Revision of TKA as a result of polyethylene wear is decreasing, but long-term wear performance of polyethylene is still a topic of interest to surgeons and device manufacturers seeking to improve longevity. Measuring wear of modern, wear-resistant implants has been described using radiostereometric analysis (RSA). Performing in vivo measurements would establish whether implant retrieval studies are representative of wear in well-performing knees.
For a single knee implant system, we sought to determine (1) the linear wear rate using RSA; (2) the association between demographic factors and wear rate; and (3) the association between limb alignment and wear rate.
A total of 49 patients with a minimum followup of 10 years (median, 12 years; range, 10-20 years) were retrospectively selected. During the examined period, 4082 TKAs were performed of which 2085 were the implant examined in this study. There were 71 of these patients who met the criteria including an available full-leg radiograph postoperatively, and 34 of these patients returned for examination along with 15 additional from a separate RSA study that also met the criteria. All patients received a posterior-stabilized, cobalt-chromium-on-conventional polyethylene total knee implant from a single implant system, which was the most commonly used at our institution at the time. Patients underwent standing RSA examinations from 0° to 120° of flexion at a single time point without the use of marker beads. Linear wear rates (including creep) were measured based on intersections between the femoral component and tibial insert models. Associations between wear and patient age at surgery, sex, height, weight, body mass index, tibial insert size, and limb alignment were examined.
Using the maximum linear wear rate from any flexion angle, the lateral rate was 0.047 mm/year (interquartile range [IQR], 0.034-0.066 mm/year) and the medial rate was 0.052 mm/year (IQR, 0.040-0.069 mm/year). Using the median of the linear wear rates across all flexion angles, the lateral rate was 0.027 mm/year (IQR, 0.017-0.046 mm/year) and the medial rate was 0.038 mm/year (IQR, 0.022-0.054 mm/year). This rate for males was 0.049 mm/year medially (IQR, 0.042-0.077 mm/year) and 0.032 mm/year laterally (IQR, 0.026-0.059 mm/year), and for females was 0.027 mm/year medially (0.016-0.039 mm/year) and 0.020 mm/year laterally (IQR, 0.013-0.032 mm/year). The wear rate for males was greater medially (difference = 0.022 mm/year, p < 0.001) and laterally (difference = 0.012 mm/year, p = 0.008). There were associations between greater wear and increasing height (ρ = 0.48, p < 0.001 medially and ρ = 0.30, p = 0.04 laterally), decreasing body mass index (ρ = -0.31, p = 0.03 medially), and greater implant size (ρ = 0.34, p = 0.02 medially). Increasingly varus leg alignment was associated with greater medial wear (ρ = 0.33, p = 0.02).
Greater wear rates were associated with demographic factors and leg alignment. Further RSA wear studies of other modern implant systems would provide complementary information to retrieval studies and valuable data on wear resistance.
Good wear resistance was demonstrated by well-performing implants in patients at long-term followup with wear magnitudes in agreement with reported values from retrieval studies.
M. G. Teeter, R. W. McCalden, S. J. MacDonald, B. A. Lanting, D. D. Naudie, Department of Surgery, Schulich School of Medicine & Dentistry, Western University and London Health Sciences Centre, London, Ontario, Canada
M. G. Teeter, J. Wihlidal, X. Yuan, Department of Medical Biophysics, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
M. G. Teeter, Department of Surgery, Schulich School of Medicine & Dentistry, Western University and London Health Sciences Centre, 339 Windermere Road, London, Ontario, Canada, N6A 5A5, email: firstname.lastname@example.org
This study was supported by the Canadian Institutes of Health Research (New Investigator Award; MGT) and the Ontario Ministry of Research (Ontario Research Fund; MGT). The institution of one or more of the authors (MGT, RWM, SJM, BAL, DDN) has received during the study period funding from Smith & Nephew (Memphis, TN, USA), DePuy (Warsaw, IN, USA), Stryker (Mahwah, NJ, USA), Zimmer (Warsaw, IN, USA), and Microport (Arlington, TN, USA). One of the authors certifies that he (RWM) or a member of his immediate family has received during the study period an amount of USD 100,001 to USD 1,000,000 from Smith & Nephew. One of the authors certifies that he (SJM) or a member of his immediate family has received during the study period an amount of USD 100,001 to USD 1,000,000 from DePuy. One of the authors certifies that he (BAL) or a member of his immediate family has received during the study period an amount of less than USD 10,000 from DePuy and Integra (Plainsboro, NJ, USA), an amount of less than USD 10,000 from Intellijoint (Waterloo, Ontario, Canada), and an amount of less than USD 10,000 from Stryker; and grants in an amount of USD 10,001 to USD 100,000 from DePuy, an amount of USD 10,001 to USD 100,000 from Microport, an amount of USD 10,001 to USD 100,000 from Stryker, and an amount of less than USD 10,000 from Zimmer. One of the authors certifies that he (DDN) or a member of his immediate family has received during the study period an amount of USD 10,001 to USD 100,000 from Exactech (Gainesville, FL, USA), an amount of USD 10,001 to USD 100,000 from Smith & Nephew, an amount of USD 10,001 to USD 100,000 from Stryker, and an amount of USD 10,001 to USD 100,000 from Zimmer.
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.
Clinical Orthopaedics and Related Research® neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA approval status, of any drug or device before clinical use.
Each author certifies that his institution approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.
Received November 30, 2017
Accepted June 15, 2018