Introduction

The elbow is the second most commonly dislocated major joint in the body after the shoulder, with an annual incidence of 6.1 dislocations per 100 000 population. Elbow dislocations constitute approximately 10–25% of all elbow injuries and approximately 6.8% of all treated fractures or dislocations.^1–3

The most common mechanism of injury is a fall onto the outstretched hand in which the elbow is extended and the shoulder is abducted. This is most often seen with high-energy mechanisms such as motor vehicle accidents and sports injuries. The median age for an elbow dislocation is 30 years.³ Almost all complete elbow dislocations without large periarticular fractures cause rupture of the medial and lateral collateral ligaments. Fortunately, the vast majority of these injuries can be treated conservatively without surgical intervention.

Elbow dislocations are classified according to the direction of forearm displacement relative to the distal humerus. Most consist of posterior or posterolateral displacement although less commonly lateral and anterior displacement of the forearm can also occur. Elbow dislocations can also be classified as simple or complex, and this is determined by the presence or absence of concomitant bony fractures. Simple dislocations are characterized by the absence of associated fractures, while complex dislocations are associated with large periarticular fractures. It should be noted that although pre- and post-reduction radiographs reveal large periarticular fractures in 12–60% of cases (complex elbow dislocations), operative exploration has documented unrecognized soft tissue injuries in nearly 100% of elbow dislocations.⁴ The most common complex dislocation pattern is an acute elbow dislocation with a fracture of the radial head. However, complex elbow dislocations encompass a wide range of bony and ligamentous injuries that result in elbow instability and usually require surgical intervention. As a result, the rest of this chapter will focus on the anatomy, diagnosis, treatment and outcomes of simple elbow dislocations.

Background/aetiology

The elbow has 2 degrees of freedom: flexion/extension and pronation/supination. Elbow motion follows a somewhat regular course from flexion to extension with the axis of rotation being primarily from the centre of the capitellum to the anterior–inferior medial epicondyle. This axis does, however, shift a few millimetres as the elbow goes from flexion to extension, resulting in the elbow having a moving centre of rotation. As such, the elbow is not, strictly speaking, a pure hinge joint.

The elbow has both static and dynamic constraints. The three primary static constraints to elbow instability are the ulnohumeral articulation, the anterior bundle of the medial collateral ligament and the lateral collateral ligament complex. The secondary static constraints include the radial head, the common flexor origin and the common extensor origins. With all three primary constraints intact, the elbow joint is stable. If the coronoid process is fractured, the radial head becomes a critical stabilizer. Therefore, the radial head must not be removed when a dislocated elbow is associated with a fractured coronoid process. There are also multiple dynamic constraints to elbow instability. The biceps and triceps maintain ulnohumeral contact, the flexor/pronator mass supports the medial collateral ligament, and the common extensor origin, extensor carpi ulnaris and anconeus help stabilize the lateral collateral ligament complex.

The main soft tissue stabilizers are the two collateral ligament complexes and the anterior capsule. The anterior capsule is relatively thin, and although it contributes to stability the collateral ligaments are the primary soft tissue stabilizers of the elbow. The lateral collateral ligament complex originates on the lateral epicondyle at the point of the axis of rotation. In contrast, the medial collateral ligament complex has two discreet components, neither of which is exactly at the axis of rotation. The anterior bundle of the medial collateral ligament is tight in extension, while the posterior bundle is tight in flexion.

The anterior bundle is the main stabilizer of the medial part of the elbow as it connects the anterior inferior aspect of the medial epicondyle to the sublime tubercle on the ulna. The posterior bundle, although also originating from the antero-inferior aspect of the medial epicondyle, has a broad insertion along the medial aspect of the ulna, extending toward the olecranon tip.

The lateral collateral ligament complex comprises the radial collateral ligament, the annular ligament and the lateral ulnar collateral ligament. The radial collateral ligament extends from the lateral epicondyle to the annular ligament. The annular ligament is a very broad, thick structure that encircles the radial head. The lateral ulnar collateral ligament extends from the epicentre of the lateral epicondyle to the crista supinatoris on the lateral edge of the ulna. The interplay of the radial collateral ligament, the lateral ulnar collateral ligament and the annular ligament provide stability to the lateral aspect of the elbow.

Dunning et al performed a biomechanical cadaveric study in which sequential sectioning of the radial collateral and lateral ulnar collateral ligaments was performed in 12 cadaveric elbows. After each stage of the sectioning protocol, internal/external rotation and varus/valgus laxity were evaluated with an electromagnetic tracking device. They noted no significant difference in the magnitude of internal/external rotation and varus/valgus laxity of the ulna, with only the radial collateral or lateral ulnar collateral ligament intact. It was therefore concluded that, when the annular ligament is intact, either the radial collateral ligament or the lateral ulnar collateral ligament can be transected without inducing posterolateral rotatory instability of the elbow.⁵ The results of this study suggest that surgical approaches which violate only the anterior or posterior half of the lateral collateral ligament complex should not result in posterolateral rotatory instability of the elbow. Therefore a surgical approach to the radial head, for example, can transect the radial collateral ligament and not result in instability. Similarly, a surgical approach that violates the lateral ulnar collateral ligament would also not result in instability provided the radial collateral ligament complex was intact.

It is often difficult to separately dissect out each of the components of the lateral ligament complex, and it is probably more appropriate to refer to it as the lateral ligament complex rather than specifying any individual component. The lateral collateral ligament complex resists varus forces, which are the predominant forces on the elbow joint during activities of daily living. The lateral collateral ligament complex is also further from the varus/valgus axis of the elbow compared to the medial collateral ligament and has a longer origin to insertion distance because it has to curve around the radial head. As such, there is potentially greater translation of the lateral collateral ligament complex with injury or dysfunction. The medial collateral ligament transmits little stress during most activities of daily living.

Some osseous relationships have also been described in the context of simple elbow dislocation. Wadstrom et al evaluated the anatomical relationship of the semilunar notch of the ulna in patients with elbow dislocation. They compared lateral radiographic views of 100 patients with elbow dislocations with radiographs from 150 patients without dislocation or other radiographic pathology. They noted a lower coronoid process as well as a more prominent tip of the olecranon in the radiographs of patients who had sustained an elbow dislocation. They concluded that the dislocation mechanism was at least partially hyperextension, with the tip of the olecranon acting as the pivot point.⁶

Presentation, evaluation and initial treatment

Patients with acute elbow dislocation tend to present with pain, soft tissue swelling and an obvious deformity of the elbow (Fig. 24.1). A thorough neurovascular examination of the upper extremity should always be performed. Closed elbow dislocations are rarely associated with vascular injury, and only a handful of brachial artery injuries associated with closed simple elbow dislocation have been reported.⁷ In open dislocations, however, the brachial artery is more often disrupted due to the forcible hyperextension of the elbow. Median and/or ulnar nerve injury is also commonly associated with such injuries. Neurapraxia has been reported to occur in approximately 20% of elbow dislocations and usually involves the anterior interosseous branch of the median nerve and/or the ulnar nerve. Ulnar nerve palsy has been reported in 14% of adult elbow dislocations, and the incidence is much higher in paediatric elbow dislocations with an associated medial epicondyle fracture. Most neurological deficits are transient, but entrapment of the median nerve within the elbow joint following reduction is relatively common in paediatric elbow dislocations and if not recognized will cause permanent disability.⁸ The wrist and shoulder joints should be carefully examined to rule out a concomitant upper extremity injury, which have been noted in 10–15% of acute elbow dislocations.⁹ Of note, the distal radio-ulnar joint (DRUJ) and forearm interosseous membrane should always be examined for tenderness and instability to rule out an associated interosseous membrane disruption.

Figure 24.1 Clinical photograph (A) and lateral radiograph (B) of a posterolateral elbow dislocation. Note the obvious deformity and prominence over the posterior elbow.

Courtesy of Glen Ross MD, New England Baptist Hospital.

Anteroposterior (AP) and lateral radiographs are normally sufficient to allow diagnosis of the dislocation. The films should be examined to determine the direction of forearm displacement so that the injury can be appropriately classified. In addition, a careful assessment must be made to identify whether there is any evidence of bony injury. Standard preoperative radiographs sometimes make it difficult to diagnose a medial coronoid fracture. If the initial radiographs show any small pieces of bone, it should not be assumed that this is bone from the radial head as the fragments may represent a medial coronoid fracture. If a medial coronoid fracture is missed and the elbow assumes a subluxed position, then an arthritic ulnohumeral articulation will result, which can be very difficult to treat if diagnosed late. If there is doubt as to whether bony fragments are present a CT scan following reduction of the dislocation is appropriate.

Simple elbow dislocations are acutely treated with reduction. Reduction requires adequate muscular relaxation and appropriate analgesia. This is usually done in the emergency department with intravenous or intramuscular medication. The acute treatment of the posterior or posterolateral dislocated elbow in the emergency department is to place the patient in the prone position and to supinate the patient’s arm. With the proximal part of the arm over a padded bolster on the edge of the examining table, pressure is applied to the olecranon tip in a distal and posterior direction as the elbow is gradually flexed, resulting in reduction. Muscular relaxation is necessary for adequate reduction, and the quality of the reduction often provides a clue to postreduction stability. A palpable reduction ‘clunk’ is a favourable sign of joint stability (Fig. 24.2).¹⁰

Figure 24.2 AP (A) and lateral (B) radiographs of a simple posterolateral elbow dislocation. The elbow was subsequently reduced under muscular relaxation and the assistance of fluoroscopy. Anteroposterior (C) and lateral (D) radiographs demonstrate a concentric reduction with the elbow flexed to 90° in a plaster splint.

Following successful reduction, the range of motion and stability of the elbow are assessed. The vast majority of simple elbow dislocations are unstable to valgus stress, and this is best tested in pronation to lock the lateral side. The elbow is generally stable in 90° or more of flexion. It is essential, however, to evaluate the elbow in a position of near or full extension to determine the tendency for redislocation. If the elbow is unstable in this position, this signifies a potentially unstable joint. If elbow instability occurs in 30° of flexion, the forearm can be placed in maximum pronation to maximize the stress on the medial collateral ligament. This results in reduction of the posterolateral subluxation. As a result, the elbow should be immobilized in pronation in this situation.