Wear Damage in Mobile-bearing TKA is as Severe as That in Fixed-bearing TKA

Abstract

Background Mobile-bearing TKAs reportedly have no clinical superiority over fixed-bearing TKAs, but a potential benefit is improved polyethylene wear behavior. Questions/purposes We asked whether extent of damage and wear patterns would be less severe on retrieved mobile-bearing TKAs than on fixed-bearing TKAs and if correlations with patient demographics could explain differences in extent or locations of damage. Methods We performed damage grading and mapping of 48 mobile-bearing TKAs retrieved due to osteolysis/loosening, infection, stiffness, instability or malpositioning. Visual grading used stereomicroscopy to identify damage, and a grade was assigned based on extent and severity. Each damage mode was then mapped onto a photograph of the implant surface, and the area affected was calculated. Results Marked wear damage occurred on both surfaces, with burnishing, scratching, and pitting the dominant modes. Damage occurred over a large portion of both surfaces, exceeding the available articular borders in nearly 30% of implants. Wear of mobile-bearing surfaces included marked third-body debris. Damage on tibiofemoral and mobile-bearing surfaces was not correlated with patient BMI or component alignment. Damage on mobilebearing surfaces was positively correlated with length of implantation and was greater in implants removed for osteolysis or instability than in those removed for stiffness or infection. Conclusions Each bearing surface in mobile-bearing implants was damaged to an extent similar to that in fixedbearing implants, making the combined damage score higher than that for fixed-bearing implants. Mobile-bearing TKAs did not improve wear damage, providing another argument against the superiority of these implants over fixed-bearing implants.

Can Microcomputed Tomography Measure Retrieved Polyethylene Wear? Comparing Fixed-bearing and Rotating-platform Knees

“…The application of micro-CT to retrieved in vivo worn polyethylene liners provides additional data on retrievals, which have traditionally only been studied by characterization of surface wear modes [8,[10][11][12]16]. Our average wear of 58 mm 3 /year falls between the wear reported for knee simulators (Table 3) and retrieval studies (Table 4).…”

“…Surface damage has been studied in worn polyethylene retrievals using visual assessment grading scales [4,[10][11][12]16]. Condylar penetration has been measured radiographically [6,20,22].…”

“…However, measures of condylar penetration do not allow an analysis of penetration volume and are not necessarily an accurate measure of true wear because penetration does not account for creep or deformation. Analysis of retrieved components either at revision or postmortem allows the analysis of surface damage and changes in polyethylene thickness [4,7,8,[10][11][12]16]. Retrieval analysis is inherently more accurate and detailed than radiographic analysis of condylar penetration and does provide more insight into wear.…”

Does Increased Topside Conformity in Modular Total Knee Arthroplasty Lead to Increased Backside Wear?

“…Therefore, clinical performance of knee bearings is often based on visual assessment of bearing surfaces rather than actual material lost [7,8,10]. Rather than surface deformation features, it is the polyethylene debris from both the abrasive and adhesive wear on the backside surface of the tibial inserts that is implicated as a cause for wear debris osteolysis [11,13].…”

Comparison of Fixed and Mobile-Bearing Total Knee Arthroplasty at a Mean Follow-up of 116 Months

“…Despite these theoretical advantages 16 , higher cost and reported problems of joint stiffness and failure due to instability are among the barriers to wide adoption of mobilebearing knee designs 17 . Furthermore, mobile-bearing total knee arthroplasty has not been shown to be clinically superior or more durable compared with fixed-bearing total knee arthroplasty [18][19][20][21] .…”