Supraspinatus tendon repair using anchors: a biomechanical evaluation in the rabbit

Background: Arthroscopic rotator cuff repairs are mostly secured with suture anchors and often supplemented by footprint decortication. The objectives of this study were to characterize the strength of bone-tendon healing following anchor repair and assess the effect of channeling the supraspinatus (SSP) humeral footprint 1 week ahead of reattachment surgery. Methods: One hundred twelve rabbits underwent unilateral detachment of one SSP tendon and were randomly assigned to two groups: channeling the footprint at time of detachment and no channeling. One week later, reattachment was performed using an anchor. The repaired and contralateral shoulders were harvested at 0, 1, 2, or 4 weeks after repair and mechanically tested to failure. Outcome measures included load at failure, stiffness, and site of failure. Results: Anchor fixation had a mean load at failure of 81 +/- 32 N and a stiffness of 27 +/- 9 N/mm immediately after repair compared to 166 +/- 47 N and 66 +/- 13 N/mm in the contralateral (both p < 0.05). Mechanical recovery of the reattached SSP tendon was achieved after 4 weeks (221 +/- 73 N, 206 +/- 59 N, and 198 +/- 49 N in the channeling, no channeling, and contralateral groups, respectively, p > 0.05). The dominant site of failure shifted from the footprint at 0/1 week to bone avulsion/mid-substance tear at 4 weeks (p < 0.05). There were no differences in outcomes between the channeling and no channeling groups. Conclusions: This study is the first of its kind to provide quantitative data on the mechanical properties of the enthesis following anchor repair in a rabbit model. Anchor repair led to rapid and complete restoration of SSP mechanical properties. Further evidence is needed before recommending channeling ahead of repair surgery.