Deltotrapezial Stabilization of Acromioclavicular Joint Rotational Stability: A Biomechanical Evaluation

Abstract

Background: Despite advances in surgical management of acromioclavicular (AC) joint reconstruction, many patients fail to maintain sustained anatomic reduction postoperatively. Purpose: To determine the biomechanical support of the deltoid and trapezius on AC joint stability, focusing on the rotational stability provided by the muscles to posterior and anterior clavicular rotation. A novel technique was attempted to repair the deltoid and trapezius anatomically. Study Design: Controlled laboratory study. Methods: Twelve human cadaveric shoulders (mean ± SD age, 60.25 ± 10.25 years) underwent servohydraulic testing. Shoulders were randomly assigned to undergo serial defects to either the deltoid or trapezius surrounding the AC joint capsule, followed by a combined deltotrapezial muscle defect. Deltotrapezial defects were repaired with an all-suture anchor using an anatomic technique. The torque (N·m) required to rotate the clavicle 20° anterior and 20° posterior was recorded for the following conditions: intact (native), deltoid defect, trapezius defect, combined deltotrapezial defect, and repair. Results: When compared with the native condition, the deltoid defect decreased the torque required to rotate the clavicle 20° posteriorly by 7.1% (P =.206) and 20° anteriorly by 6.1% (P =.002); the trapezial defect decreased the amount of rotational torque posteriorly by 5.3% (P =.079) and anteriorly by 4.9% (P =.032); and the combined deltotrapezial defect decreased the amount of rotational torque posteriorly by 9.9% (P =.002) and anteriorly by 9.4% (P.999). The rotational torque of the repair was significantly lower than the native joint in the posterior (P =.017) and anterior (P