In vitro biomechanical analysis of glenoïds before and after implantation of prosthetic components

Biomechanical investigations are yet necessary to better understand the origin of the glenoïd loosening which is the main reason for revision surgery. The aim of this study was to analyse the behaviour of cadaveric glenoïds before and after implantation of glenoïd prostheses. For that, we developed a new experimental protocol allowing measurement of bone strains and implants displacements under various loading cases. Ten pairs of fresh cadaveric scapulae were tested. Two kinds of loads were applied on the intact glenoïd: physiological loads corresponding to a 0–180° abduction and anteflexion movements, and 500 N loads. The glenoïds were then implanted with a keeled or pegged cemented polyethylene implant. The same previous 500 N loads were then applied on the implanted glenoïds. Strains were measured using six strain gages placed on precise points around the peripheral cortex of the glenoïd. Displacements of implants under loading were measured using two CCD cameras. Maximum strains were obtained between 60° and 120° of abduction or anteflexion. They were located at the anterior and antero-superior parts of the glenoïd during abduction and at the posterior and postero-superior parts during anteflexion. Implantation of a prosthetic component generally seemed to increase strains, but tensile strains were decreased at the postero-inferior part with the antero-inferior loading point. Some differences were observed between the implants, but they have to be confirmed by further experiments. The great number of data obtained for intact scapulae could be used for a better understanding of glenoïd behaviour and for validation of finite element models.