Recurrent Posterolateral Rotatory Instability of the Elbow
Traumatic instability of the elbow, acute or recurrent, usually occurs via a mechanism of displacement referred to as “posterolateral rotatory instability.” Posterolateral rotatory instability of the elbow can be defined as an abnormal kinematic (motion) pattern of the elbow in which the forearm (radius and ulna) subluxate away from the humerus in a three-dimensional coupled motion pattern. This occurs during a unique sequence of forces and moments. These include axial load across the elbow with valgus torque starting from the extended position and then, as the elbow flexes, an external rotation torque (internal rotation torque of the humerus) occurs also. An understanding of elbow instability requires knowledge of the lateral collateral ligament complex anatomy as well as mechanism and kinematics of elbow subluxation and dislocation. The lateral collateral ligament complex is the key structure involved in recurrent elbow instability, and it is virtually always disrupted in elbow dislocations that result from a fall. The ulnar part of the lateral collateral ligament complex (also known as “lateral ulnar collateral ligament”) (Fig. 48–1) is the critical portion of the ligament complex that secures the ulna to the humerus and prevents posterolateral rotatory instability.
Posterolateral rotatory instability.
1. Significant coronoid deficiency (unless corrected at the same time)
2. Severe ligamentous laxity (relative)
Mechanism of injury
Elbow subluxations or dislocations typically occur as a result of falls on the outstretched hand. At contact, the elbow immediately begins flexing. Eccentric loading of the triceps, principally the medial head, produces an external rotation moment at the ulnohumeral joint. Contraction of the adductors and internal rotators of the abducted shoulder internally rotate the humerus against the forearm and hand, which are stabilized by the ground. As a result, a valgus moment is produced in which the mechanical axis is medial to the elbow.
The pathoanatomy can be described as a circle of soft tissue and/or bone disruption progressing from lateral to medial in three stages (Figs. 48–2A,B).
1. Lateral pivot shift apprehension test (posterolateral rotatory apprehension test) (Figs. 48–3A,B)
2. Lateral pivot shift test
3. Posterolateral rotatory drawer test
1. EUA—Lateral pivot shift test and posterolateral rotatory drawer test
2. Lateral stress radiograph
3. Arthroscopic examination
Differential Diagnosis and Concomitant Injuries
1. Most often misdiagnosed as MCL deficiency.
2. Mechanical symptoms may mimic loose body.
3. Other injuries often include radial head and/or coronoid fractures.
1. These tests are difficult to perform in a conscious patient, except the apprehension test.
2. Posterolateral rotatory instability (PLRI) is difficult to diagnose if the radial head is absent.
3. False-negative test results may occur if the MCL is deficient.
4. PLRI may be misdiagnosed as valgus instability at the time of lateral arthrotomy for treatment of radial head fracture.
5. If the degree of instability is severe, apprehension may not be present.
1. Bankart awl from shoulder set
2. Double-stranded #1 PDS suture