Tensile and shear mechanical properties of rotator cuff repair patches

Abstract

Augmentation of rotator cuff tears aims to strengthen the repair and reduce rerupture, yet studies still report high failure rates. This study determines key mechanical properties of rotator cuff repair patches, including establishing values for toughness and measuring the shear properties of repair patches and human rotator cuff tendons. We hypothesized that different repair grafts would (1) have varying material parameters, and (2) not all have mechanical properties similar to human rotator cuff tendons. Eight specimens each from the Restore, GraftJacket, Zimmer Collagen Repair, and SportsMesh repair patches were tested to failure in tension and for suture pullout. We assessed ultimate tensile strength, tensile (Young's) modulus, and failure strain. This study also established toughness values and shear data. Storage modulus was calculated using dynamic shear analysis for the patches and 18 samples of normal rotator cuff tendon. We report significant variability in important mechanical properties of repair patches, with the mechanical parameters of the patches diverting variously-and often significantly-from values for human rotator cuff tendon. The repair grafts tested all displayed significant variation in their mechanical properties and had at least some reduced parameters compared with human rotator cuff tendons. This study offers experimentally derived information of value to surgeons when selecting rotator cuff repair grafts. A better understanding of the mechanical suitability of repair grafts for supporting human rotator cuffs is needed if repair patches are to provide a solution for the clinical problem of failure of rotator cuff repairs.