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° in the balanced condition and 176% (P = .048) of intact at 30°. SCR decreased glenohumeral contact pressure to 110% (185 ± 27 kPa; P = .044) of intact at 0° and to 95% (P = .034) at 30°. Unbalanced ISST contact pressure was 146% (365 ± 23 kPa; P = .009) of intact (250 ± 24 kPa) at 0° and 122% (P = .045) at 60°. SCR decreased contact pressures to 110% (274 ± 21 kPa; P = .039) of intact at 0° and to 89% (P = .003) at 60°. 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°. 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.