OVERCORRECTED GLENOID IMPLANTS TO AVOID RECURRENT SUBLUXATION AFTER TOTAL SHOULDER ARTHROPLASTY: A PATIENT-SPECIFIC FINITE ELEMENT ANALYSIS

Hypothesis: Total shoulder arthroplasty is an efficient treatment to osteoarthritis but has a relatively high failure rate. One of the main causes were found to be glenoid loosening associated with off-center loadings. An implant with an overcorrected design at the glenoid contact side is proposed to prevent excessive humeral head sliding and thus reduce the risk of postoperative recurrence of subluxation. It is hypnotized that this mechanism leads to increased strain and stresses at the peri-implant area associated with implant failure. Methods: The study analyzed the right and the left shoulder of one patient. 3-D scapula model was obtained by segmentation of cortical and trabecular bone from patient’s computer tomography (CT) images. The morphology of the osteoarthritic glenoid was analyzed and subsequently a virtual arthroplasty was performed. In a first try implants were chosen and positioned based on manufacturer and surgeon references but for the simulations the implants were chosen and placed according to pre-operative planning and post-operative CTimages. To examine effect of subluxation on different implant designs, particular loading cases were derived and applied in the finite element model. Results: Simulating posterior subluxation, the overcorrected design was able to reduce posterior humeral head subluxation and excessive stress incidence on the peri-implant area compared to the standard design. For overcorrected implant designs, cement volume of highest maximal principal stresses that exceeded the fatigue limit was reduced from 0.22% to 0.06% when augmented implants were modeled and even from 0.50% to 0.01% when the implants with the standard backside were modeled. Conclusion: The study demonstrated the promising potential of the new implant design regarding the reduction of post-operative subluxation reoccurrence. Based on the obtained findings, the hypothesis about increased strains or stresses on the cement mantle could be refuted.