The Sonographic Posterolateral Rotatory Stress Test for Elbow Instability: A Cadaveric Validation Study

Background: Although clinical tests can detect posterolateral rotatory instability (PLRI) of the elbow, the ability of ultrasound to evaluate PLRI has not been assessed. Objective: To determine whether increasing stages of posterolateral rotatory subluxation of the elbow could be assessed accurately with a sonographic posterolateral rotatory stress test. Design: Cadaveric study. Setting: Laboratory. Patients: Ten, unpaired, cadaveric upper limbs. Methods: Posterolateral ulnohumeral distance was measured by ultrasound at rest and during manual sonographic posterolateral rotatory stress testing at 4 stages of increasing instability: (1) intact elbow, (2) extensor carpi radialis brevis (ECRB) release, (3) ECRB release + lateral collateral ligament complex (LCLC) release to produce a positive posterolateral drawer test, and (4) ECRB release + LCLC and capsule release to produce a positive lateral pivot-shift test. Mean values for sonographic resting ulnohumeral distance, stressed ulnohumeral distance, and laxity were calculated for each stage and compared between stages. Main Outcome Measures: Posterolateral ulnohumeral laxity. Results: Mean ulnohumeral laxities were 1, 3, 6, and 10 mm (P < .001) for stages 1-4, respectively. Pairwise comparison of mean laxity between the intact elbow (Stage 1) and each pathologic state (Stages 2.4) demonstrated differences of 2 mm (Stage 1 versus 2); 5 mm (Stage 1 versus 3); and 9 mm (Stage 1 versus 4) (P < .001). The minimal difference in ulnohumeral laxity noted between the intact elbow and an elbow with a clinically positive posterolateral rotatory drawer test (Stage 3) was 4 mm. Conclusions: The sonographic posterolateral rotatory stress test detected increasing posterolateral ulnohumeral laxity as a function of increasing clinical PLRI. This test may be used as an adjunct to history, examination, and static imaging to assess ulnohumeral laxity in patients with lateral elbow pain syndromes. Within the limits of this investigation, sonographic posterolateral ulnohumeral laxity of >4 mm should raise suspicion of underlying instability.