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

Abstract

Background Modular metal-backed tibia components allow surgeons intraoperative flexibility. Although it is known that modular tibia components introduce the possibility for backside wear resulting from relative motion between the polyethylene insert and the tibial baseplate, it is not known to what degree variability in the conformity of the tibial polyethylene liner itself might contribute to backside wear. Questions/purposes The purpose of this study was to determine whether a flat, cruciate-retaining tibial polyethylene bearing generates less backside wear than a more conforming (curved) tibial polyethylene bearing in an analysis of specimens explanted during revision surgery. MethodsThe study included 70 total knee inserts explanted at revision surgery, all implanted and explanted by the same surgeon. Two different cruciate-retaining insert options in an otherwise similar knee system were used: one with a curvedon-flat (17) articular geometry and one with a highly conforming curved-on-curved design (53); both groups were sequential cohorts. The composite backside wear depth for the insert as well as the volume of backside wear was measured and compared between groups. Results The median linear backside-normalized wear for the posterior lipped inserts was 0.0063 mm/year (range, 0-0.085 mm/year), which was lower than for the curved inserts at 0.05 mm/year (range, 0.00003-0.14 mm/year) (p \ 0.001). The median calculated volumetric backsideOne of the authors (RS) has received consulting fees from Smith & Nephew (Memphis, TN, USA) (less than USD 10,000). One of the authors (RDS) has received consulting fees from DePuy (Warsaw, IN, USA) (less than USD 10,000) and royalties from DePuy (greater than USD 1,000,000). One or more of the authors (EMC, JHS) has received institutional funding from DePuy, ConforMIS (Bedford, MA, USA), and Biomet (Warsaw, IN, USA). All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research 1 editors and board members are on file with the publication and can be viewed on request. Clinical Orthopaedics and Related Research 1 neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDAapproval status, of any drug or device prior to clinical use. Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained. This work was conducted at the New England Baptist Hospital, Boston, MA USA. The biomechanical material analysis was conducted at the Thayer School of Engineering, Dartmouth College, Hanover, NH, USA. Conclusions In this retrieval study, more conforming tibial inserts demonstrated more backside-normalized wear than the flatter designs. This suggests that in this modular total knee arthroplasty design, higher articular conformity to address the issues of high bear...

Current Total Knee Designs: Does Baseplate Roughness or Locking Mechanism Design Affect Polyethylene Backside Wear?

“…This correlation is corroborated in multiple other retrieval studies [1,3,4,18]. There also are varying degrees of evidence that backside wear is increased by other implant factors such as polyethylene sterilization in noninert gas [2,5,6,9,25,40], polyethylene manufacturing [16,27], tibial baseplate composition [3,4,7], conformity of the polyethylene articular surface [36], and polyethylene thickness [13,44]. In some studies, patient factors such as longer time in vivo of the polyethylene [17,21,31], increased patient weight [8], male sex, and younger patient age [16] have been shown to increase backside wear.…”

The effects of presence of a backside screw hole on biotribological behavior of phospholipid polymer‐grafted crosslinked polyethylene

“…This study was subject to several limitations. First, we used a pin‐on‐disk test method, so the shapes of the pin‐and‐disk specimens were different from those of the joint replacements, whereas Schwarzkopf et al reported that the conformity of the bearing surface affected the backside damage of PE . However, the roughness of the bearing surface of the pin‐and‐disk specimens was similar to that of the artificial joint products.…”

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

“…The polyethylene is often secured to the tray by one of a variety of proprietary locking mechanisms, comprising a fixed‐bearing device. A frequently cited reason for failure of these knee replacements is wear of articular and/or backside (non‐articular) surface of this polyethylene tibial insert …”

“…For knee replacement patients, the sub‐micron polyethylene debris produced by wear of the tibial insert can cause a number of negative outcomes including synovitis, aseptic loosening, and osteolysis . Although in fixed‐bearing tibial constructs the polyethylene is captured by the metal tray, previous studies have indicated that the backside surface of the tibial insert can move relative to the tray, and this micro‐motion is a potential source of significant debris .…”