Posterior Elbow Dislocation

Etiology

A posterior elbow dislocation often occurs when a person falls on an outstretched hand, posteriorly directed force at the elbow joint causes dislocation at the ulnohumeral and radiocapitellar articulations. Valgus force may induce the commonly seen posterolateral elbow dislocation.   [3][4][5]

Anterior elbow dislocations occur when the elbow is flexed, and there is a direct blow on the posterior aspect of the elbow.

Epidemiology

Elbow dislocation is the most common joint dislocation in pediatric patients and the second most common in adult patients. The incidence is reported at 6 to 13 per 100,000 persons per year. The injury more often occurs in adolescent male athletes. Specifically, varsity football and wrestling participants are particularly susceptible to this injury.  Posterior elbow dislocations comprise 90% of all elbow dislocations.[6][7][8]

Pathophysiology

Considering elbow anatomy and the likely mechanism of injury causing an elbow dislocation can help one understand the pathophysiology associated with this particular injury. During a posterior elbow dislocation, the shearing forces causing the injury may cause associated radial head, radial neck or coronoid process fractures. The medial collateral and lateral collateral ligaments provide support to the elbow joint in addition to its bony anatomy. The LCL is often disrupted when an elbow dislocation occurs; the MCL is the last soft tissue structure injured as the ulna is displaced. Often, the flexor-pronator mass may be ruptured, and occasionally the brachialis may be injured.

The anterior compartment of the elbow encompasses the brachial artery and ulnar and median nerves. These structures are particularly vulnerable to injury because the anterior compartment is often disrupted during posterior dislocation. The ulnar nerve may become entrapped as it passes posteriorly around the medial epicondyle. The brachial artery and median nerve travel closely to one another and injuries are often seen in both these structures simultaneously.

Anterior dislocations are often associated with olecranon fractures.  These dislocations may also disrupt the posterior elbow compartment which contains the radial nerve and insertion of the triceps muscle.

History and Physical

All patients experiencing traumatic injury should first be assessed head to toe for any life or limb threatening injuries first. Obvious bony deformities may distract both the patient and the practitioner from more serious traumatic injuries. After the patient has been cleared of other significant injuries, attention can be turned to the affected extremity.

The initial history should consist of the mechanism of injury and the duration of the injury until initial presentation. The patient should be asked if this is a first-time occurrence or if there have been previous elbow injuries in the past. A physician should review associated symptoms suggesting a neurovascular compromise and inquire about numbness, tingling or coolness of the distal extremity.

The physical examination should begin with an inspection of the elbow joint looking for swelling, deformity or bruising. Posterior elbow dislocations often present with an upper extremity that is flexed and appears shortened. Anterior elbow dislocations are held in extension, and the upper extremity appears elongated. Specific attention should be paid to looking for open wounds which would suggest a complex dislocation. The functionality of the elbow joint should be assessed by observing a range of motion. It is also important to evaluate the remainder of the affected extremity and nearby joints for associated injury. Particular attention should be paid to the distal radioulnar joint for tenderness which can indicate disruption of the intraosseous ligament, eponymously referred to as an Essex-Lopresti lesion.

The most common neurovascular structures injured during an elbow dislocation include the brachial artery and the ulnar and median nerves. Perfusion can be assessed by palpating the radial and ulnar pulses and looking for a brisk capillary refill. Median nerve sensation can be assessed by a light touch of the palmar aspect of the thumb and second finger. Median motor function is tested by observing the strength of thumb opposition. A light touch on the palmar aspect of the fourth and fifth fingers can assess ulnar sensation. The ulnar motor function is tested by observing the strength of finger abduction and adduction.  Historical or physical findings concerning for neurovascular compromise must also raise the suspicion for compartment syndrome.

Evaluation

Initial evaluation of a suspected elbow dislocation should begin with anterior-posterior and lateral plain radiographs with attention to joint congruency and potential fractures. Oblique views may be best to evaluate for periarticular fractures. Computerized tomography may be considered if there is a concern for a complex injury or to identify periarticular fractures not easily seen on plain radiographs. Repeat radiographs to ensure adequacy and maintenance of reduction should be obtained after manipulation. Attention should be paid to normal radiocapitellar alignment in values to demonstrate adequate reduction.

Treatment / Management

Initial treatment of simple, closed posterior elbow dislocations is closed reduction. Some complex elbow dislocations may initially be treated with closed reductions; however, associated fracture implies significant soft tissue damage and likely persistent instability which may require open reduction and internal fixation to improve outcomes. Open dislocations will require extensive washout during an open reduction. Any dislocation with signs of neurovascular compromise requires immediate closed reduction.[9][2]

There are two common approaches to the reduction of a posterior elbow dislocation. It is recommended the first technique is attempted in the prone position. With the patient laying down the affected arm is abducted with an elbow on the edge of the cart. The wrist is then grasped and the forearm placed in slight supination while gentle traction is applied. The coronoid process must be distracted and disengaged from the olecranon fossa. Once this has been accomplished downward pressure with the other hand on the olecranon should reduce the dislocation with the operator feeling a confirmatory clunk. A two-person technique is also described where one operator applies downward traction at the wrist, and other applies the downward force onto the olecranon with both their thumbs.

The alternative method is performed with the patient seated or lying supine on the cart. An assistant stabilizes the affected humerus while the operator flexes the elbow, supinates the wrist slightly and applies distal and downward traction at the wrist with one hand. The other hand is placed just distal to the elbow on the volar aspect of the forearm applying slow, gentle inline traction until the confirmatory clunk is appreciated.

Following reduction of the dislocation, a neurovascular examination should be performed to identify improvement in any previous neurovascular symptom or a new symptom that may have manifested following the reduction.  The elbow should be held in 90 degrees of flexion for 5 to 10 days followed by an active range of motion. Earlier range of motion has demonstrated better physical outcomes. Dislocations that appear more unstable may require up to 3 weeks of splinting and a specific range of motion plan. Post-reduction films should be obtained.

Differential Diagnosis

• Olecranon bursitis

• Olecranon stress fracture

• Osteoarthritis

• Posterior impingement 

• Tricepstendinopathy