Biomechanical Effect of Thickness and Tension of Fascia Lata Graft on Glenohumeral Stability for Superior Capsule Reconstruction in Irreparable Supraspinatus Tears

Abstract

To investigate the effects of graft length and thickness on shoulder biomechanics after superior capsule reconstruction. Subacromial peak contact pressure and glenohumeral superior translation were measured at 0°, 30°, and 60° of glenohumeral abduction in 8 fresh-frozen cadaveric shoulders under 5 conditions: (1) intact shoulder; (2) irreparable supraspinatus tendon tear, (3) superior capsule reconstruction with a fascia lata allograft 4-mm thick and 15 mm longer than the distance from the superior glenoid to the lateral edge of the greater tuberosity, as determined during placement at 30° of glenohumeral abduction; (4) superior capsule reconstruction with a fascia lata allograft 8-mm thick and with the same 15 mm relative length determined at 10° of glenohumeral abduction, and (5) superior capsule reconstruction with a fascia lata allograft 8-mm thick and with the 15-mm relative length determined at 30° of glenohumeral abduction. To investigate the effect of graft thickness, we compared the data from conditions 1, 2, 3, and 5. To assess the effect of graft length, we compared conditions 1, 2, 4, and5. With superior capsule reconstruction using a 4-mm graft, subacromial peak contact pressure (but not superior translation) was significantly lower than with irreparable supraspinatus tears (at 0° abduction: 259% decrease; P= .0002; at 30° abduction: 113% decrease; P= .01). The superior capsule reconstruction using an 8-mm graft significantly decreased both subacromial peak contact pressure (at 0° abduction: 246% decrease, P= .0002; at 30° abduction: 158% decrease; P= .0008; at 60° abduction: 57% decrease; P= .04) and superior translation (at 0° abduction: 135% decrease; P= .02; at 30° abduction; 130% decrease; P= .004). Graft length with placement at 10° glenohumeral abduction was 5 mm greater than that at 30° abduction. The 8-mm superior capsule reconstruction performed at 10° or 30° of glenohumeral abduction significantly decreased subacromial peak contact pressure (placement at 10° and 30°: 0° abduction, P= .0002 and .0002, respectively; 30° abduction, P= .0004 and .0005, respectively; 60° abduction, P= .04 and .04, respectively) and superior translation (placement at 10° and 30°; 0° abduction, P=.04 and .02, respectively; 30° abduction, P= .02 and .004, respectively) compared with irreparable supraspinatus tears. Superior capsule reconstruction normalized the superior stability of the shoulder joint when the graft was attached at 10° or 30° of glenohumeral abduction. An 8-mm-thick graft of fascia lata had greater stability than did a 4-mm-thick graft. Grafts 8-mm thick and attached at 15° to 45° of shoulder abduction (equal to 10° to 30° of glenohumeral abduction) biomechanically restore shoulder stability during superior capsule reconstruction using fascia lata.