The 6 O’Clock Anchor Increases Labral Repair Strength in a Biomechanical Shoulder Instability Model

Abstract

Objectives: Despite a growing body of literature regarding optimal repair configurations, little is known about inferior suture anchor placement (6 o’clock position). Here, we determine the biomechanical strength of adding a 6’oclock anchor to a “standard” Bankart repair in a normal glenoid and a 13% anterior bone loss model. Methods: 12 cadaveric shoulders were tested on a six axis industrial robot to measure the peak resistance to translation force with anterior displacement (1 centimeter). The rotator cuff muscles were loaded during testing to simulate physiological conditions. Test conditions included intact shoulder, Bankart lesion, Bankart repair (3, 4, and 5 o’clock anchors), and Bankart repair with a 6 o’clock anchor. A 13% anterior bone defect was then created (based on pretest CT scan) and all conditions were repeated. Repeated measures ANOVA was used to test for significant differences among groups. Results: In the no bone loss group, the addition of a 6 o’clock anchor yielded the highest peak resistance force (52.8 N, SD: 4.5 N) and was significantly stronger than the standard Bankart repair by 15.8% (7.2 N, p = 0.003). With 13% bone loss from the anterior glenoid, both the standard Bankart repair (peak force 49.3 N, SD: 6.1 N, p = 0.02) and repair with the addition of the 6 o’clock anchor (peak force 52.6 N, SD: 6.1 N, p = 0.006) had a significantly higher peak resistance force compared to the bone loss with Bankart lesion group (35.2 N, SD: 5.8 N). While the 6 o’clock anchor did increase the strength of the standard repair by 6.7%, this was not statistically significant (p = 0.9) in the bone loss model. Conclusion: The addition of a 6 o’clock suture anchor to a ”standard” Bankart repair increases to the peak resistance to translation force (no bone loss), although this additional strength is lost with creation of a 13% anterior glenoid bone defect.