Abstract 29

COMPARISON OF STRAINS IN UNDERLYING GLENOID WITH METAL BACKED AND ALL POLYETHYLENE IMPLANTS

Pelletier, M H; Langdown, A; Gillies, M; Sonnabend, D H; Walsh, W R

Orthopaedic Research Laboratories, University of New South Wales, Prince of Wales Hospital, Sydney, NSW, Australia

The aim of this study is to examine the strain differences in intact glenoids and following replacement with a metal backed keeled component and a cemented all polyethylene pegged component with the same articular geometry. Three fresh frozen adult upper extremities were cleaned of all soft tissue. A 2mm thick photoelastic coating was bonded to all but the articular surface of the glenoid. Eight strain gauges were attached around the periphery in a plane 12mm proximal to the glenoid surface. Loads were applied to the glenoids using the humerus in four angles of abduction (0°,30°,60°,90°) corresponding to four loading conditions (222N, 538N, 924N, 1204N). Preoperative measurements were taken from each intact glenoid to represent the native state. Each specimen was reconstructed using a metal backed, then PE component. Specimens were retested following each surgical procedure. Perpendicular strain gauges values and the photoelastic measurements were used to calculate the principal strains at each point. Results were normalized by angle/load and differences were identified with ANOVA. The metal backed and all PE implants showed similar trends, shifting strains superiorly. Differences were seen between the intact and implanted states in all four of the superior gauges and the posterioinferior gauge. Differences between the two implanted states were only seen in the anterior gauges. Glenoid arthroplasty indeed alters the strain state compared to the intact case, this is just one factor that can influence outcome. This study is limited in that the complex kinematics of the shoulder cannot be replicated in vitro.

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