Histological incorporation of acellular dermal matrix in the failed superior capsule reconstruction of the shoulder

Background Superior capsule reconstruction addresses massive rotator cuff tears using allografts and aims to restore the natural superior constraint of the shoulder and therefore shoulder biomechanics and function. There is no evidence relating to the histological incorporation of these grafts. Methods 27 superior capsule reconstructions were performed between June 2016 and November 2017. Follow-up was with clinical assessment and Magnetic Resonance Imaging, to identify graft failure. Reverse total shoulder replacement was offered for ruptured grafts and the graft was sent for histological analysis along with the footprint of graft attachment where possible. Results Five patients (18.5%) had evidence of graft failure, three of whom (11.1%) underwent revision procedures. Of the five ruptures, four failed at the glenoid insertion, and one was an intra-substance tear. Histological analysis showed extensive fibroblastic infiltration. The intra-substance tear showed some vascularity at the medial and lateral ends, and one of the glenoid pull-outs demonstrated micro-calcification and osteoid formation. There was no evidence of in-growth into the bone. Discussion An inflammatory response to the grafts was seen, with neo-vascularisation, and micro-calcification observed. These findings are from ruptured grafts, so may not represent the characteristics of those which have not ruptured. Further evidence from explanted intact grafts could be gained to improve our understanding of its incorporation.