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 < .001). Anatomic deltotrapezial repair increased posterior rotational torque by 5.3% posteriorly as compared with the combined deltotrapezial defect ( P = .001) but failed to increase anterior rotational torque ( P > .999). The rotational torque of the repair was significantly lower than the native joint in the posterior ( P = .017) and anterior ( P < .001) directions. Conclusion: This study demonstrated that the deltoid and trapezius play a role in clavicular rotational stabilization. The proposed anatomic repair improved posterior rotational stability but did not improve anterior rotational stability as compared with the combined deltotrapezial defect; however, neither was restored to native stability. Clinical Relevance: Traumatic or iatrogenic damage to the deltotrapezial fascia and the inability to restore anatomic deltotrapezial attachments to the acromioclavicular joint may contribute to rotational instability. Limiting damage and improving the repair of these muscles should be a consideration during AC reconstruction.

Current Concepts in Management of Acromioclavicular Joint Injury

“…The Self Assessment Numeric Evaluation (SANE) score was also collected post-operatively. Studies of acromioclavicular joint reconstruction have previously used mean clinically important difference (MCID), substantial clinical benefit (SCB), and patient acceptable symptomatic states (PASS) as defined for rotator cuff tears of 11, 17.5, and ASES of 86.7 for PASS [ 79 , 80 ]. A 2-tailed t-test was performed to assess for significance of improvement.…”

“…The lateral limb is left 2 cm longer and sutured to the posterior acromial tissue to recreate the AC joint capsule [ 78 ]. The deltoid fascia is then brought over the top and secured with an anchor anteriorly [ 79 ]. A retrospective review of prospectively collected data on patients undergoing ACCRs performed by the senior author was conducted.…”