Anterior and posterior musculotendinous anatomy of the supraspinatus

The objective of this study was to quantitatively describe the supraspinatu s musculotendinous architecture. After supraspinatus muscles were harvested from 25 embalmed shoulders, each muscle was divided into an anterior and p osterior muscle belly on the basis of muscle fiber insertion. Pennation ang les and musculotendinous dimensions were measured, and the physiologic cros s-sectional area was calculated for each muscle belly. The physiologic cros s-sectional areas of the anterior and posterior bellies were calculated to be 140 +/- 43 mm(2) and 62 +/- 25 mm(2) respectively, whereas their tendon cross-sectional areas were 26.4 +/- 1 1.3 mm(2) and 31.2 +/- 10. 1 mm(2) re spectively. The average anterior-to-posterior ratios for the muscle physiol ogic cross-sectional area and the tendon cross-sectional area were 245 +/- 0.82 and 0.87 +/- 030 respectively Thus, a larger anterior muscle pulls thr ough a smaller tendon area. These data suggest that physiologically, anteri or tendon stress is significantly greater than posterior tendon stress and that rotator cuff tendon repairs should incorporate the anterior tendon whe never possible, inasmuch as it functions as the primary contractile unit.