A Superolaterally Placed Anchor for Subscapularis “Leading-Edge” Refixation: A Biomechanical Study

Abstract

To compare a conventional single-row (SR) repair technique and 2 double-row (DR) repair techniques to restore and protect the superolateral aspect of the subscapularis (SSC) tendon and ensure SSC leading-edge reconstruction in a cadaveric model. The native footprint was measured in 15 pairs of human cadaveric shoulders (N= 30) with a mean age of 67.2years. According to the Fox-Romeo classification, a 25% defect or 50% defect in a superior-inferior direction was created. Specimens were mounted onto a servohydraulic test system to analyze contact variables at 0° and 20° of abduction with a force-controlled ramped program up to 50N. In addition, each specimen was cyclically loaded (10-100N, 300 cycles). The tears were repaired with 1 of 3 constructs: a 2-anchor medially based conventional SR construct, a 2-anchor-based hybrid DR construct, or a 3-anchor-based DR construct. The outcome variables were ultimate tensile load, displacement, and pressurized footprint coverage. All reconstructions resulted in stable constructs with peak loads exceeding 450N(P= .68). The overall displacement during cyclic loading was between 1.2 and 3.0mm(P= .70). A significant difference was seen when the 2 arm positions of 0° and 20° of abduction were compared, showing a constant reduction of pressurized footprint coverage with the arm abducted (P= .01). Analyzing footprint coverage with respect to the region of interest-the leading edge of the SSC-we observed a significant difference between the SR construct and a construct using a superolaterally placed anchor (25% defect, P= .01; 50% defect, P= .01), whereas no statistical differences were detectable between the hybrid DR construct and the DR construct. The leading edge of the SSC tendon can best be restored by using a superolateral anchor, whereas no statistical difference in load to failure in comparison with an SR construct or with the addition of a third anchor was detectable. The SSC is critical for proper shoulder function. Without an increase in the number of implants, a significantly better footprint reconstruction can be achieved by placing an anchor superior and lateral to the native footprint area close to the entrance of the bicipital groove.