The Role of the Trapezius in Stabilization of the Acromioclavicular Joint: A Biomechanical Evaluation.

Background

Acromioclavicular joint (ACJ) injuries are common, and many are adequately treated nonoperatively. Biomechanical studies have mainly focused on static ligamentous stabilizers. Few studies have quantified ACJ stabilization provided by the trapezius.

Purpose/Hypothesis

To elucidate the stabilization provided by the trapezius to the ACJ during scapular internal and external rotation (protraction and retraction). It was hypothesized that sequential trapezial resection would result in increasing ACJ instability.

Study Design

Controlled laboratory study.

Methods

A biomechanical approach was pursued, with 10 cadaveric shoulders with the trapezius anatomically force loaded to normal. The trapezius was then serially transected over 8 trials, which alternated between clavicular defects (CD) and scapular defects (SD); each sequential defect consisted of 25% of the clavicular or scapular trapezial attachment. After each defect, specimens were tested with angle-controlled scapular internal and external rotation (12°) with rotary torque measurements to evaluate ACJ stability.

Results

The mean resistance in rotary torque for 12° of scapular internal rotation (protraction) with native specimens was 7.0 ± 2.0 N·m. Overall, internal rotation demonstrated a significant decrease in ACJ stability with trapezial injury (

Conclusion

Trapezial injury resulted in increased instability in the setting of scapular internal rotation (protraction) of the ACJ.

Clinical Relevance

These findings validate the inclusion of deltotrapezial fascial injury consideration in the modified Rockwood classification system. Repair of the trapezial insertion on the ACJ may provide improved outcomes in the setting of ACJ reconstruction.

Informations de copyright

© The Author(s) 2022.

Déclaration de conflit d'intérêts

One or more of the authors has declared the following potential conflict of interest or source of funding: A.D.M. has received consulting fees from Arthrex and Astellas Pharma, speaking fees from Arthrex and Kairos Surgical, and honoraria from Arthrosurface. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.