Biomechanical Comparison of Open Bankart Repair vs. Conjoint Tendon Transfer in a 10% Anterior Glenoid Bone Loss Shoulder Instability Model.

BACKGROUND: The treatment of shoulder instability in patients with subcritical glenoid bone loss poses a difficult problem for surgeons as new evidence supports a higher failure rate when standard arthroscopic Bankart repair is utilized. The purpose of this study was to compare a conjoint tendon transfer (Soft Tissue Bristow) to an open Bankart repair in a cadaveric instability model of 10% glenoid bone loss.

METHODS: Eight cadaveric shoulders were tested using a custom testing system that allows for six degree-of-freedom positioning of the glenohumeral joint. The rotator cuff muscles were loaded to simulate physiologic muscle conditions. Four conditions were tested: (1) intact (2) Bankart lesion with 10% bone loss, (3) conjoint tendon transfer, and (4) open Bankart repair. Range of motion, glenohumeral kinematics, and anterior-inferior translation at 60° of external rotation with 20, 30 and 40N were measured in the scapular and coronal planes. Glenohumeral joint translational stiffness was calculated as the linear fit of the translational force-displacement curve. Force to anterior-inferior dislocation was also measured in the coronal plane. Repeated measures ANOVA with Bonferroni correction was used for statistical analysis.

RESULTS: Bankart lesion with 10% bone loss increased range of motion in both the scapular (P = 0.001) and coronal planes (P = 0.001). The conjoint tendon transfer had minimal effect on range of motion (vs. Intact P = 0.019, 0.002), but the Bankart repair decreased the range of motion to Intact (P = 0.9, 0.4). There was a significant decrease in glenohumeral joint translational stiffness for the Bankart lesion compared to intact in the coronal plane (P = 0.021). The conjoint tendon transfer significantly increased stiffness in the scapular plane (P = 0.034) and the Bankart repair increased stiffness in the coronal plane (P = 0.037) compared to the Bankart lesion. The conjoint tendon transfer shifted the humeral head posteriorly in 60° and 90° of external rotation in the scapular plane. The Bankart repair shifted the head posteriorly in maximum external rotation in the coronal plane. There was no significant difference in force to dislocation between the Bankart repair (75.8 ± 6.6 N) and the conjoint tendon transfer (66.5 ± 4.4N). (P = 0.151) CONCLUSION: In the setting of subcritical bone loss, both the open Bankart repair and conjoint tendon transfer are biomechanically viable options for the treatment of anterior shoulder instability, further studies are needed to extrapolate this data to the clinical setting.