<i>In vivo</i> wear measurement in a modern total knee arthroplasty with model-based radiostereometric analysis.

Abstract

A retrospective study was conducted to measure short-term <i>in vivo</i> linear and volumetric wear of polyethylene (PE) inserts in 101 total knee arthroplasty (TKA) patients using model-based radiostereometric analysis (MBRSA). Nonweightbearing supine RSA exams were performed postoperatively and at six, 12, and 24 months. Weightbearing standing RSA exams were performed on select patients at 12 and 24 months. Wear was measured both linearly (joint space) and volumetrically (digital model overlap) at each available follow-up. Precision of both methods was assessed by comparing double RSA exams. Patient age, sex, body mass index, and Oxford Knee Scores were analyzed for any association with PE wear. Linear wear occurred at 0.015 mm/year (supine) and 0.220 mm/year (standing). Volumetric wear occurred at 10.3 mm³/year (supine) and 39.3 mm³/year (standing). Wear occurred primarily on the medial side of the joint. Weightbearing imaging greatly improved the reliability of measurement. Clinical precision of volumetric wear was 34 mm³. No significant associations were found between patient demographics or function scores and measured wear. <i>In vivo</i> volumetric wear of TKAs can be assessed at short-term follow-up using MBRSA. Cite this article: <i>Bone Joint J</i> 2019;101-B:1348-1355.