Improved restoration of biomechanical factors using a narrow-box shape reconstruction compared to a wide one in superior capsular reconstruction for irreparable supraspinatus tendon tears. A biomechanical study using a static shoulder simulator.

Purpose: To biomechanically compare superior glenohumeral translation, subacromial contact pressures and area in a box-shape reconstruction using the long head of biceps tendon (LHBT) in an irreparable supraspinatus tendon tear model.

Methods: Seven cadaveric shoulders (mean age 61 years; range 32-84 years; SD 22.3) were tested with a custom testing rig used to evaluate superior translation, subacromial contact pressures and areas at 0°, 30° and 60° of glenohumeral abduction. Conditions tested included the native state, a complete tear of the supraspinatus tendon, a wide box-shaped, double-bundle LHBT superior capsular reconstruction (wide BS-SCR), and a narrow box-shaped, double-bundle LHBT superior capsular reconstruction (narrow BS-SCR).

Results: Compared to the wide box-shape SCR, the narrow box-shape SCR had statistically significant lower median contact pressure at 30° and 60°. The subacromial contact area showed a statistically significant difference at 0° (p=0.001) and 30° (p=0.004) for the narrow compared to wide box-shape SCR. At an abduction angle of 0°, the narrow SCR could restore superior translation statistically significant better compared to the wide construct. For all angles, the wide and narrow box-shaped SCR increased the median subacromial distance statistically significantly. The contact areas in 30° and 60° of abduction were higher for all scenarios, both peaking in the intact state in 30° with approximately 600 mm².

Conclusions: In comparison to a wide box-shape, a narrow box-shape SCR using the LHBT has biomechanical advantages in regard of subacromial contact pressures, the subacromial contact areas as well as the acromiohumeral distance. The width of the reconstruction therefore has direct influence in the success of the technique.