Contribution of micro‐motion to backside wear in a fixed bearing total knee arthroplasty

Abstract

This study seeks to identify important factors related to backside wear of tibial inserts in vivo and determine an appropriate wear model for backside wear. An IRB approved database was queried for tibial inserts of a single design from one manufacturer that exhibited evidence of rotatory motion on the backside of the polyethylene. These devices were measured for volumetric wear using a previously established protocol. Features including the change in locking lip width and measurement of micro-motion marks were used to describe the motion pattern. Volumetric wear and implant characteristics were compared using linear regressions by modeling wear theories suggested by Archard and Wang to determine the most appropriate model for backside wear. The Wang model showed that duration, adjusted sliding distance, and cross-shear index accounted for approximately 58% of the volumetric wear variation while adjusted sliding distance and duration in vivo accounted for approximately 35% of the volumetric wear variation in the Archard model. Patient weight (p = 0.750), patient BMI (p = 0.680), and backside area (p = 0.784) of the tibial insert were all found to be non-significant in the Wang model. Similarly, patient weight (p = 0.233), patient BMI (p = 0.162), and backside area (p = 0.796) were found to be non-significant in the Archard model. Multidirectional micro-motion appears to contribute significantly to the wear of these components, supporting the Wang theory of cross-shear for polyethylene wear. Cross-shear of polymers on an unpolished titanium tray can lead to an increase in wear debris in the body. Care should be taken when designing locking mechanisms and tray designs. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1933-1940, 2016.

Peripheral snap-fit locking mechanisms and smooth surface finish of tibial trays reduce backside wear in fixed-bearing total knee arthroplasty

“…Using mathematical models of PE wear and data from retrievals, Levine et al. (2016) demonstrated that multidirectional micromotions (which result in arcuate patterns similar to those observed in NexGen knees) play a critical role in backside wear. Our SEM findings—which suggested differences in the extent of micromotion between designs—were confirmed by Bhimji et al.…”

“…2012, Levine et al. 2016). Measurement using micro CT is very precise, but it requires complex equipment, custom software, and time-consuming data processing—and has therefore been used in studies involving a much smaller number of samples than in our material (Crowninshield et al.…”

“…This may seem counter-intuitive, but the lack of any role of BMI and patient weight in backside wear was confirmed in a recent study by Levine et al. (2016) based on mathematical models of polyethylene wear and on data from retrievals. Another factor affecting backside wear is the sterilization method used and oxidative degeneration of polyethylene (Muratoglu et al.…”

Have the Causes of Revision for Total and Unicompartmental Knee Arthroplasties Changed During the Past Two Decades?

“…Paxton et al [56] found a similar risk of revision for highly crosslinked polyethylene compared with conventional polyethylene. Highly crosslinked polyethylene is rarely used in Norway in knee arthroplasty (8% in 2013-2015) [69], indicating improvements in conventional polyethylene and polishing, sterilization, and locking mechanisms [37,39,68]. The risk of revision resulting from malalignment was unchanged for TKA and UKA.…”

Effects of interference assembly of a tibial insert on the tibiofemoral contact mechanics in total knee replacement

“…Although the interference fit of fixed-bearing TKR with locking mechanism was included in functional knee simulator testing of the tibial insert, 10,11 it is rare to investigate the effect of interference fit on articular and backside wear rates of the tibial insert. Compared with retrieval studies and wear testing, finite element analysis (FEA) is an attractive alternative for parametric studying the influence of interference fit between the tibial insert and the tibial tray without expensive experimental cost.…”