Elbow Dislocation
EPIDEMIOLOGY
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Elbow dislocation accounts for 11% to 28% of elbow injuries.
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Posterior dislocation is most common, accounting for 80% to 90% of all elbow dislocations.
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Annual incidence of elbow dislocations is 6 to 8 cases per 100,000 population per year.
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Simple dislocations are purely ligamentous.
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Complex dislocations are those that occur with an associated fracture and represent slightly less than 50% of elbow dislocations.
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Highest incidence occurs in the 10- to 20-year-old age group and is associated with sports injuries; recurrent dislocation is uncommon.
ANATOMY
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The elbow is a “modified hinge” joint with a high degree of intrinsic stability owing to joint congruity, opposing tension of triceps and flexors, and ligamentous constraints.
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Three separate articulations are:
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Ulnotrochlear (hinge)
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Radiocapitellar (rotation)
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Proximal radioulnar (rotation)
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Stability (Fig. 18.1)
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Anterior-posterior: trochlea-olecranon fossa (extension); coronoid fossa, radiocapitellar joint, biceps-triceps-brachialis (flexion).
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The anterior joint capsule is also felt to play a role in ulnohumeral stability.
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Valgus: The medial collateral ligament (MCL) complex
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Anterior band is the primary stabilizer in flexion and extension.
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Anterior capsule and radiocapitellar joint function in extension.
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Varus: The lateral ulnar collateral ligament is static, and the anconeus muscle is dynamic stabilizer.
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Function of the MCL
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Primary medial stabilizer, especially the anterior band.
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Full extension provides 30% of valgus stability.
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Ninety degrees of flexion provides >50% of valgus stability.
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Resection of anterior band will cause gross instability except in extension.
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Lateral ligaments
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Prevent posterior subluxation and rotation of the ulna away from the humerus with the forearm supination (posterolateral rotatory instability).
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Normal range of motion: 0 to 150 degrees flexion, 85 degrees supination, and 80 degrees pronation.
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Functional range of motion (ROM) requires: a 100-degree arc, 30 to 130 degrees flexion, 50 degrees supination, and 50 degrees pronation.
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More recent reports suggest increased ROM is needed to perform contemporary activities of daily living such as talking on a cell phone or using a computer mouse and keyboard.
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MECHANISM OF INJURY
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Most commonly caused by a fall onto an outstretched hand or elbow, resulting in a levering force to unlock the olecranon from the trochlea combined with translation of the articular surfaces to produce the dislocation.
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Posterior dislocation: This is a combination of elbow hyperextension, valgus stress, arm abduction, and forearm supination.
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Anterior dislocation: A direct force strikes the posterior forearm with the elbow in a flexed position.
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Most elbow dislocations and fracture-dislocations result in injury to all the capsuloligamentous stabilizers of the elbow joint. The exceptions include transolecranon fracture-dislocations and injuries with fractures of the coronoid involving nearly the entire coronoid process.
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The capsuloligamentous injury progresses from lateral to medial (Hori circle) (Fig. 18.2); the elbow can completely dislocate with the anterior band of the MCL remaining intact. There is a variable degree of injury to the common flexor and extensor musculature.
CLINICAL EVALUATION
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Patients typically guard the injured upper extremity, which shows variable gross instability and swelling.
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A careful neurovascular examination is essential and should be performed before radiography or manipulation.
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Following manipulation or reduction, repeat neurovascular examination should be performed to assess neurovascular status.
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Serial neurovascular examinations should be performed when massive antecubital swelling exists or when the patient is felt to be at risk for compartment syndrome.
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Angiography may be necessary to evaluate vascular compromise.
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Following reduction, if arterial flow is not reestablished and the hand remains poorly perfused, the patient should be prepared for arterial reconstruction with saphenous vein grafting.
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Angiography should be performed in the operating room and should never delay operative intervention when vascular compromise is present.
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The radial pulse may be present with brachial artery compromise as a result of collateral circulation.
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The absence of a radial pulse in the presence of a warm, wellperfused hand likely represents arterial spasm.
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Medial ecchymosis, a sign of MCL disruption, is typically apparent 3 to 5 days after injury.
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ASSOCIATED INJURIES
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Associated fractures most often involve the radial head and/or coronoid process of the ulna. Shear fractures of the capitellum and/or trochlea are less common.
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Acute neurovascular injuries are uncommon; the ulnar nerve and anterior interosseous branches of the median nerve are most commonly involved.
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The brachial artery may be injured, particularly with an open dislocation.
RADIOGRAPHIC EVALUATION
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Standard anteroposterior and lateral radiographs of the elbow should be obtained.
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Congruence of the ulnohumeral and radiocapitellar joints should be assessed.
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Radiographs should be scrutinized for associated fractures about the elbow.
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Valgus stress views at 30 degrees elbow flexion and full forearm pronation, obtained after initial reduction or at surgery, may help identify an MCL injury.
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Computed tomography (CT) scans may help identify bony fracture fragments not visible on plain radiographs.
CLASSIFICATION
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Simple versus complex (associated with fracture)
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