Bone and Joint Institute

Wear of humeral polyethylene cups in reverse total shoulder arthroplasty with simulated rim damage from scapular notching

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© 2020 Elsevier Ltd Reverse total shoulder arthroplasty (RTSA) is an effective treatment for several shoulder conditions, however scapular notching is common and results in damage to the polyethylene humeral cup. This study assessed the simulator wear of RTSA implants, with and without the presence of simulated scapular notching rim damage. A shoulder wear simulator applied representative shoulder circumduction with a 900 N peak force to five clinically available RTSA implants. The lubricant was alpha calf fraction with a protein concentration of 30 g/L, sodium hyaluronate at 1.5 g/L, and antimycotic antibiotic at 1%. Simulated scapular notching damage was progressively applied every 0.25 Mc. Wear was assessed gravimetrically and load soak controls allowed for the correction of fluid uptake. A finite element model also permitted the investigation of the effects of the simulated damage on articular contact area and stress. All humeral cups showed signs of articular wear in the inferior aspect. After the simulated rim damage, a secondary wear band formed at the inferior edge of the cup, and the finite element analysis showed a reduction of articular contact area and an increase in maximum contact stress at this location. The average volumetric wear rate of the intended articular surface during testing was 25.30 ± 0.92 mm3/Mc and while the wear rate was reduced slightly by the simulated scapular notching damage, likely a result of the reduced articular contact area, the magnitudes of the changes were small. The articular wear zone moved inferiorly as the damage progressed.

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