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. 2023 Jan 25;11(1):23259671221119542.
doi: 10.1177/23259671221119542. eCollection 2023 Jan.

Deltotrapezial Stabilization of Acromioclavicular Joint Rotational Stability: A Biomechanical Evaluation

Benjamin C Hawthorne  1 , Michael R Mancini  1 , Ian J Wellington  1 , Michael B DiCosmo  1 , Matthew E Shuman  1 , Maxwell T Trudeau  1 , Caitlin G Dorsey  1 , Elifho Obopilwe  1 , Mark P Cote  1 , Augustus D Mazzocca  2
Affiliations

Deltotrapezial Stabilization of Acromioclavicular Joint Rotational Stability: A Biomechanical Evaluation

Benjamin C Hawthorne et al. Orthop J Sports Med. .

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.

Keywords: AC joint; acromioclavicular joint; anatomy; biomechanics; general; shoulder.

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Conflict of interest statement

One or more of the authors has declared the following potential conflict of interest or source of funding: The study was funded internally by the University of Connecticut Department of Orthopaedic Surgery. Implants for the study were donated by Arthrex; the company had no influence on the study design, data collection, or interpretation of the results or the final manuscript. A.D.M. has received consulting fees from Arthrex and Astellas Pharma, speaking fees from 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.

Figures

Figure 1.
Figure 1.
Experimental design of testing and dissection sequence.
Figure 2.
Figure 2.
Biomechanical testing setup. (A) Custom-made fixture allowed for rotational testing of the clavicle with the scapula secured to the servohydraulic testing system. (B) The pulley system allowed for loading of the deltoid and trapezial muscles.
Figure 3.
Figure 3.
Images representing the 4 conditions under which the specimens were tested: (A) intact, (B) “trapezius cut first” defect, (C) “deltoid cut first” defect, (D) combined deltotrapezial defect. Images are rotated 90° for anatomic orientation. AC, acromioclavicular.
Figure 4.
Figure 4.
Anatomic deltotrapezial repair. (A) Illustration of repair demonstrating the PDS suture (purple) running along the defect to reinforce muscular attachment and the medial (blue) and lateral (black) limbs of the suture anchor repair. Black arrows denote anchor insertion site. (B) Completed repair in the MTS machine.
Figure 5.
Figure 5.
Change from native posterior rotational torque. Mean percentage change in torque required for 20° of posterior clavicular rotation in various conditions: intact (native), deltoid defect, trapezial defect, deltotrapezial defect, and after repair. Error bars denote SD. *Statistically significant decrease from intact. ^ Statistically significant increase from deltotrapezial defect. OR, odds ratio.
Figure 6.
Figure 6.
Change from native anterior rotational torque. Mean percentage change in torque required for 20° of anterior clavicular rotation in various conditions: intact (native) condition, deltoid defect, trapezial defect, deltotrapezial defect, and after repair. Error bars denote SD. *Significant decrease compared with intact (P < .05). OR, odds ratio.
See this image and copyright information in PMC

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