Effects of capsular plication and rotator interval closure in simulated multidirectional shoulder instability.

BACKGROUND: Arthroscopic treatment of multidirectional shoulder instability with use of capsular plication and rotator interval closure has been shown to be effective in several clinical studies; however, the biomechanical effects of these procedures have not been elucidated. The purpose of this study was to assess biomechanically the effect of arthroscopic capsular plication combined with rotator interval closure on rotational range of motion, humeral head position throughout rotation, and glenohumeral translation.

METHODS: Seven cadaveric shoulders were stretched to 10% beyond the maximum range of motion in 60 degrees and 0 degrees of glenohumeral abduction. Testing was performed for the intact and stretched conditions and following three sequential capsular repairs: anterior plication, posterior plication, and rotator interval closure. Rotational range of motion, humeral head position throughout the range of motion, and glenohumeral translations were measured in both positions.

RESULTS: Stretching increased the total rotational range of motion in 60 degrees and 0 degrees of abduction. After anterior plication alone, total rotation decreased significantly (p < 0.05) in both positions and was restored to the intact state. Total translation with a 20-N load increased significantly in the 60 degrees of abduction position after stretching (p = 0.03). Anterior-posterior translation decreased significantly compared with the stretched state only after all components of the repair were completed in 60 degrees of abduction (p = 0.0003 with a 15-N load and p = 0.0001 with a 20-N load). This decrease was also found to be significantly less than the intact condition (p = 0.008 with a 15-N load and p = 0.001 with a 20-N load). A similar trend in results was found with superior-inferior translations in the 0 degrees of abduction position.

CONCLUSIONS: Capsular plication alone reduces range of motion to the intact state. Reductions in translation, however, may require the addition of rotator interval closure. Changes in translation and rotation after repair are dependent on arm position. In some positions, the addition of rotator interval closure may also result in overtightening.