Mechanism and Patterns of Injury

Perilunate injuries are a spectrum of carpal injuries that are the result of high-energy trauma. The mechanism of injury is typically hyperextension, ulnar deviation, and intercarpal supination of the wrist. Indirect forces typically cause perilunate injuries when the point of rotation is distal to the radius and there is more stress on the carpal bones. In very young patients, such a force typically results in a physeal injury to the distal radius, and in older patients with osteopenic bone, a distal radius fracture typically occurs through the soft bone of the distal radius. This probably explains why perilunate injuries are typically seen in young patients with good bone quality who are involved in high-energy activities.

Mayfield^3,6,7 described a spectrum of progressive perilunar instability that has greatly enhanced understanding of these injuries. Perilunate injuries are divided into four stages based on the concept of a sequential pattern of traumatic intercarpal wrist instability.

All perilunate injuries except the very rare “reverse perilunate” begin with injuries on the radial side of the wrist and progress ulnarward. The first stage in lesser arc injuries is scapholunate dissociation followed by lunocapitate dislocation with lunotriquetral disruption and finally lunate dislocation from the radius. A lesser arc injury is a purely ligamentous injury that typically manifests with dorsal dislocation of the capitate from the lunate and rarely with lunate dislocation toward the carpal tunnel.

Mayfield also noted that carpal fractures may occur in perilunate injuries in lieu of ligament ruptures. In these cases, the force is concentrated on the carpus away from the lunate as it progresses from radial to ulnar, which results in the carpal bone fractures. The injuries that result are called greater arc injuries because the route of injury includes a path more remote from the lunate than lesser arc injuries (Fig. 43-1).

FIGURE 43-1 Greater and lesser arc injuries of the wrist. Lesser arc injuries result in a disruption of ligaments that bind the carpus to the lunate. The path of injury passes close to the body of the lunate and results in a purely ligamentous injury to the wrist. Greater arc injuries occur following a force that disrupts the carpus in a path further away from the lunate. Greater arc injuries may often include carpal bone fractures and avulsion fractures of the radial and ulnar styloids in a variety of combinations.

Progressive perilunar instability as described by Mayfield has four stages that follow a common sequence after exposure of the wrist to forceful hyperextension with a strong supination torque (Fig. 43-2). Stage I injuries result in scapholunate dissociation.^6,7 Hyperextension of the scaphoid places a strong torque on the lunate and its ligaments. The extrinsic palmar and dorsal ligaments tightly stabilize the lunate, and the force is concentrated on the scapholunate ligament, which ultimately begins to tear from palmar to dorsal. If the force is strong enough, the scapholunate ligament completely ruptures, completing stage I.

FIGURE 43-2 The four stages of perilunar carpal instability. Stage I: As the distal carpal row is forced into extension (arrows), the scaphotrapeziocapitate ligaments (1) pull the scaphoid into extension, opening the space of Poirier (asterisk). The lunate is constrained by the short radiolunate ligament (2), and the hyperextension force of the scaphoid results in concentration of energy to the scapholunate ligament. A scapholunate ligament rupture or scaphoid fracture may occur. The scapholunate ligament usually ruptures from palmar to dorsal with complete dissociation noted when the dorsal portion of the scapholunate ligament fails (3). Stage II: Midcarpal dislocation may occur with the capitate usually moving dorsal to the lunate. The midcarpal translation is limited by the integrity of the radioscaphocapitate ligament (4). Stage III: If hyperextension and intercarpal supination progresses, the ulnar carpal ligaments (5) and the lunotriquetral interosseous ligament (6) may fail. Stage IV: In end-stage injury, additional hyperextension forces the capitate to push the lunate palmarly through the torn volar capsule and the space of Poirier. The lunate may dislocate into the carpal tunnel hinged on the intact short radiolunate ligament (2).

In stage II injuries, there is sufficient force to dislocate the midcarpal joint with the capitate typically dislocating dorsal to the lunate. Midcarpal dislocation requires additional injury to the extrinsic ligaments, including the scaphocapitate and radioscaphocapitate. The space of Poirier, which is a deficiency in the palmar wrist capsule between radial and ulnar capsular ligaments, is opened by the progressive injury with a palmar capsular rent that exposes the midpalmar joint. In stage III injuries, the force continues in an ulnar direction with rupture of the lunotriquetral ligament and may include additional capsular injuries to the ulnolunate ligaments.

In stage IV injuries, the lunate is forced volarly to dislocate into the carpal tunnel through the opened space of Poirier. Isolated volar dislocations of the lunate are the end stage of the spectrum of progressive perilunar instability. Lunate dislocations are divided into three types. Type 1 lunate dislocations result in a lunate that has rotated palmarly up to 90 degrees. Type 2 lunate dislocations produce a lunate with more than 90 degrees of palmar rotation as it is hinged on the short radiolunate ligament. Type 3 injuries result in dislocation of the lunate into the carpal tunnel. Reverse perilunar instabilities result from hyperpronation of the wrist and may be the mechanism for rare perilunate injuries with palmar dislocation of the midcarpal joint.³

In greater arc injuries, the variable pattern of fracture might include avulsion of the radial styloid or fracture of the scaphoid, capitate, triquetrum, or ulnar styloid. The most common pattern observed in greater arc injuries is the trans-scaphoid perilunate fracture-dislocation. The trans-scaphoid variant is observed in 60% of perilunate wrist injuries.^1,3,6 The scaphoid fracture is through the waist in 60% to 72% of cases.^1,3 The scaphoid may fracture at any level, however, including the proximal pole.

Fracture of the capitate may occur and be part of the “scaphocapitate” syndrome.^3,6,8–10 This injury consists of a variation of a greater arc perilunate fracture-dislocation, in which the scaphoid and the capitate are fractured. The capitate fracture typically occurs proximally at the proximal neck of the bone. Complete rotation of the capitate fragment is typical with the proximal fragment often rotated 90 to 180 degrees. The mechanism of the fracture seems to involve a direct impact of the capitate against the dorsal lip of the radius with the wrist in a hyperextended and ulnarly deviated position. Rotation of the proximal capitate fragment is a result of the return of the distal fragment to its neutral position after dislocation (Fig. 43-3).

FIGURE 43-3 Scaphocapitate syndrome. Capitate fractures may occur with fracture of the scaphoid in greater arc perilunate injuries. The capitate fracture is usually through the neck and may occur after extreme wrist extension (I). The final wrist position after injury may result in the capitate rotated up to 180 degrees with the articular surface facing cancellous bone (II and III).

Greater and lesser arc injuries usually manifest with ligament ruptures on the ulnar side of the lunate, including complete rupture of the lunotriquetral ligament. Greater arc perilunate injuries may manifest with fractures of the triquetrum. Triquetral fractures may occur in any plane, but the most common pattern is a sagittal split in the body of the triquetrum or an avulsion fracture of the proximal pole.

Fractures of the radial or ulnar styloids also may be observed in greater arc perilunate injuries. These are typically smaller avulsion fractures, but may be of significant size and include the origins of major wrist stabilizers, such as the triangular fibrocartilage complex or radioscaphocapitate ligaments.

Presentation and Diagnosis

Patients who present with a perilunate fracture-dislocation have obvious pain and swelling of the hand and wrist. A full musculoskeletal examination and screening for concomitant axial or appendicular skeleton injuries is important because these represent high-energy injuries, and the patient may have sustained additional trauma.

Patients may present with symptoms of median or ulnar nerve compression. The incidence of acute carpal tunnel syndrome manifesting with perilunate injury ranges from 16% to 46%.¹¹ Most patients have resolution of nerve compression after closed reduction, but persistent nerve dysfunction after closed reduction may require urgent surgical decompression. Close attention should be paid to the patients’ neurovascular status, and the status of the median nerve in particular should be carefully established before and after reduction.

A standard four-view wrist series should be diagnostic of perilunate injuries and exhibit typical features. Most importantly, the dislocation of the midcarpal joint is best appreciated on the lateral view where lunocapitate dissociation can be easily visualized. The position of the lunate is best determined on the lateral view, which may reveal malrotation or dislocation of the lunate (Fig. 43-4).

FIGURE 43-4 A, The lateral injury film reveals dislocation of the midcarpal joint with dorsal dislocation of the capitate from the lunate. B, Midcarpal dislocation accompanied with palmar rotation of the lunate. C, Palmar dislocation of the lunate (Mayfield stage 4).

In perilunate injury, one also may appreciate on the anteroposterior view that there are radiographic breaks in the smooth arcs between the carpal rows described by Gilula.¹² These arcs are named after Gilula, the radiologist who described the concept of the greater and lesser arc injuries. Additionally, the carpus appears foreshortened with loss of carpal height. Malrotation of the lunate produces a “triangular-shaped” lunate that overlaps the capitate on the anteroposterior radiograph (Fig. 43-5). A cortical ring sign of the scaphoid consistent with rotary subluxation of the scaphoid also may be noted on the anteroposterior radiograph. Additionally, wrist films should be inspected for associated fractures of the radial styloid, scaphoid, capitate, hamate, triquetrum, and ulnar styloid, which may represent a greater arc injury.

FIGURE 43-5 Anteroposterior (AP) radiograph of the wrist may show additional signs of carpal injury. A, The lunate has a triangular appearance owing to pathological rotation. The scaphoid is flexed revealing the cortical ring sign consistent with rotary subluxation and carpal instability. B, Fractures of carpal bones or the radial or ulnar styloids are often best appreciated on the AP view and may signify a more significant injury, such as a perilunate wrist injury. C, Greater arc injury with markedly displaced scaphoid and capitate fractures. AP radiograph shows the degree of radial displacement in this case. The lunate remains reduced to the radius despite the severity of injury consistent with a perilunate mechanism of injury.

Sixteen percent to 25% of perilunate injuries are initially missed in the emergency department and manifest as chronic dislocations. Herzberg and colleagues¹ observed that the diagnosis was missed in 41 cases of 166 greater arc injuries. Suspicion for the injury and careful interpretation of the radiographs should prevent any delay in diagnosis. Perilunate injuries tend to occur as a result of high-energy trauma, however, and patients may have more serious injuries that distract the physician from the injured wrist. Such a scenario also may contribute to a delay in the diagnosis of a perilunate injury.

Initial Treatment

In the acute trauma setting, an urgent reduction of the carpus should be performed. Closed reduction in the emergency department is the best way to restore carpal alignment initially and should be attempted. A closed reduction is usually obtainable and allows definitive surgery to be delayed to an optimal time and place.

Authors’ Preferred Methods

Lesser Arc Injuries

Pure perilunate injuries are probably best treated with combined volar and dorsal approaches, especially in stage IV injuries (lunate dislocation). When a volar approach is made, open reduction of the dislocated lunate is performed, and complete carpal tunnel release is provided as an additional benefit. The volar approach also makes it possible to repair the torn volar capsule, which is a principal site of injury in these cases. The volar capsule is repaired with 3-0 nonabsorbable sutures.

The dorsal approach is made through a longitudinal midline incision at Lister’s tubercle, and an approach is made to the wrist through the third dorsal extensor compartment. The dorsal capsule is usually torn, and the arthrotomy is frequently through this rent. The joint is inspected to appreciate the scope of damage, and a complete débridement of any tiny loose osteocartilaginous fragments is performed.

The position of the lunate is reduced to its position on the radius, and if necessary, a temporary K-wire is inserted between radius and lunate to secure its position before reducing the adjacent joints. Next, the scaphoid is reduced to the lunate. A K-wire may be inserted into the scaphoid as a joystick to facilitate derotation and allow reduction of the scapholunate interval. The scaphoid is usually in a flexed orientation, and the K-wire joystick can help to rotate the scaphoid into an extended position alongside the lunate. Next, the scapholunate interval is reduced, and temporary use of bone reduction forceps may be needed to maintain alignment while inserting internal fixation. The correct alignment should result in excellent apposition of the dorsal and distalmost fibers of the scapholunate interosseous ligament. The preliminary radiograph should show no residual intercarpal gap and restoration of the scapholunate angle (30 to 60 degrees). When the position is confirmed to be acceptable, the scapholunate interval is stabilized with two 0.062-inch K-wires inserted from the scaphoid into the lunate. An additional 0.062-inch K-wire is inserted from the distal scaphoid into the capitate to prevent rotary subluxation of the scaphoid and subsequent loss of reduction (Fig. 43-6).

FIGURE 43-6 Open reduction and internal fixation of lesser arc perilunate injury. A and B, This is a purely ligamentous injury with midcarpal dislocation noted on the lateral view and triangular shape of the lunate seen on the anteroposterior view. C and D, Postoperative x-rays after open reduction and internal fixation with Kirschner wires. The scaphocapitate wire is helpful to prevent palmar rotation of the scaphoid. A suture anchor was placed in the lunate to augment scapholunate ligament repair.

If the scapholunate ligament has good residual substance, a ligament repair is attempted. The repair may be made through drill holes or augmented with suture anchors. If the ligament is shredded or of otherwise poor quality, however, no attempt for direct repair is made, and the ligament is allowed to heal spontaneously.

After scapholunate repair, the lunotriquetral joint is addressed. The triquetrum must be simultaneously reduced to the lunate and to the spiral groove of the hamate. A dental pick is used to facilitate the reduction of the triquetrum as it is coaxed toward the apex between the lunate and hamate bones. When reduced, the triquetrum is stabilized with two 0.062-inch K-wires inserted from the ulnar border of the wrist and passing across the lunotriquetral and triquetral-hamate joints.

Greater Arc Injuries

Open reduction and internal fixation (ORIF) of perilunate fracture-dislocations is typically performed through an exclusively dorsal approach to the wrist. The dorsal approach provides all the necessary exposure to address fully the pathology present, and stable fixation of the scaphoid fracture sufficiently addresses the injury to the radial side of the wrist. A palmar approach is used only to address median nerve compression if present or to reduce the lunate if dislocated into the carpal tunnel.

Typically, in greater arc injuries, the scapholunate ligament is intact with an associated midwaist fracture of the scaphoid and lunotriquetral dissociation. When the position of the lunate and proximal pole of the scaphoid is reduced to the appropriate position on the radius, the scaphoid can be repaired with internal fixation.

The scaphoid typically is repaired with a headless self-compressing screw if possible. The screw is inserted into the scaphoid fracture antegrade through the proximal pole; excellent fixation is typical (Fig. 43-7). The scaphoid fracture may be comminuted or very proximal, however, making it difficult to obtain solid fixation. K-wire fixation is acceptable in these situations, and bone grafting from the distal radius should be obtained if necessary.

FIGURE 43-7 A to D, Open reduction and internal fixation of greater arc perilunate fracture-dislocation. A headless self-compressing cannulated screw is inserted into the scaphoid dorsally and antegrade at the proximal pole. Kirschner wires are used to stabilize the lunotriquetral interval for healing of the lunotriquetral ligament and triquetral fracture.

Occasionally, the proximal pole of the scaphoid is a free fragment with simultaneous rupture of the scapholunate ligament. Herzberg and colleagues¹ reported that simultaneous scaphoid fracture and scapholunate ligament tear occurred in 3.8% of cases. In these situations, it is probably best to use K-wire fixation for the scaphoid fracture because the presence of a screw in the scaphoid makes scapholunate ligament repair more difficult. After wire fixation of the scaphoid, the scapholunate joint is reduced and stabilized as noted in the technique for lesser arc perilunate repair.

When the capitate is fractured, the open reduction typically proceeds with this bone first (Fig. 43-8). The head of the capitate is typically a free osteocartilaginous fragment that has rotated 180 degrees. The fragment can be derotated and repaired with a headless compression screw or with K-wire fixation. Bone grafting from the distal radius may be required. Fractures of the radial or ulnar styloids are usually avulsion fractures that are treated with direct open reduction and pin fixation, although screw fixation also may be considered if the fragments are large.

FIGURE 43-8 A to D, Greater arc perilunate injury with scaphoid and capitate fractures (scaphocapitate syndrome). Note the fracture of the capitate and the malrotation of the fragment. Open reduction and internal fixation is performed through a dorsal approach with headless cannulated screw fixation of the scaphoid and capitate. The lunotriquetral joint is stabilized with Kirschner wires after open reduction.

Finally, the lunotriquetral joint is reduced and stabilized. In perilunate fracture-dislocation, the lunotriquetral ligament is usually disrupted without fracture, and the lunotriquetral joint is reduced and pinned with 0.062-inch K-wires as noted in the technique of lesser arc perilunate repair. Fracture of the triquetrum may occur in greater arc injury, however. In such cases, the triquetral fracture can be treated with pin or screw fixation depending on the size of the fracture fragments.

Postoperative Care

Pins are cut below the skin, and the wrist is immobilized initially in a short arm splint and bulky hand dressings until suture removal. A short arm cast is used until 10 weeks postoperatively, at which time the pins are removed. Careful surveillance of the scaphoid fracture is required because of the possibility of delayed union or nonunion. The patient is enrolled in an occupational therapy program after cast removal with gradual progression of activities. Twelve to 18 months may be required until the final result is obtained, when pain resolves, and motion and strength have been optimized.²⁵

Outcomes

Patients who undergo timely ORIF for perilunate injuries have the most successful outcomes. Most authors agree that the expected recovery of wrist range of motion after ORIF is about a 110-degree arc of flexion and extension with return of approximately 75% of grip strength.³ Although outcome studies of perilunate injuries have shown suboptimal assessment scores consistent with loss of function,^25,26 there also are numerous reports of acceptable patient satisfaction with regards to pain relief and function after ORIF. Hee and colleagues²³ reported 62% excellent and good results in the outcome of 15 patients treated with ORIF. Sotereanos and associates²⁵ noted that despite loss of motion and grip, 82% of patients were satisfied with the procedure, but only 45% returned to work. Other series report a much more optimistic prognosis for return to work after perilunate ORIF, including a return to employment rate of 80% to 100% with 66% to 92% able to return to their preinjury occupation.^11,19,24,26

Souer and coworkers¹⁴ compared K-wires with temporary intercarpal screws in 18 patients (9 treated with 3-mm cannulated intercarpal screws and early mobilization at 3 weeks, and 9 treated with intercarpal K-wires and casting for 3 months). The intercarpal screws were removed an average of 5 months and the K-wires an average of 3 months after the initial procedure. Four patients (two in each cohort) had wrist arthrodesis with poor results. Among the 14 remaining patients, the final flexion arc was 97 degrees for patients treated with screw fixation compared with 73 degrees for patients treated with K-wires. The authors concluded that the results of treatment with temporary screws were comparable to the results of treatment with temporary K-wires. The appeal of temporary screw fixation lies in the ability to begin mobilizing the wrist within a few weeks and the absence of pin-related complications. Although superior wrist motion was obtained in the intercarpal screw group, the numbers were too small to provide any definitive conclusions.¹⁴

Delay to definitive surgical treatment is one of the most significant variables that adversely affect the outcome of perilunate injuries. This is significant because there is frequently a delay in the diagnosis and treatment of perilunate injuries, which may result in a poor outcome. Herzberg and colleagues¹ noted that patients treated with ORIF within 1 week had superior Mayo wrist scores compared with patients treated later, with only fair to poor results reported in patients treated after 45 days. Open injuries also are likely to have a poor outcome. The adverse results after open perilunate injuries is probably a reflection¹ of the more serious initial injury to the wrist, including the greater magnitude of injury to joint surfaces and ligaments.

Poor results in most series have followed cases with residual wrist instability, ulnar translocation of the carpus, and scaphoid nonunion. Despite the serious injury to the wrist in the vicinity of the lunate, reported cases of Kienböck’s disease and lunate fragmentation are rare after perilunate wrist injury. The reported incidence of post-traumatic arthrosis at late follow-up is high, however, and is usually identified in the midcarpal joint. The incidence of post-traumatic arthritis after treatment of perilunate injuries is reported to range from 50% to 100% in the literature.^1,14,16,26

Late Presentation

Too many perilunate injuries are missed at initial presentation, and this creates a very difficult situation for the treating surgeon. Suboptimal results can be expected in these cases, but open reduction should be performed if possible. It is unknown how late in presentation that ORIF can be performed, but there are reports³ of successful open reduction performed up to 35 weeks postinjury. Some authors have recommended the use of preoperative or intraoperative traction with external fixation to facilitate delayed open reduction.³

Siegert and colleagues²⁷ and others evaluated 16 perilunate dislocations and fracture-dislocations with an average delay to surgery of 17 weeks. Despite the delay in presentation, they were able to perform open reduction in six of these cases with acceptable outcomes. When open reduction was impossible, the authors resorted to lunate excision, proximal row carpectomy, or wrist arthrodesis as primary treatment. Siegert and colleagues²⁷ noted that patients treated with simple lunate excision had poor results, and this was not recommended as primary treatment of chronic perilunate injuries.