Subcapital fracture (Fig. 4-31A and B) is the most common type and may be extremely subtle. There is a disruption and angulation at the junction of the superior cortex of the femoral neck with the femoral head. The Garden classification categorizes subcapital fractures into four stages based on the position of the principal (medial) compressive trabeculae of the femoral head and neck and the acetabular trabeculae on frontal radiographs. Stage I fractures are incomplete fractures that spare the inferior femoral neck trabeculae. There is abduction of the superior portion of the femoral neck due to external rotation of the femoral shaft and valgus of the femoral head. The principal compressive trabeculae of the head and neck are aligned in a mild valgus position. Stage II fractures are complete fractures without displacement. The principal compressive trabeculae of the femoral head and neck are aligned in mild varus or near anatomic position. Stage I and stage II fractures are generally stable and have a good prognosis. However, when this fracture is subtle and impacted in near anatomic position, it may permit ambulation and be relatively painless. Stage III fractures are complete fractures with partial displacement. There is more severe varus alignment of the trabeculae of the femoral head and neck. In addition, the trabeculae of the femoral head are not aligned with the acetabular trabeculae. Stage IV fractures are complete fractures with full displacement. The femoral shaft is not only externally rotated but also telescoped, and the femoral head remains in anatomic alignment with the acetabulum; therefore the trabeculae of the femoral head and the acetabulum are parallel.

Figure 4-31 Fractures of the proximal femur. A and B, Subcapital femoral neck fracture. Anteroposterior radiograph of the left hip (A) demonstrates a subcapital femoral neck fracture. The fracture line itself is visualized as a band of apparent sclerosis (black arrows). Coronal T1-weighted MR image (B) confirms the presence of a fracture line (arrow) in the femoral neck. C, Isolated fracture of the greater trochanter. Anteroposterior radiograph of the left hip demonstrates a fracture of the greater trochanter (white arrows). D, Isolated pathologic fracture of the lesser trochanter due to plasmocytoma. Anteroposterior radiograph of the left hip reveals an avulsion fracture of the lesser trochanter (curved arrow) in an adult patient with multiple myeloma. E, Intertrochanteric fracture. T1-weighted MR image reveals an intertrochanteric fracture line (white arrowheads) in a patient in whom the plain radiographs (not shown) were interpreted as normal.

Transcervical and basicervical fractures are rare. Transcervical fractures are usually visible on frontal projections and have a varus deformity at the fracture site. Basicervical fractures are located at the base of the femoral neck, just proximal to the intertrochanteric crest. They have a higher incidence of avascular necrosis than the more distal intertrochanteric fractures.

Trochanteric Fractures

Isolated fractures of the greater trochanter (Fig. 4-31C) are common in osteoporotic women with a history of fall on their lateral side. The normal irregularity in this region makes it difficult to detect this type of fracture, especially when it is not displaced.

Isolated fractures of the lesser trochanter in children or adolescents are usually due to avulsion injuries of the apophysis from a forceful pull by the iliopsoas muscle tendon, which inserts on the lesser trochanter. In adults, an isolated lesser trochanter fracture (Fig. 4-31D) is unusual and should raise the suspicion of underlying pathology, especially metastatic disease.

Intertrochanteric Fractures

Intertrochanteric fractures (Fig. 4-31E) are the most common type of extracapsular fracture of the proximal femur. These fractures occur in an older population than do femoral neck fractures; men and women are equally affected. They are classified according to the number of separate fragments into two-, three-, or four-part, depending on the involvement of the lesser or greater trochanter. The main fracture line is usually an oblique line extending along the plane that joins the greater and lesser trochanters. Type 0 fractures are nondisplaced and most subtle. Type I fractures are two-part fractures. Type II fractures are three-part fractures consisting of a proximal fragment, a distal fragment, and either trochanter. Type III fractures are four-part fractures consisting of a proximal fragment, a distal fragment, and both trochanters. The status of the lesser trochanter is a very important component of intertrochanteric fractures because, if fractured, it typically includes a large fragment of cortex of the femoral neck. Comminution of the posteromedial cortex, subtrochanteric extension, or a reverse obliquity pattern (when the main fracture line runs perpendicular to the line joining the greater and lesser trochanters) makes the fracture unstable.

Subtrochanteric Fractures

The subtrochanteric region encompasses the area below the lesser trochanter to 5 cm distally in the shaft of the femur. Fractures in this region are distinguished from intertrochanteric fractures by the location of the fracture line in the proximal femoral shaft. They are frequently comminuted with marked displacement owing to the various muscle attachments.

Fractures of the Femoral Shaft

Femoral shaft fractures are the most common long bone fractures in patients with multiple injuries. A violent, severe, high-energy trauma is required to cause these fractures because the femur is the strongest and the heaviest bone in the body. Radiographic evaluation must include the regions of the hip and tibia to assess for potential associated injuries such as proximal femoral fractures, acetabular fractures, and tibial fractures.

Hemarthrosis/Lipohemarthrosis

The appearance of knee hemarthrosis is similar to other types of joint effusion in that there is an oval-shaped density obliterating the lucent space anterior to the femoral cortex on the lateral radiograph (suprapatellar recess). If the effusion is large, it will cause anterior displacement of the quadriceps femoris muscle, suprapatellar tendon, and patella.

On the other hand, the presence of blood mixed with liquid fat in the knee joint, or lipohemarthrosis (Fig. 4-32), suggests the presence of an intra-articular fracture of the distal femur or proximal tibia. The fracture permits the flow of blood and liquid fat from the medullary cavity into the joint space. The sign is visualized in a horizontal-beam (cross-table) lateral radiograph taken with the patient in the supine position. The joint capsule is distended with a layering fat–blood interface that resembles an air–fluid level, called the “fat–blood interface” (FBI) sign. The presence of lipohemarthrosis is very useful as it aids in the identification of a minimally displaced intra-articular fracture. Pneumolipohemarthrosis and pneumohemarthrosis have a very similar radiologic characteristic, except that air has greater lucency than fat. It signifies an open, intra-articular fracture of the distal femur or proximal tibia.

Figure 4-32 Lipohemarthrosis and pneumohemarthrosis. A and B, Lipohemarthrosis. Lateral cross-table radiograph of the knee shows a fat fluid level (arrowheads) in the suprapatellar bursa. Sagittal reformatted CT image of the same patient depicts the same finding. The fat blood interface (FBI) sign of lipohemarthrosis is shown.

Fractures of the Distal Femur

Fractures of the distal femur are caused by a severe axial load with varus, valgus, or rotational force. In younger individuals, these are usually a result of motor vehicle accidents. In elderly populations, a minor slip and fall on a flexed knee can result in these types of fractures. The supracondylar area of the femur is defined as the zone between the femoral condyles and the junction of the distal metaphysis and diaphysis of the femur. There are three types of supracondylar fractures, classified by the AO/OTA: extra-articular supracondylar, intra-articular unicondylar, and intra-articular bicondylar. Extension to the knee joint is frequently the result of a vertical intercondylar component. “Floating knee” (Fig. 4-33) is a term used when these fractures are associated with tibial shaft fractures, creating a free, large, segmental fragment that includes the knee joint. The incidence of arterial injury is low at 2% in supracondylar fractures.

Figure 4-33 Floating knee. A and B, Frontal radiographs of the femur, tibia, and fibula of the right (R) leg reveal a segmental fracture of the midshaft of the femur, and midshaft fractures of both bones of the leg. This combination of fractures results in a free, large segmental fragment consisting of the knee joint. C, Volumetric (3D) CT reformation beautifully displays the long bone fracture sites (white arrows).

Knee Dislocations

Knee dislocation is a rare injury. It is classified according to the relationship of the tibia with the femur into anterior, posterior, medial, lateral, and rotational dislocations. Anterior dislocation (Fig. 4-34A and B) is the most common type, resulting from severe hyperextension. The incidence of vascular injuries in knee dislocations varies from 7% to 64% in different series. Clinical evidence of vascular injuries should be sought in every knee dislocation. Knee dislocations are commonly associated with avulsion fractures of the tibial articular surface and with tears of the cruciate ligaments, joint capsule, and extracapsular ligaments. Injuries to these stabilizing structures are best evaluated with MR.

Figure 4-34 Dislocations around the knee. A and B, Frontal and lateral radiographs of the knee demonstrate an anteriorly dislocated tibia relative to the femur. This is a classic anterior knee dislocation with a complete bicruciate ligament tear subsequently confirmed with MRI (not shown). Anterior knee dislocation is frequently associated with traction injury of the popliteal artery. C and D, Lateral patellar dislocation is depicted on frontal (curved arrow) and lateral radiographs of the knee.

Patellar Dislocations

The patella is normally located in the sulcus of the anterior distal femur. Dislocations of the patella (Fig. 4-34C and D) are caused by excessive internal rotation of the femur on a fixed foot, and are usually relocated prior to clinical presentation. These dislocations are invariably lateral, with disruption of the medial retinaculum. The preferential lateral dislocation occurs because the lateral femoral condyle arc is shallower than the medial condyle. Patellar dislocations may be associated with chondral or osteochondral fractures, which typically arise from the lateral margin of the lateral femoral condyle or from the articular surface of the medial patellar facet. Presence of fragments in the joint space may impair joint motion and lead to locking or degenerative changes of the knee. The classic MR imaging findings of recent patellar dislocation include hemarthrosis, disruption of the medial patellar retinaculum, lateral patellar tilt, and bone contusions in the lateral femoral condyle and medial patellar facet.

Fractures of the Patella

The majority of fractures of the patella are caused by a direct blow from a fall or motor vehicle accident. Approximately 60% of patellar fractures involve the mid-body and are transverse (Fig. 4-35A and B), 25% are stellate or comminuted, and 15% are vertical (Fig. 4-35C). Displacement is present when there is separation of the fragments of more than 3 mm, or articular incongruity of 2 mm or greater. Displaced fractures may occur at the proximal or distal pole. The former may cause a low-lying patella due to the unopposed pull from the patellar tendon inferiorly (patella baja) (Fig. 4-35D). Alternatively, patella baja is seen in patients with quadriceps tendon tear. A high-riding patella (patella alta) (Fig. 4-35E and F) may be seen in distal pole fractures or in patients with patellar tendon tears.

Figure 4-35 Fractures of the patella. A and B, Frontal and lateral radiographs of the knee demonstrate a comminuted fracture of the patella with the main transverse fracture line (arrow) traversing through its mid-body. There is separation of the proximal and distal fragments due to traction from the quadriceps superiorly and patellar tendon inferiorly. C, Vertical nondisplaced fracture (arrow) of the patella is barely seen on the frontal radiograph. This emphasizes the need for obtaining routine four views of the knee in patients with acute knee injury. D, Lateral radiograph of the knee shows an avulsion fracture of the proximal pole of the patella (arrowhead), which causes low-lying patella due to unopposed pull from the patellar tendon (patella baja). E and F, High-riding patella (patella alta) is due to unopposed action of the quadriceps in this patient with distal pole fracture of the patella (arrowhead). Sagittal MR image (F) confirms a complete disruption with retraction of the patellar tendon (arrowhead).

Fractures of the Tibial Plateau

Fractures of the tibial plateau are severe injuries caused by high-speed motor vehicle accidents or falls from high altitudes. Axial loading, valgus stress, or both is the usual mechanism. The fractures may involve the medial plateau, the lateral plateau, or both, with extension into the metadiaphysis of the tibia. Fractures of the lateral plateau are the most common type because of the stronger cancellous trabeculae of the medial plateau. As a result, an isolated medial plateau fracture is the least frequent type. Schatzker’s widely used classification system categorizes tibial plateau fractures into six types according to fracture appearance, location, and extension. Type I is a split fracture of the lateral plateau. The fracture line causes a wedge-shaped fracture fragment. Type II (Fig. 4-36A and B) is a split-depression fracture of the lateral plateau. In addition to a cleavage fracture of the lateral plateau, the articular surface is depressed into the metaphysis. Type III (Fig. 4-36C) is a pure depression fracture of the lateral plateau with an intact osseous rim. Type IV is a medial plateau fracture, subdivided into IVA (split) and IVB (depressed) subtypes. In type V, the fracture line has the configuration of an inverted “Y.” The metaphysis and diaphysis remain intact. Type VI (Fig. 4-36D and E) is a tibial plateau fracture with dissociation between the tibial metaphysis and diaphysis. These fractures may involve either one or both plateaus, and have varying degrees of comminution. The goal of imaging is to demonstrate the number of fracture fragments, degree of displacement, degree of depression, location, and type of plateau fractures. Meniscal injuries, especially of the lateral meniscus, are seen in up to 50% of cases of tibial plateau fractures. Injuries to the medial collateral ligament and anterior cruciate ligament are also common.

Figure 4-36 Fractures of the tibial plateau. A and B, Volumetric (3D) CT images demonstrate a fracture of the lateral tibial plateau that has two components of a split (arrows) and depression (arrowheads) (type II) fracture. CT accurately depicts the fragments, degree of depression, amount of joint space involved, and displacement. C, Oblique radiograph of the knee shows a pure depression fracture of the lateral tibial plateau (arrowheads) (type III). D and E, Oblique radiograph of the knee and volumetric (3D) CT image demonstrate a comminuted fracture of both medial and lateral tibial plateaus (arrowhead) with dissociation between the tibial metaphysis and diaphysis (arrows). An avulsion fracture of the tibial spine is noted (short arrows) on the CT reformation (E).

Avulsions About the Knee

Avulsion of the Anterior Cruciate Ligament Insertion

The distal attachment of the anterior cruciate ligament (ACL) is at the medial spine of the intercondylar eminence of the tibia. Avulsions of the medial tibial spine usually occur in children or adolescents. Radiographic findings include a fracture at the base of the intercondylar eminence, or of the medial tibial spine (Fig. 4-37A), which indicates that the ACL has been detached. It should be noted that isolated fractures of the lateral tibial spine do not involve either cruciate ligament. In some cases, the presence of avulsed bony fragments in the joint may have an appearance similar to a loose body or an osteochondral fracture.

Figure 4-37 Avulsions about the knee. A, Anterior cruciate ligament (ACL) avulsion. Coronal reformatted CT image of the knee shows an avulsion fracture of the medial tibial spine (arrow), the attachment site of the ACL. In addition, there is a nondisplaced split fracture (arrowheads) of the medial tibial plateau. B and C, Posterior cruciate ligament (PCL) avulsion. Lateral cross-table radiograph (B) of the knee demonstrates a lipohemarthrosis (arrowheads). A subtle bone fragment (arrow) is visualized at the tibial attachment of the PCL. Sagittal fat-suppressed T2-weighted MR image (C) confirms the fracture site (arrow) at the distal attachment of the PCL (arrowheads). D, Segond fracture. An avulsion fracture (arrow) of the lateral tibial plateau is shown in a frontal radiograph of the knee. ACL and meniscal injuries are commonly associated with Segond fracture.

Fractures of the Ankle

Ankle fractures (Box 4-17) are most commonly classified by their appearance on radiographs. Certain radiographic features can be used to determine the mechanism and to understand these complex injuries. Two major mechanisms responsible for ankle fractures are rotational and axial-loading injuries. Rotational malleolar fractures are less severe injuries than axial-loading tibial plafond or pilon fractures.

Rotational malleolar fractures are caused by combinations of different forces: supination, pronation, external rotation, adduction, and abduction. These forces result in either impaction injury or avulsion injury to the malleoli. The characteristic of impaction injury is an oblique fracture line, while the characteristic of an avulsion injury is a horizontal fracture line. These fractures are typically described by the location of malleolar fracture lines (medial, lateral, or posterior malleoli, or more). Bimalleolar or trimalleolar fractures are injuries that involve more than one structure. The detailed description should include the level of the fibular fracture, orientation of the fracture line (horizontal or oblique), possibility of syndesmosis disruption, involvement of the tibial plafond, and size of the various fragments. Several classifications are used in the assessment of ankle fractures. The Weber/AO classification is simple and correlates well with treatment and prognosis. The level of the fibular fracture determines the extent of injury to the syndesmotic complex, and is used to categorize fractures in this classification. In general, the higher the fibular fracture, the more extensive the damage to the syndesmosis and the greater the risk of ankle instability. Type A (Fig. 4-38A) is a supination-adduction injury with the fibular fracture located below the syndesmosis. There is a transverse fracture of the lateral malleolus or lateral collateral ligament rupture and an oblique fracture of the medial malleolus. Type B (Fig. 4-38B) is a supination-external rotation or pronation-abduction injury resulting in a fracture of the fibula at the level of the syndesmosis. There is an oblique fracture of the lateral malleolus and a horizontal fracture of the medial malleolus or deltoid ligament rupture. There is partial disruption of the syndesmosis. Type C is a pronation-external rotation injury with a fracture of the fibula above the level of the syndesmosis. There is a transverse fracture of the medial malleolus or deltoid rupture, and rupture of the syndesmosis. Type C (Fig. 4-38C) is usually treated with syndesmotic fixation in addition to stabilization of the lateral malleolus. Maisonneuve’s fracture (Fig. 4-38D and E) is part of the spectrum of pronation-external rotation injuries, in which the fibular fracture is more proximal and there is a tear of the full length of the interosseous membrane. Fractures of the proximal fibula are easily overlooked because of the distracting painful injuries at the ankle. The diagnosis of Maisonneuve’s fracture should be considered in the following situations: isolated fracture of the posterior lip of the tibia, isolated displaced fracture of the medial malleolus, and widening of the medial or lateral clear spaces without evident fracture of the lateral malleolus or fibula. In these circumstances, full-length views of the tibia and fibula should be obtained to identify associated fractures of the proximal fibula.

Figure 4-38 Fractures of the ankle. Three types of rotational malleolar fracture. A, Type A. The fibular fracture line (arrows) is located completely below the level of the syndesmosis. B, Type B. The fibular fracture (arrows) begins at the level of the syndesmosis. There is widening of the medial mortise (arrowheads) indicating a deltoid ligament injury. C, Type C. Fibular fracture (arrows) is above the level of syndesmosis. There is disruption of the syndesmosis (widening of the tibiofibular space, white arrowheads) up to the level of the fibular fracture as well as a deltoid ligament injury with a widened mortise (black arrowheads). D and E, Maisonneuve’s fracture. Frontal radiograph of the ankle shows an isolated posterior malleolar fracture (arrows) that prompted a request for an additional radiograph to include the whole length of the fibula. An oblique fracture (arrow) of the proximal fibula is revealed. F, Tibial plafond (pilon) fracture. Anteroposterior radiograph of the ankle demonstrates a severely comminuted intra-articular fracture of the distal tibia extending to the tibial plafond. The malleoli are in anatomical alignment.

Axial loading to the ankle joint drives the talus against the distal tibial articular surface, resulting in tibial plafond fractures (Fig. 4-38F). The malleoli usually maintain an anatomic relationship with the talus. These fractures are more severe than the rotational malleolar fractures. They are comminuted, intra-articular fractures of the distal tibia. Differentiation of these fractures from trimalleolar fractures lies in the profound comminution of the distal tibia, intra-articular extension to involve the dome of the plafond, common association with talar fractures, and preservation of the tibiofibular syndesmosis. Post-traumatic arthritis is a common complication of displaced plafond fractures. Tillaux fracture is an avulsion of the anteroinferior tibiofibular ligament from the lateral distal tibial margin, created by forceful external rotation of the foot. The vertical fracture line extends from the distal articular surface of the tibia superiorly to the lateral tibial cortex. If there is lateral displacement of more than 2 mm, or step-off of the articular surface of the distal tibia, surgical fixation is usually required. In children, this fracture is a Salter Harris type III, since the medial side of the growth plate fuses earlier than the lateral side. In adults, this is usually a ligamentous injury. An avulsion fracture of the medial margin of the fibula at the attachment of the anterior tibiofibular ligament is known as the Wagstaffe-LeFort fracture. Isolated Tillaux fractures and Wagstaffe-LeFort fractures do occur, but are more commonly part of more extensive injuries to the ankle mortise and are associated with malleolar fractures.

Triplane fractures (Fig. 4-39A–C) are distinct fractures of the distal tibial epiphysis, caused by plantar flexion and external rotation. There are fracture lines in three planes: a horizontal plane within the growth plate or physis, a sagittal plane through the epiphysis, and an oblique vertical plane in the posterior distal metaphysis. There are two distinct types of triplane fractures: two-fragment and three-fragment fractures. The appearance of the two-fragment fractures is very similar to that of Tillaux fractures, except that there is a metaphyseal component on the lateral view. In the three-fragment fracture, the entire epiphysis is usually displaced posteriorly, whereas in a two-fragment fracture only a portion of the epiphysis is displaced. It is important to distinguish between the two because three-fragment fractures usually require open reduction and internal fixation to preserve the joint.

Figure 4-39 Fractures of the ankle. A, Tillaux fracture. Mortise view of the ankle shows a vertical fracture of the distal articular surface of the tibia extending to the lateral tibial cortex (arrow, Salter Harris type III in this case). B and C, Triplane fracture. Coronal reformatted CT image (B) demonstrates the typical findings of a Tillaux fracture (arrows). On the sagittal reformation (C) there is a coronally oriented vertical metaphyseal component of the fracture (arrowhead), thereby completing the three components of a triplane fracture. Note also a nondisplaced fracture of the calcaneus. Triplane fracture is a combination of a fracture line extending in three planes (sagittal epiphysis, axial physis, and coronal metaphysis). Note a nondisplaced fracture of the calcaneus (curved arrow).

Injuries to the Hindfoot

Subtalar or peritalar dislocation is a rare injury characterized by concomitant dislocations of the subtalar and talonavicular joints with normal tibiotalar relationship. Findings are obvious on lateral radiographs, with absence of the talar head in the cup of the navicular. Medial subtalar dislocation (Fig. 4-40A and B) is far more common than lateral subtalar dislocation, while the latter is more severe. Total talar dislocation is a combined complete dislocation of both the tibiotalar (ankle) and subtalar joints. It is the most serious of all talar injuries.

Figure 4-40 Fractures and dislocation of the hindfoot. A and B, Subtalar dislocation. Frontal and lateral radiographs of the ankle demonstrate a medial subtalar dislocation. On the lateral projection, the empty navicular cup is obvious (arrowheads). C, A fracture of the talar neck (arrows) is seen on a lateral radiograph. D, Lateral radiograph shows a comminuted fracture of the calcaneus extending vertically (black arrowheads) through the body, posterior to the subtalar joint, and longitudinally toward the posterior facet (white arrowheads). Subtalar joint extension is suspected (star). Bohler’s angle (formed by the black and white lines) is decreased to less than 20 degrees (white arrow). E, Coronal reformatted CT image at the widest point of the lateral process of the talus helps classify the type of fracture. This fracture has a single subtalar joint extension (arrow), therefore producing two articular pieces.

Fractures of the Talus

Talar fractures are the second most common site of tarsal fracture and are usually caused by forced dorsiflexion. Fractures are classified by anatomic location: head, neck, body, posterior process, and lateral process. Fractures of the talar head are rare; they usually involve the talonavicular joint and are associated with talonavicular subluxation. The talar neck is the most vulnerable site. Fractures of the talar neck (Fig. 4-40C) are defined when the fracture line is anterior to the lateral process of the talus. They are usually oriented in a vertical plane and not displaced. Hawkins’s classification divides these fractures into four types. Type I is a nondisplaced fracture. Type II is a fracture with subtalar subluxation or dislocation. Type III is a fracture with subtalar and tibiotalar dislocation. Type IV is a fracture with subtalar subluxation and dislocation of the talonavicular joint. The risk of avascular necrosis is 15%, 40% to 50%, and 100%, respectively, for types I, II, and III/IV. Aviator’s astragalus is an eponym for a displaced fracture of the talar neck that results in medial displacement and rotation of the distal fragment together with the bones of the foot. Fractures extending into, or posterior to, the lateral process of the talus are defined as fractures of the talar body. These are intra-articular fractures and have a high rate of avascular necrosis. Fractures of the posterior process of the talus are uncommon and best seen on the lateral view. An os trigonum is the main differential diagnosis, although this usually has a well-corticated edge and smooth surface. Isolated fractures of the lateral process are frequently overlooked and misinterpreted as a severe sprain. This is usually an avulsion fracture and best visualized on the mortise view.

Fractures of the Calcaneus

The calcaneus is the most common site of tarsal bone fracture. Fractures are classified by their location and the presence of subtalar joint involvement. Calcaneal fractures with subtalar joint involvement (Fig. 4-40D and E) are more common (75% of all calcaneal fractures). They result from axial-loading forces to the body of the calcaneus through the talus. Typically, there is loss of height, increased width, and disruption of the subtalar joint facet. Boehler’s angle is generally decreased. The axial-loading force produces two separate fracture lines: shear and compression lines. The shear fracture line is a sagittal plane fracture through the posterior facet, dividing it into sustentacular and tuberosity fragments. The tuberosity fragment is usually impacted, rotated, and displaced laterally, resulting in loss of calcaneal height and increased calcaneal width. The compression fracture line is a coronal plane fracture that splits the middle facet. When viewed from the lateral side, this line has the shape of an inverted Y. The Sander classification relies on the number of articular pieces of the posterior facet of the subtalar joint; prognosis worsens as the number of fragments increases. Occasionally, there is ligament entrapment between the fragments, or involvement of the sinus tarsi. Calcaneal fractures are frequently bilateral, and 10% are associated with fractures of the thoracolumbar spine.

The rest of the fractures, which do not involve the posterior facet, are in this category. This includes fractures of the anterior process, mid-calcaneus (body, sustentaculum tali, peroneal tubercle, lateral calcaneal process), and posterior calcaneus (tuberosity, medial calcaneal tubercle). They account for 25% of all calcaneal fractures. Fractures of the mid-calcaneus are usually the results of axial-loading mechanisms, while avulsion forces or inversion injuries cause the others.

Injuries to the Midfoot

The midfoot is defined as the region distal to Chopart’s joint and proximal to Lisfranc’s joint. The navicular, cuboid, and medial, middle, and lateral cuneiforms make up the bones of the midfoot. The midfoot is responsible for maintaining the relationship between the forefoot and the hindfoot. Navicular fractures are commonly due to an indirect force that occurs in sports-related injuries, falls, or motor vehicle accidents. Less likely, they may be the result of a direct blow that causes an avulsion of the talonavicular or naviculocuneiform ligaments. These fractures are categorized by their location: tuberosity (medial prominence of the navicular) and body. An accessory navicular (os tibiale externum) bone can be mistaken for a fracture of the tuberosity. This accessory ossicle is present in up to 25% of the population, and is bilateral 90% of the time. Cuboid and cuneiform injuries are commonly seen with other injuries to the midfoot and Lisfranc’s joint.

Tarsometatarsal (Lisfranc) Injuries

Injuries to the tarsometatarsal joint range from a stable sprain to a grossly unstable deformity. These injuries can result in a prolonged recovery period and significant long-term disability, and it is therefore important to recognize and treat them early. Up to 20% are missed on initial presentation. They are commonly the result of indirect forces that cause plantar hyperflexion across the long axis of the foot. This can occur with minimal trauma (e.g., foot entrapment on the car brake pedal, or a minor fall), and as a sports-related injury (e.g., opponent falling on the foot in fixed equinus). A key anatomic structure related to this type of injury is Lisfranc’s ligament. This is the strongest and largest ligament of this joint complex, originating from the lateral plantar aspect of the medial cuneiform and inserting on the medial plantar aspect of the second metatarsal base. It is an indirect link between the first and second metatarsals, and the only ligamentous support between the medial portion of the forefoot and the rest. The nidus of Lisfranc’s injuries is typically at the medial cuneiform and the base of the second metatarsal, where Lisfranc’s ligament is located. This ligament may be torn, without fractures of the medial cuneiform or base of the second metatarsal, or may be intact with a fracture of the base of the second metatarsal. Two major types of these injuries are described. The homolateral type (Fig. 4-41) is a lateral dislocation of the four lateral metatarsals or all metatarsals. The divergent type is a less common, but more severe injury. In this type, there is lateral displacement of the second through fifth metatarsals with medial displacement of the first metatarsal. Rarely, an isolated medial dislocation of the first metatarsal and medial cuneiform may occur. The most common fractures associated with these dislocations are fractures of the base of the second metatarsal. Chip fractures of the distal margin of the cuboid, and base of other metatarsals, are frequent.

Figure 4-41 Lisfranc’s injury. Anteroposterior radiograph of the foot demonstrates homolateral lateral dislocation of the tarsometatarsal joints. Lisfranc’s ligament is completely torn, as indicated by the complete lateral dislocation of the second metatarsal with respect to the medial and middle cuneiforms.

Metatarsal Fractures

The majority of injuries to the fifth metatarsal are related to sporting or athletic activities. These fractures are separated into two groups: proximal base fractures and distal spiral or dancer’s fractures. There are three distinct fracture patterns of the proximal fifth metatarsal as defined by the location of the fracture line. Zone 1 injury (Fig. 4-42A) is an avulsion fracture at the base of the fifth metatarsal that usually occurs from an indirect load. Tension is produced along the insertion of the lateral band of the plantar aponeuroses during sudden inversion of the hindfoot, causing disruption of the bony cortex. Zone 2 injuries (Fig. 4-42B) are true Jones fractures and involve the metadiaphyseal junction of this bone. The fracture line propagates from the lateral aspect of the proximal metatarsal toward the articular surface between the fourth and fifth metatarsal bones and may progress into the metatarsocuboid joint. It is the result of tensile stress along the lateral border of the metatarsal. Zone 3 injuries are located in the proximal fifth metatarsal. Relative frequency of these fractures is 93% zone 1, 4% zone 2, and 3% zone 3. An apophysis of the fifth metatarsal should not be mistaken for a fracture as it has an obliquely longitudinal orientation to the axis of the metatarsal. Dancer’s fracture is a spiral, oblique fracture of the distal fifth metatarsal caused by rolling over the outer border of the foot.

Figure 4-42 Fractures of the proximal fifth metatarsal bone. A, Zone 1 injury is an avulsion fracture at the base of the fifth metatarsal (arrow). This is the most common type of fracture of the proximal fifth metatarsal. B, Zone 2 injury, or “true Jones fracture,” involves the metadiaphyseal junction (arrow).

Metatarsophalangeal Injuries

Injuries to the metatarsophalangeal (MTP) joint complex can occur in isolation or as part of multiple trauma. Most commonly, they involve the first MTP joint, which normally provides stable load sharing between the metatarsal head and the toe. Dislocations of the first MTP joint can be complicated with avulsion injuries of the medial or lateral collateral ligaments, or displacement of the sesamoid structures. The sesamoids function within the first MTP joint complex as shock absorbers and fulcrums to support the weight-bearing function of the first toe. The spectrum of sesamoid injuries is wide, ranging from sesamoiditis to stress fracture and acute fracture. Acute fractures are caused by a direct blow, axial loading, or hyperpronation. Depending on the mechanism of injury, the fractures can be transverse, comminuted, or stellate. The medial sesamoid is more commonly injured than the lateral. A partite sesamoid can be distinguished from a fracture by its smooth, sclerotic edge.

Phalangeal fractures are the most common injury to the forefoot. Fractures occur most commonly in the proximal phalanges. Of these, the proximal phalanx of the fifth toe is involved most often. Two major mechanisms result in fractures: direct blow (e.g., heavy object dropped onto the foot) and axial loading (stubbing injury). The former usually causes a comminuted or transverse fracture. The latter tends to produce more deformity due to secondary valgus or varus forces, and results in spiral or oblique fractures.

Interphalangeal dislocations are a result of axial loading applied to the terminal end of the unprotected digit. Proximal interphalangeal joint dislocations are more common.