Biomechanical effectiveness of lower trapezius tendon transfer with intercalary tendon-bone graft vs. the modified l'Episcopo procedure in reverse total shoulder arthroplasty with proximal humeral bone loss.

Abstract

In reverse total shoulder arthroplasty (rTSA), proximal humeral bone loss (PHBL) is associated with higher complication rates and inferior functional results, particularly loss of active external rotation (ER). Traditionally, adjunct tendon transfers such as the latissimus dorsi transfer or the modified l'Episcopo procedure have been employed to address this. Recently, in native shoulders, lower trapezius transfer (LTT) has gained popularity as an alternative method to restore ER. To date, almost no literature exists on its use in rTSA. The purpose of this study was to evaluate the biomechanical effectiveness of a novel, modified lower trapezius transfer with tendon-bone allograft (LTT+) that aims to reconstruct the greater tuberosity in situations of PHBL and to compare it with the modified l'Episcopo procedure. It was the hypothesis of this study that LTT+ would provide comparatively higher ER and lower adduction (ADD) moments. Ten right, cadaveric upper limbs were prepared by resecting the proximal humerus, creating moderate PHBL (4 cm). rTSA was performed, and both an LTT+ and an l'Episcopo tendon transfer were added. The specimens were mounted on a custom-built testing apparatus, and an optical motion analysis system was employed to record joint kinematics and tendon excursions. During passive rotational and abduction-ADD motion cycles, the ER and ADD moment arms were computed using the tendon-excursion method. Both LTT+ and l'Episcopo are biomechanically effective in generating shoulder ER in rTSA with PHBL. LTT+ moment arms were higher; significance being reached after a minimum of 45° to 55° of ER had been achieved, depending on the angle of abduction. For pooled internal rotation (-20° to 0° rotation), low (0° to 45° rotation), and high ER (45° to 70° rotation), the mean differences of the ER moment arms were significant in all abduction positions (P < .0001 for all 3 groups). The ADD moment arms of LTT+ were significantly lower than l'Episcopo's (P < .0001), measured in neutral rotation in the scapular plant between 40° and 70° abduction. The differences were most relevant in lower degrees of abduction. Biomechanically, both LTT+ and the modified l'Episcopo procedure demonstrated effective shoulder ER capacity. LTT+ provided significantly higher ER moment arms in high degrees of ER, and, additionally, lower ADD moment arms, thereby potentially avoiding interference with the deltoid during abduction and elevation. These effects may strongly depend on the transfers' insertion site and technique.