Neer Award 2017: wear rates of 32-mm and 40-mm glenospheres in a reverse total shoulder arthroplasty wear simulation model

• Published in: Journal of shoulder and elbow surgery Vol. 26; no. 11; pp. 2029 - 2037
• Main Authors: Haggart, John, Newton, Michael D., Hartner, Samantha, Ho, Anthony, Baker, Kevin C., Kurdziel, Michael D., Wiater, J. Michael
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.11.2017
• Subjects: Arthroplasty, Replacement, Shoulder; bearing surface roughness; Computer Simulation; Equipment Failure Analysis; glenosphere size; Humans; Imaging, Three-Dimensional; in vitro wear simulation; Materials Testing; micro-CT analysis; Polyethylene; Prosthesis Design; Prosthesis Failure; Reverse total shoulder arthroplasty; Shoulder Prosthesis; wear particle morphology; X-Ray Microtomography; micro-CT analysis; Tribology Study; Basic Science; in vitro wear simulation; wear particle morphology; glenosphere size; bearing surface roughness; Reverse total shoulder arthroplasty
• ISSN: 1058-2746; 1532-6500
• DOI: 10.1016/j.jse.2017.06.036

Larger glenosphere diameters have been used recently to increase prosthesis stability and impingement-free range of motion in reverse total shoulder arthroplasty. The goal of this study was to evaluate the rate of polyethylene wear for 32-mm and 40-mm glenospheres. Glenospheres (32 mm and 40 mm, n = 6/group) and conventional polyethylene humeral liners underwent a 5–million cycle (MC) wear simulation protocol. Abduction-adduction and flexion-extension motion profiles were alternated every 250,000 cycles. At each interval, mass loss was determined and converted to volume loss and wear rate. At 0, 2.5 MC, and 5 MC, liners were imaged using micro–computed tomography to determine surface deviation. White light interferometry was performed on liners and glenospheres at 0 and 5 MC to quantify surface roughness. Wear particle morphology was characterized by environmental scanning electron microscopy. Total volume loss was significantly higher in 40-mm liners from 1.5 MC onward (P < .05). Overall, volumetric wear rate was significantly higher in 40-mm liners compared with 32-mm glenospheres (81.7 ± 23.9 mm3/MC vs. 68.0 ± 18.9 mm3/MC; P < .001). However, micro–computed tomography surface deviation results demonstrated increased linear penetration on 32-mm glenospheres compared with 40-mm glenospheres (0.36 ± 0.03 µm vs. 0.28 ± 0.01 µm; P = .002). Surface roughness measurements showed no difference for liners; however, increased roughness was noted for 40-mm glenospheres at 5 MC compared with 32 mm (P < .05). Larger glenospheres underwent significantly greater polyethylene volume loss and volumetric wear rates, whereas smaller glenospheres underwent greater polyethylene surface deviations. The enhanced stability provided by larger glenospheres must be weighed against the potential for increased polyethylene wear.