Background: The contributions of the scapulothoracic articulation and spine when measuring shoulder range of motion have been well described; however, the effect of elbow valgus laxity has not.
Hypothesis: Increased elbow valgus laxity affects the assessment of shoulder external rotation measured during physical examination at 90° of elbow flexion.
Study Design: Controlled laboratory study.
Methods: Seven cadaveric upper extremities were tested with an elbow valgus laxity–testing device. Shoulder external rotation was assessed with 2.8 N · m of external torque by measuring a change in the angle of the forearm axis at 90° of elbow flexion. Elbow valgus laxity was measured in degrees of valgus angulation with 1.5 N · m of valgus torque with the humerus fixed. Shoulder external rotation and elbow valgus laxity were recorded at each of the following conditions: (1) intact, (2) after splitting the pronator muscles and venting the capsule, (3) after cutting the posterior band of the anterior oblique ligament of the ulnar collateral ligament, and (4) after cutting the anterior oblique ligament completely.
Results: After the posterior band of the anterior oblique ligament of the ulnar collateral ligament was cut, apparent shoulder external rotation and elbow valgus laxity were increased by 4.1° ± 1.7° (P < .01) and 3.1° ± 1.3° (P < .001), respectively, when compared with the intact condition. Complete cutting of the anterior oblique ligament resulted in an apparent increased shoulder external rotation and an increased elbow valgus laxity of 11.0° ± 1.1° (P < .001) and 9.1° ± 1.2° (P < .001), respectively, when compared with the intact condition.
Conclusion: Shoulder external rotation as assessed by physical examination, which was defined as the angle of the forearm axis, as well as elbow valgus laxity, was significantly increased after the anterior oblique ligament of the ulnar collateral ligament was cut, although the glenohumeral joint condition was not changed.
Clinical Relevance: Elbow valgus laxity may cause an overestimation of shoulder external rotation on clinical examination of the shoulder.