Effects of Scapular Notching and Bone Remodelling on Long-Term Fixation of the Glenoid Component in Reverse Shoulder Arthroplasty

Abstract

Reverse shoulder arthroplasty (RSA) has been a proposed surgical treatment for severe rotator cuff deficiency associated with arthritis. Favourable clinical results for this type of prosthesis have been reported from short- and mid-term follow-up studies. However, the high revision rate (5% - 33%) at long-term follow up (i.e. greater than 6 years) is a concern. One of the principal factors leading to RSA failure is glenoid component loosening with an incidence of 5% - 38%. Therefore, one objective of this project is to investigate factors leading to long-term glenoid loosening. As various glenosphere positions have been proposed to minimize scapular notching, the other objective is to predict fixation strengths associated with these new surgical techniques. Scapular notching is one of the most frequently reported complications for Delta RSA, due to the high postoperative incidence of 50% to 96%. In this thesis, the study of scapular notching showed negative effects on the inferior screw safety and safety of the bone close to the screw. The study of initial stability showed that scapular notching may not destroy the good environment for bony ingrowth. Strain-induced bone remodelling has been an important factor for the bone loss after hip and knee joint prosthesis implantations. Effects of this factor on the bone loss after Delta RSA implantations were investigated. The results showed that bone resorption was considerable in the region close to the back of metagelene and the middle stem with a mean reduction of postoperative bone apparent density of approximately 63% at 8-year follow up. Thereby, postoperative bone loss could be caused by three factors: strain-induced bone resorption, scapular notching and osteolysis induced by the polyethylene wear particles. In this study, prosthesis fixations in the case of inferior positioning and downward tilting of the glenosphere were assessed using two parameters: strain-induced bone resorption and initial stability. It was found that inferior positioning may lead to early bone resorption due to the inferior shift of postoperative glenohumeral force. The downward tilting may cause significant increase of bone-prosthesis micromotions and may result in poor initial stabilities of glenoid prosthesis.