Long-Term Wear Analysis of Retrieved Medially Pivoting TKA Inserts

Abstract

Traditional measurement techniques used to evaluate wear estimates of retrievals are qualitative in nature or lack resolution leading to over- or underestimation of wear volume. The purpose of the study was to utilize new imaging techniques such as three-dimensional laser scanning to measure the tibial insert retrieval wear. In vitro simulator data show that the ultra-high molecular weight polyethylene in the Medial-Pivot knee has a low wear rate but little data exist to describe the in vivo long-term wear properties of the Medial-Pivot knee. Three-dimensional laser scanning—a nondestructive, high-resolution imaging technique—was used to create articulating surface geometry of the Medial-Pivot tibial inserts retrieved from patients and surface deviation maps to accurately quantify wear. Wear analysis was performed on 20 retrieved inserts. in vivo service life ranged from 0.1 to 11.9 years (average: 4.8 years; standard deviation: 3.7 years). Surface scans of the entire part were obtained using an ExaScan laser scanner (accuracy: 40 µm). Dimensional analysis was performed using Geomagic Qualify®, which compared the scanned data to the computer-aided design model. The dimensional changes between the scanned and computer-aided design models were considered as wear. The wear rate of each retrieved tibial insert was calculated by dividing the maximum wear by the length of the implantation. The average linear wear rates were 0.052 mm/year and 0.030 mm/year for the medial and lateral compartments, respectively. The overall wear rate of both compartments combined was 0.081 mm/year and is on the low end of the range of wear rates reported for several manufacturers in the literature (0.02 mm/year to 0.67 mm/year). The findings from the current study indicate that the Medial-Pivot inserts can achieve low long-term wear rates. The technique used in the current study allows for rapid, accurate analysis of wear across the entire surface of the implant.