Highly crosslinked polyethylene (XLPE) was introduced to decrease peri-prosthetic osteolysis related to polyethylene wear, a major reason for revision of total hip arthroplasty. There are few reports of wear and osteolysis at 10 years post-operatively. We asked the following questions: (1) What are the linear and volumetric wear rates of one remelted XLPE at 10–14 years using the Martell method? (2) What is the relationship between volumetric wear, femoral head size, and osteolysis? (3) What is the incidence of osteolysis using conventional radiographs with Judet views and the Martell method?. Methods We evaluated a previously reported cohort of 84 hips (72 patients) with one design of an uncemented acetabular component and one electron-beam irradiated, remelted XLPE at a mean follow-up of 11 years (range 10 to 14 years). Measurements of linear and volumetric wear were performed in one experienced laboratory by the Martell method and standard radiographs, with additional Judet views, were used to detect peri-prosthetic osteolysis. Statistical analysis of wear and osteolysis compared to head size was performed. Results The mean linear wear rate by the first-to-last method was 0.024 mm/year (median, 0.010 mm/year) and the mean volumetric wear rate by this method was 12.2 mm. 3. /year (median, 3.6 mm. 3. /year). We found no association between femoral head size and linear wear rate. However, there was a significant relationship between femoral head size and volumetric wear rates, with 36/40 mm femoral heads having significantly higher volumetric wear (p=0.02). Small osteolytic lesions were noted in 12 hips (14%), but there was no association with head size, acetabular component position, or linear or volumetric wear rates. Conclusion This uncemented acetabular component and this particular remelted XLPE had low rates of linear and volumetric wear. Small osteolytic lesions were noted at 10 to 14 years, but were not related to femoral head size, linear or volumetric wear rates

Background. Wear and fatigue damage to polyethylene components remain major factors leading to complications after total knee and unicompartmental arthroplasty. A number of wear simulations have been reported using mechanical test equipment as well as computer models. Computational models of knee wear have generally not replicated experimental wear under diverse conditions. This is partly because of the complexity of quantifying the effect of cross-shear at the articular interface and partly because the results of pin-on-disk experiments cannot be extrapolated to total knee arthroplasty wear. Our premise is that diverse experimental knee wear simulation studies are needed to generate validated computational models. We combined five experimental wear simulation studies to develop and validate a finite-element model that accurately predicted polyethylene wear in high and low crosslinked polyethylene, mobile and fixed bearing, and unicompartmental (UKA) and tricompartmental knee arthroplasty (TKA). Methods. Low crosslinked polyethylene (PE). A finite element analysis (FEA) of two different experimental wear simulations involving TKA components of low crosslinked polyethylene inserts, with two different loading patterns and knee kinematics conducted in an AMTI knee wear simulator: a low intensity and a high intensity. Wear coefficients incorporating contact pressure, sliding distance, and cross-shear were generated by inverse FEA using the experimentally measured volume of wear loss as the target outcome measure. The FE models and wear coefficients were validated by predicting wear in a mobile bearing UKA design. Highly crosslinked polyethylene (XLPE). Two FEA models were constructed involving TKA and UKA XLPE inserts with different loading patterns and knee kinematics conducted in an AMTI knee wear simulator. Wear coefficients were generated by inverse FEA. Results. Predicted wear rates were within 5% of experimental wear rates during validation tests. Unicompartmental mobile bearing back-side wear accounted for 46% of the total wear in the mobile bearing. Wear during the swing phase was 38% to 44% of total wear. Discussion & Conclusions. Crosslinking polyethylene primarily decreased (by nearly 10-fold) the wear generated by cross-shear. This result can be explained by the reduced propensity of crosslinked polyethylene molecules to orient in the dominant direction of sliding. A highly crosslinked fixed-bearing polyethylene insert can provide high wear performance without the increased risk for mobile bearing dislocation. Finite element analysis can be a robust and efficient method for predicting experimental wear. The value of this model is in rapidly conducting screening studies for design development, assessing the effect of varying patient activity, and assessing newer biomaterials. This FEA model was experimentally validated but requires clinical validation

Introduction. Highly crosslinked ultrahigh-molecular-weight polyethylene (XLPE) reduces wear and osteolysis in total hip arthroplasty, but it is unclear if XLPE will provide the same clinical benefit in total knee arthroplasty (TKA). Adhesive and abrasive wear generally dominate in polyethylene acetabular components, whereas fatigue wear is an important wear mechanism in polyethylene TKA tibial inserts. The wear resistance of XLPE depends on the crosslink density of the material, which may decrease during in vivo mechanical loading, leading to more wear and increased oxidation. To examine this possibility, we measured crosslink density and oxidation levels in loaded and unloaded locations of retrieved tibial inserts to evaluate the short-term performance of XLPE material in TKA. Materials and Methods. Forty retrieved XLPE tibial inserts (23 remelted, 17 annealed) retrieved after a mean time of 18 ± 14 months were visibly inspected to identify loaded (burnished) and unloaded (unburnished) locations on the plateaus of each insert using a previously published damage mapping method. For each insert, four cubes (3 mm3) were cut from loaded and unloaded surface and subsurface locations (Fig. 1). Swell ratio testing was done according to ASTM F2214 to calculate crosslink density of the cubes. With a microtome, 200 μm sections were taken adjacent to the cubes and oxidation was assessed with Fourier transform infrared spectroscopy following ASTM F2102 (Fig. 2). Surface oxidation was measured in the sections adjacent the surface cubes and subsurface oxidation was measured in sections adjacent to the subsurface cubes. The effects of location (surface vs. subsurface in the loaded and unloaded regions) and thermal treatment (annealed vs. remelted) on crosslink density and oxidation were assessed with repeated measures generalized estimating equations (GEEs), with the implant treated as the repeated factor. Results are presented as means and 95% confidence intervals and the level of significance was α=0.05. Results. Crosslink density was associated with location within the polyethylene tibial inserts (p<0.001), while oxidation was associated with both location (p<0.001) and heat treatment (p=0.003). The loaded surface (location 1 in Fig. 1) had 13% lower crosslink density than all other locations (p<0.001 for each), and greater oxidation than all other locations (Fig. 3). Specifically, oxidation of the loaded surface was 0.29[0.17,0.40] greater (two times greater) than that of the unloaded surface (p < 0.001), whereas subsurface areas of loaded and unloaded regions differed by only 0.03[0.00,0.07] (p<0.022). Additionally, surface oxidation was over 7-fold greater than subsurface oxidation in the loaded region (difference: 0.56[0.44,0.68], p<0.001). Annealed XLPE had 2-fold greater oxidation than remelted XLPE (difference 0.159, 95% CI = 0.045, 0.126), and this was independent of location within the inserts. Conclusions. In vivo loading of XLPE decreased the crosslink density and increased the oxidation in areas that underwent wear and deformation at the articular surface of TKA inserts. Nonetheless, in these short term retrievals, no clinical complications were attributed to the change in material properties. However, if crosslink density continues to decrease with load over time, XLPE may not provide a clinical advantage over conventional polyethylene in TKA