Dermal allograft superior capsule reconstruction biomechanics and kinematics

Purpose: To investigate the effect of a dermal allograft superior capsule reconstruction (SCR) on kinematics and joint pressure biomechanics immediately after simulated superior irreparable rotator cuff tear. Methods: This controlled laboratory study tested 8 fresh-frozen cadaveric shoulders using a custom test frame. Balanced loading configuration centered the humeral head on the glenoid, and unbalanced load created a force pulling the head toward the acromion. Experimental conditions included the intact rotator cuff, irreparable supraspinatus tear (ISST), and dermal allograft SCR. A digital sensor measured glenohumeral and subacromial contact pressure maps, and a microscribe measured the acromion-humeral distance. Results: Glenohumeral contact pressure of ISST was 175% (295 +/- 44 kPa; P = .018) of the intact rotator cuff value (169 +/- 10 kPa) at 0 degrees in the balanced condition and 176% (P = .048) of intact at 30 degrees. SCR decreased glenohumeral contact pressure to 110% (185 +/- 27 kPa; P = .044) of intact at 0 degrees and to 95% (P = .034) at 30 degrees. Unbalanced ISST contact pressure was 146% (365 +/- 23 kPa; P = .009) of intact (250 +/- 24 kPa) at 0 degrees and 122% (P = .045) at 60 degrees. SCR decreased contact pressures to 110% (274 +/- 21 kPa; P = .039) of intact at 0 degrees and to 89% (P = .003) at 60 degrees. ISST increased superior migration of the humeral head, decreasing the acromion-humeral distance by 3.0 +/- 0.6 mm (P = .006) in the unbalanced condition at 0 degrees. SCR increased the acromion-humeral distance to a value similar to that of the intact cuff (P = .003). SCR significantly lowered subacromial pressures in the unbalanced condition. Conclusions: In an irreparable supraspinatus tear model, the dermal allograft SCR showed competency in stabilizing the glenohumeral joint, decreasing glenohumeral and subacromial contact pressures, and increasing the acromion-humeral distance. Level of Evidence: Basic Science Study; Biomechanics (c) 2021 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.