Biomechanical comparison of a novel circular glenoid with peripheral ring fixation to a standard anchor pegged glenoid in total shoulder arthroplasty

Abstract

BackgroundCurrent standard total shoulder pegged glenoid component designs have a high rate of loosening, which accounts for the most common long-term reason for surgical failure. Glenoid design, method of fixation, and implantation version all play a role in component stability. This study aimed to evaluate the biomechanical stability of a novel circular glenoid with peripheral ring fixation and compare to a standard anchor pegged glenoid both directly and to historical biomechanical data. Additionally, we compared the estimated bone removal for the glenoid design types. MethodsBiomechanical testing was performed to assess the circular glenoid with peripheral ring fixation with regards to stability and resistance to “rocking horse” effect, torsional loosening, resistance to torque dissociation, and axial pullout strength. This was compared directly (pullout strength) and to historical (“rocking horse”) biomechanical data obtained for a standard anchor pegged glenoid. A 3D Computer-Aided Design model of five different scapula sizes and shapes was also utilized to estimate volume bone removed when using implant specific prep instrumentation for each glenoid system. ResultsTensile displacement of the worst-case ring fixation component (size medium) after dynamic rocking was 0.060 mm requiring an average peak torque of 6.21N-m to dissociate the glenoid. The ring fixation component demonstrated a mean pullout strength of 1367 N compared with 645 N for the standard anchor pegged glenoid component. The ring fixation component revealed no loosening when placed under torsional stress. The peripheral ring fixation glenoid preparation on average removed 45% less bone than a standard anchor pegged glenoid. ConclusionThe circular glenoid with peripheral ring fixation demonstrated superior maximum pullout strength and more bone preservation with glenoid preparation when compared to the standard pear-shaped, pegged glenoid components. Compared to published standard pegged glenoid component controls, the glenoid with peripheral ring fixation demonstrated diminished “rocking horse” displacement. Despite the circular anchor ring design, there was no evidence of loosening under torsional stress. Initial biomechanical data is overall promising for this novel glenoid design.