Glenohumeral translations are increased after a type II superior labrum anterior-posterior lesion: a cadaveric study of severity of passive stabilizer injury

Abstract

The effects of simulated type II superior labrum anterior-posterior (SLAP) lesions were studied to determine whether the severity of the lesion affected glenohumeral joint translations. A robotic/universal force-moment sensor testing system was used to simulate load-and-shift tests by applying an anterior or posterior load of 50 N to each shoulder. The apprehension test for anterior instability was simulated by applying an anterior load of 50 N with an external rotation torque of 3 Nm at 30° and 60° of abduction. This loading protocol was repeated after creating two type II SLAP lesions of different severity. In the first the superior labrum and the biceps anchor were elevated subperiosteally from the glenoid bone (SLAP-II-1), and in the second the biceps anchor was completely detached (SLAP-II-2). Statistical analysis was performed with a 2-factor repeated-measures analysis of variance followed by multiple contrasts, and the significance level was set at P < .05. At 30° of abduction, anterior translation of the vented joint from anterior loading was 18.5 ± 8.5 mm. It was significantly increased (26.2 ± 6.5 mm, P = .03), after the SLAP-II-2 lesion and compared with the SLAP-II-1 lesion (25.0 ± 6.8 mm, P = .03). Increases in anterior translations at 60° of abduction were not significantly differ in comparison to the two SLAP lesions. Inferior translation also resulted from anterior loading. At 30° of abduction in the vented joint, it was 3.8 ± 4.0 mm and was significantly increased (8.5 ± 5.4 mm, P = .05) after the SLAP-II-2 lesion, no different than that after the SLAP-II-1 lesion (7.8 ± 4.9 mm). No significant increases in anterior translation occurred in response to the combined loading condition between the two SLAP lesions. Glenohumeral translation was increased, regardless of severity, after simulation of type II SLAP lesions. During stabilizing surgical interventions, passive stabilizers that are injured in the type II SLAP lesion should be considered as well as dynamic activity in the tendon of the long head of the biceps brachii.