An experimental glenoid rim strain analysis for an improved reverse anatomy shoulder implant fixation

Loosening of glenoid components in TSA is a main cause of failure. In reverse anatomy TSA designs used for unstable joints, fixation is particularly demanding. Strains developed around the glenoid rim of biomechanical sawbone scapulae implanted with (a) the original fixed-fulcrum Bayley-Walker glenoid prosthesis in current clinical use, and (b) a revised version with conical cross-section, were compared. The conical shape of the revised design was hypothesized to produce greater strains in the glenoid rim than the original tapered screw design. The 2D strain field at three accessible locations around the rim of each scapula was measured with three-element rosette strain gauges for two types of simulated cancellous bone fill under applied physiologically relevant loads. The average strain energy densities around the rim for the conical design were greater than for the original design by a factor of 1.55-2.25 for all loading conditions. Results indicate that a significantly greater proportion of load was directed toward cortical bone in the conical design, thus promoting cortical bone loading.