Anterior Elbow Dislocation

Etiology

Falling onto an outstretched arm with an anterior force on the proximal ulna leads to an anterior elbow dislocation.

This injury and its complications are best understood after reviewing pertinent anatomy. The elbow is a joint made up of the articulation between three bony structures, the humerus, ulna, and radius. The distal humerus is the most proximal aspect of the elbow. The distal humerus flares out medially and laterally making the medial and lateral epicondyles. The trochlea and capitellum make up the distal joint surface of the humerus, articulating with the greater sigmoid notch of the proximal ulna and the radial head respectively.[3]

The olecranon is the posterior portion of the proximal ulna and forms the posterosuperior part of the greater sigmoid notch.[3] The coronoid process of the proximal ulna forms the anterior portion of the notch and is where the brachialis and anterior medial collateral ligament attach. Laterally, the proximal ulna has the lesser sigmoid notch also called the radial notch where the proximal radius articulates.  

The soft tissue surrounding the elbow joint contributes to the stability of this three-part joint. The annular ligament is a ligament that surrounds the radial head and is an insertion site of the joint capsule. The joint capsule also inserts onto the anterior aspect of the coronoid. Posteriorly, the joint capsule attaches to the olecranon. The capsule contributes to the varus-valgus stability of the elbow when in extension.[4] Varus-valgus stability of the elbow is also reinforced by the medial and lateral collateral ligaments.

The medial ulnar collateral ligament contributes to the valgus stability of the elbow and consists of the anterior, posterior, and transverse bands. The medial collateral ligament originates from the medial epicondyle and inserts at the base of the coronoid.[5]

The lateral collateral ligament contributes to the varus stability of the elbow and also consists of three components: the lateral ulnar collateral ligament, the annular ligament, and the radial collateral ligament.[3] The lateral ulnar collateral ligament inserts on the lateral epicondyle and the supinator crest on the proximal ulna, giving the elbow posterolateral stability. The annular ligament wraps around the radial head and attaches to the radial notch on the ulna, stabilizing the radioulnar joint. The radial collateral ligament also stabilizes the radial head by attaching to the lateral epicondyle and the annular ligament.

There are multiple neurovascular structures that cross the elbow joint that are at risk for injury during an elbow dislocation. The brachial artery crosses the elbow joint anteriorly before branching into the radial and ulnar artery distally in the forearm. The median nerve runs alongside the brachial artery crossing the elbow joint anteriorly. The radial nerve crosses the elbow joint laterally along the lateral epicondyle, where the ulnar nerve crosses the elbow medially along the medial epicondyle.

A strong anterior force to the posterior aspect of the flexed elbow is the most common mechanism of injury in an anterior elbow dislocation.[6] Put simply, the basic mechanism of anterior elbow dislocation is hyperextension.

With anterior elbow dislocations, the olecranon is commonly fractured. The anterior force on the flexed elbow causes the olecranon to be levered within the olecranon fossa and fractured. The continuation of the anterior force displaces the more distal aspect of the ulna anteriorly, leaving the fractured olecranon fragment behind.[7]

Epidemiology

Anterior dislocation of the elbow is a rare injury making up approximately 0-2.6% of all elbow dislocations.[8] Anterior elbow dislocations are rare due to the high force and position of the elbow necessary to cause this injury.

History and Physical

Anterior elbow dislocations, like all elbow dislocations, occur after a traumatic event. Patients will typically have a history of some mechanism, causing them to fall onto their outstretched arm or more severe trauma to the arm like a motor vehicle accident. Patients will complain of severe pain to the injured extremity and will be unable to move the injured elbow. Also, patients may complain of a noticeable deformity of the affected elbow depending on body habitus and the nature of the dislocation.

While obtaining the history, it is important to ask the patient if they have previously dislocated or had any history of injury to the dislocated elbow. The provider should also ask the patient if they are having any new onset of numbness, tingling, or weakness in the injured extremity as damage to neurovascular structures can be associated with anterior elbow dislocations. Neurovascular compromise can affect the urgency of reduction and operative fixation. Another important aspect before moving on to the physical evaluation is to ask if the patient has had any head trauma, loss of consciousness, or have any other areas of pain as this will influence what further workup will need to be done. Finally, each patient should be asked to provide their complete medical history, congenital deformities, and medications that can affect their diagnosis and treatment moving forward.

Evaluation

The initial evaluation should begin with an inspection of the patient and a physical exam. Clinicians should evaluate for additional injuries visually and by palpating along with other bones and joints. On evaluation, the injured extremity should be inspected for open fractures, swelling, skin changes, and neurovascular status. Palpation along the injured extremity should be done to make sure all compartments are compressible. If a compartment is too full to compress, then the examiner should be concerned for compartment syndrome, which is an operative emergency. If the patient has compartment syndrome, their neurovascular status will be diminished. Vascular status can be examined by observing the color of the extremity, palpating the temperature of the skin, the radial and ulnar pulses at the wrist, and capillary refill of the fingers. Neurological status can be evaluated by checking for sensation along the length of the extremity and having patients perform tasks to demonstrate motor function. Compartment syndrome, an open fracture, or neurovascular compromise all warrant emergent evaluation by an orthopedic surgeon.

The most common nerves injured during an elbow dislocation are the median and ulnar nerves. The median nerve sensation can be evaluated by light touch to the palmar aspect of the thumb and index finger. The motor function of the median nerve can be tested by observing the strength of thumb opposition.[9] Ulnar nerve sensation can be determined by light touch over the palmar aspect of the fourth and fifth digits. The motor function of the ulnar nerve is assessed by observing the strength of abduction and adduction of the fingers.

After the physical exam, radiographic images should be obtained. Initial radiographic evaluation of the injured extremity should begin with anterior-posterior, lateral, and oblique views. It is also important to get anterior-posterior and lateral X-rays of the forearm, wrist, and shoulder to evaluate for any other injuries.

Treatment / Management

Initial management should always be closed reduction. The reduction can help decrease pain and swelling as well as taking pressure off of soft tissue and neurovascular structures. Anterior elbow dislocations require modification to the typical elbow reduction maneuvers.[10]

In most cases, the patient will need intravenous sedation to relax the muscles allowing for proper manipulation for reduction. Once the patient is adequately sedated, traction should be applied to the arm. Ideally, there are two providers pulling traction, one on the forearm with the other pulling counter traction on the humerus. For an anterior elbow dislocation, the reduction is performed by flexing the elbow while pulling traction and applying a downward force on the proximal forearm.[11] After reduction, the stability of the elbow should be tested with a range of motion and varus and valgus stress. An unstable elbow after reduction is more likely to need operative intervention than a stable elbow. The neurovascular status of the extremity should also be reevaluated after reduction. A posterior, long arm splint should then be applied with the elbow flexed at ninety degrees. After the splint is in place, post-reduction radiographs should be taken to ensure the elbow is adequately reduced.(B3)

The patient should remain splinted and follow up in five to ten days from the time of reduction.[9] At that point, the patient’s elbow should be reexamined for stability and neurovascular status. If the elbow remains unstable or demonstrates a fracture on x-ray, the patient will require operative intervention. If the elbow is stable on the exam, then the patient may begin an early range of motion to prevent stiffness. Elbows tend to get stiff if they are immobilized for more than three weeks. After about twenty-one days of immobilization, it becomes very difficult for the patient to regain the full range of motion of their elbow.

Differential Diagnosis

Anterior elbow dislocations tend to be a clinical diagnosis and are confirmed by radiographic images. However, when a patient presents after trauma with elbow pain, there are other diagnoses that need to be considered. A number of injuries can present as elbow pain, such as a distal humerus fracture, fracture of the radial head, fracture of the olecranon, or purely ligamentous injuries. It is important to approach each patient with a list of differential diagnoses and to use the history, physical exam, and imaging modalities to lead to an accurate diagnosis.

Prognosis

The most common lifelong negative outcome after an anterior elbow dislocation is the loss of terminal extension. Patients who have a simple anterior elbow dislocation have a strong chance of regaining full range of motion after recovery. However, patients with injuries that require periods of greater than three weeks of immobilization, such as complex anterior elbow dislocations or those with neurovascular injuries, tend to lose terminal extension. It is not uncommon for patients to lose up to ten to fifteen degrees of terminal extension after an elbow dislocation.[12]

Complications

Common complications associated with anterior elbow dislocations are the same as those associated with elbow dislocations in general. Stiffness with a range of motion, and more specifically loss of terminal extension, is the most common complication after an elbow dislocation. This occurs with prolonged immobilization, typically greater than three weeks, and can be improved by physical therapy focusing on a range of motion.

Persistent elbow instability is another complication that can occur after an elbow dislocation. Varus instability is the most common and is due to insufficiency of the lateral collateral ligament. Lateral collateral ligament insufficiency can be treated by splinting in pronation but may require surgical repair.[12]

Neurovascular injury can be a complication of an anterior elbow dislocation. The three neurovascular structures of the elbow most commonly injured are the ulnar nerve, median nerve, and brachial artery. Ulnar nerve neuropraxia is the most common injury due to stretching of the nerve during the dislocation, with median nerve neuropraxia following second to it. Neuropraxias are initially managed by observation and typically resolve over time. Median nerve entrapment can occur in the instance where there is a fracture, and this warrants surgical exploration of the nerve.[1] Finally, injury to the brachial artery is a rare occurrence usually associated with severe, open fracture-dislocations. Pulses typically return after reduction, however in the instance where they do not further workup and surgical intervention is required.[13]