Analysis of polyethylene wear of reverse shoulder components: A validated technique and initial clinical results

One of the most prevalent phenomena associated with reverse total shoulder arthroplasty (rTSA) is scapular notching. Current methods examine only the damage to the scapula and no methods are available for quantifying the total wear volume of the polyethylene humeral bearing. Quantifying the polyethylene material loss may provide insight into the mechanism for scapular notching and into the particle dose delivered to the patient. A coordinate measurement machine (CMM) and custom computer algorithms were employed to quantify the volumetric wear of polyethylene humeral bearings. This technique was validated using two never‐implanted polyethylene humeral liners with a controlled amount of wear in clinically relevant locations. The technique was determined to be accurate to within 10% of the known value and within 5 mm³ of the gravimetrically determined values. Following validation, ten retrieved polyethylene humeral liners were analyzed to determine a baseline for future clinical tests. Four of the ten polyethylene humeral liners showed visible and measureable wear volumes ranging from 40 to 90 mm³ total with a maximum wear rate as high as 470 mm³/year in one short duration and significantly damaged humeral liner. This validated technique has the potential to relate patient outcomes such as scapular notching grades to polyethylene release into the body. While the total wear volumes are less than reported in literature for cases of osteolysis in knee and hip patients, dosages are well within the osteolytic thresholds that have been suggested, indicating that osteolysis may be a clinical concern in the shoulder. This work provides the basis for future studies that relate volumetric wear to patient outcomes.

© 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:980–987, 2017.