TITLE:
Wear Performance of Materials Used in Artificial Hip Joints—1. THR Diameter/Wear Ratios in Artificial Hip Joints: A 63-Year Charnley Legacy
AUTHORS:
Ian C. Clarke, Evert J. Smith
KEYWORDS:
Total Hip Replacement (THR), Wear, Teflon, Ultra-High Molecular Weight Polyethylene (UHMWPE), Simulator Wear Dichotomy (SWD), Femoral Head Diameter, In Vitro Wear Simulation, Charnley Hip Arthroplasty
JOURNAL NAME:
Open Journal of Orthopedics,
Vol.16 No.7,
July
31,
2026
ABSTRACT: Following the 1956 introduction of polytetrafluoroethylene (PTFE) total hip replacements (THR), a concerning question was how much wear debris could periarticular tissues tolerate before onset of adverse reactions. John Charnley’s historical studies demonstrated that wear in PTFE (“Teflon”) bearings led to destructive hip lesions within 3 years. While smaller femoral heads somewhat reduced wear, Teflon debris remained intolerable. In 1962 Charnley’s laboratory identified polyethylene (UHMWPE) as a substantially more wear-resistant polymer, launching the Charnley low-friction arthroplasty (LFA) in 1962. Three important results were clear: 1) femoral head diameter is the major wear determinant, i.e. the Charnley Diameter-Wear effect (“CDW”), 2) laboratory studies demonstrated UHMWPE had superior wear resistance to PTFE, and 3) major differences existed between laboratory predictions and clinical wear data, a phenomenon we shall term Laboratory Wear Divergence (“LWD”). This review examines wear data published by four laboratories to evaluate reproducibility, accuracy, and relevance of historical wear studies (1956-1976). Charnley’s wear laboratory described Teflon:UHMWPE wear ratios ranging 200:1 to 500:1 (1969). The introduction of UCLA’s wear machine in 1978 provided a dramatic improvement in experimental procedures. Using gravimetric weight-loss measurements in bovine-serum lubricated studies, the UCLA method for 316SS:UHMWPE samples achieved a wear precision of 0.2 mm3/Mc (±15%). Despite this precision, the LWD wear ratio (1600:1) for PTFE:UHMWPE wear greatly exceeded Charnley’s clinical (16:1) and laboratory (200:1) ratios. Orthopedic Hospital of Los Angeles (OHLA) reported (1981) a simulator design that incorporated multi-directional motion using crossing-path wear (CPW) motion. The pilot PTFE study (28 mm THR) yielded exceptionally high wear (2100 mm3/Mc), representing a debris release of 180 mm3 per 24-hours and prompted termination of study. This PTFE simulator wear overshot the clinical 28 mm Teflon wear (1171 mm3/year), a ratio of 1.8:1. This PTFE:Teflon wear (laboratory vs clinical) will be designated “WRP”. Kinamed (1996) investigated the Charnley-diameter-wear effect (CDW) using Al2O3: UHMWPE THR (22.25, 26, 28 mm dia.). Assuming Charnley’s clinical report is typical of LFA (60 mm3/year), the UHMWPE simulator ratio PCR = 0.6:1, i.e. it undershot the clinical UHMWPE datum. The 32.8 mm3/Mc wear rate (28 mm THR) corresponded to a CDW ratio of 6.9%, closely matching the Teflon clinical CDW value (6.8%), demonstrating the head-diameter-wear phenomenon was also present in UHMWPE THR. LLUMC conducted 8 PTFE THR experiments using four THR diameters to evaluate precision and reproducibility in laboratory studies. All wear trends were linear, and the Charnley-Diameter-Wear algorithm was present with both CoCr and ceramic femoral heads and precision comparable to UCLA’s report. With simulator PTFE wear-rate (28 mm THR) averaging 4227 mm3/Mc and Kinamed’s UHMWPE study averaging 32.8 mm3/Mc, the THR laboratory ratio (LWD) was 160:1. The grand-average wear-rates (7-replicated PTFE studies) were in perfect linear accordance with the CDW algorithm but again overshot Charnley’s Teflon data (WRP ratio = 3.6:1). Thus, simulator THR wear was underestimated in UHMWPE bearings and overestimated in PTFE bearings. With the precision evident in computer-controlled simulators, and using Charnley’s wear algorithms as internal controls, the most likely laboratory-relevant parameter for improved clinical simulation would appear to be choice of bovine-serum lubricant.