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Radiostereometric analysis (RSA) has evolved as gold standard in the evaluation of wear and especially as regards novel hip implant materials. However, several cup shell materials and articulation types used in total hip arthroplasty (THA) cannot be studied due to poor radiographic visibility of the femoral head (FH). We addressed this problem with use of a point transfer function in the RSA software to indirectly measure FH translations with use of stem markers. In a base examination, the stem marker segment and cup center, as an approximation for the FH center position, were mathematically coupled. Thereafter, in subsequent examinations, we used the point transfer function to calculate FH positions from stem marker positions. To determine the variance of the difference of directly and indirectly measured FH positions, four stem marker configurations were studied in THAs with radiographically visible FHs. For the axis with least variance we also compared directly and indirectly measured translation up to 7 years. Finally, we applied the method in a ceramic‐on‐ceramic (COC) articulation and measured proximal translation up to 7 years and also estimated precision. Vertical translations had the smallest variation between measured and calculated FH position. Directly and indirectly measured vertical FH translation correlated well but indirect measurements had increased variance. Proximal steady‐state penetration rate in uncemented COC THA was −0.003 (SD 0.021) mm/year with 99% precision along the vertical axis measuring 0.34 mm. The point transfer function can be used to measure proximal FH penetration, but with less precision than direct RSA. [ABSTRACT FROM AUTHOR]

Background: In an earlier study with a 2-year follow-up of uncemented cups, we had reported low femoral-head penetration of vitamin E-infused highly cross-linked polyethylene liners (E1) compared with highly cross-linked liners without vitamin E (ArComXL). We studied the penetration rate of E1 compared with that of ArComXL, with a focus on changes occurring between 2 and 5 years after total hip arthroplasty.Methods: In this randomized controlled study, we performed radiostereometric analysis of the penetration rate up to 5 years in 63 hips.Results: During the total period of observation, the median proximal penetration for E1, 0.13 mm (mean, 0.11 mm [95% confidence interval (CI), 0.08 to 0.14 mm]), was lower than that for ArComXL, 0.20 mm (mean, 0.22 mm [95% CI, 0.17 to 0.26 mm]). The median proximal penetration rate between 2 and 5 years was 0.02 mm/yr (mean, 0.01 mm/yr [95% CI, 0.01 to 0.02 mm/yr]) for E1 and 0.04 mm/yr (mean, 0.04 mm/yr [95% CI, 0.03 to 0.05 mm/yr) for ArComXL. The corresponding median total (i.e., 3-dimensional resultant) penetration rates were 0.04 mm/yr (mean, 0.04 mm/yr [95% CI, 0.03 to 0.05 mm/yr]) for E1 and 0.07 mm/yr (mean, 0.08 mm/yr [95% CI, 0.06 to 0.10 mm/yr]) for ArComXL.Conclusions: From years 2 to 5, we observed increased penetration in both groups. The penetration rate was higher for ArComXL, resulting in more proximal and total penetration at 5 years than for E1.Level Of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence. [ABSTRACT FROM AUTHOR]

Background and purpose — Most registry studies regarding highly crosslinked polyethylene (XLPE) have focused on the overall revision risk. We compared the risk of cup and/or liner revision for specific cup and liner designs made of either XLPE or conventional polyethylene (CPE), regarding revision for any reason and revision due to aseptic loosening and/or osteolysis. Patients and methods — Using the Nordic Arthroplasty Register Association (NARA) database, we identified cup and liner designs where either XLPE or CPE had been used in more than 500 THAs performed for primary hip osteoarthritis. We assessed risk of revision for any reason and for aseptic loosening using Cox regression adjusted for age, sex, femoral head material and size, surgical approach, stem fixation, and presence of hydroxyapatite coating (uncemented cups). Results — The CPE version of the ZCA cup had a risk of revision for any reason similar to that of the XLPE version (p = 0.09), but showed a 6-fold higher risk of revision for aseptic loosening (p < 0.001). The CPE version of the Reflection All Poly cup had an 8-fold elevated risk of revision for any reason (p < 0.001) and a 5-fold increased risk of revision for aseptic loosening (p < 0.001). The Charnley Elite Ogee/Marathon cup and the Trilogy cup did not show such differences. Interpretation — Whether XLPE has any advantage over CPE regarding revision risk may depend on the properties of the polyethylene materials being compared, as well as the respective cup designs, fixation type, and follow-up times. Further research is needed to elucidate how cup design factors interact with polyethylene type to affect the risk of revision. [ABSTRACT FROM PUBLISHER]

Background: Highly cross-linked polyethylene infused with vitamin E (E-poly) was developed to increase oxidative resistance without affecting mechanical properties. We evaluated this type of polyethylene in a randomized clinical study that used radiostereometric analysis. Our objective was to compare the early-term femoral head penetration of an E-poly liner with that of a heat-treated polyethylene liner, ArComXL. We hypothesized that the clinical outcome at two years following total hip arthroplasty would be unaffected by the choice of polyethylene. Methods: In this prospective study, sixty-one patients (seventy hips) with noninflammatory hip osteoarthritis and a median age of fifty-eight years were randomized to receive either an implant with an E-Poly or a heat-treated highly crosslinked polyethylene liner. The patients were followed for two years and evaluated at three time points (three months, one year, and two years). Results: The median proximal penetration in the E-poly group increased from 0.04 mm at three months to 0.06 mm at two years of follow-up. Corresponding values for the ArComXL group were 0.03 mm and 0.10 mm. In both groups, significantly increased penetration was observed between three months and two years (E-poly, p = 0.02; ArComXL, p < 0.001), but between one and two years, the increase was significant only in the control group (E-poly, p = 0.23; ArComXL, p = 0.002). Conclusions: The femoral head penetration of E-poly was very low at two years. Whether the increase observed between three months and two years was caused by creep, deformation, wear, or a combination of these cannot be determined by our study. There were no significant differences observed in femoral head penetration rates between E-poly and ArComXL. Currently, the theoretical advantages of E-poly remain to be confirmed. [ABSTRACT FROM AUTHOR]

Background: Polyethylene (PE) wear particles are believed to cause aseptic loosening and thereby impair function in hip arthroplasty. Highly crosslinked polyethylene (XLPE) has low short- and medium-term wear rates. However, the long-term wear characteristics are unknown and it is unclear whether reduced wear particle burden improves function and survival of cemented hip arthroplasty. Questions/purposes: We asked whether XLPE wear rates remain low up to 10 years and whether this leads to improved implant fixation, periprosthetic bone quality, and clinical function compared to conventional PE. Methods: We randomized 60 patients (61 hips) to receive either PE or XLPE cemented cups combined with a cemented stem. At 10 years postoperatively, 51 patients (52 hips) were evaluated for polyethylene wear and component migration estimation by radiostereometry, for radiolucent lines, bone densitometry, and Harris hip and pain scores. Revisions were recorded. Results: XLPE cups had a lower mean three-dimensional wear rate between 2 and 10 years compared to conventional PE hips: 0.005 mm/year versus 0.056 mm/year. We found no differences in cup migration, bone mineral density, radiolucencies, functional scores, and revision rate. There was a trend toward improved stem fixation in the XLPE group. The overall stem failure rate was comparably high, without influencing wear rate in XLPE hips. Conclusions: XLPE displayed a low wear rate up to 10 years when used in cemented THA, but we found no clear benefits in any other parameters. Further research is needed to determine whether cemented THA designs with XLPE are less prone to stem loosening. Level of Evidence: Level I, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence. [ABSTRACT FROM AUTHOR]

Background and purpose The reported outcomes of hip resurfacing arthroplasty (HRA) vary. The frequency of this procedure in Denmark, Norway, and Sweden is low. We therefore determined the outcome of HRA in the NARA database, which is common to all 3 countries, and compared it to the outcome of conventional total hip arthroplasty (THA). Methods The risk of non-septic revision within 2 years was analyzed in 1,638 HRAs and compared to that for 172,554 conventional total hip arthroplasties (THAs), using Cox regression models. We calculated relative risk (RR) of revision and 95% confidence interval. Results HRA had an almost 3-fold increased revision risk compared to THA (RR = 2.7, 95% CI: 1.9-3.7). The difference was even greater when HRA was compared to the THA subgroup of cemented THAs (RR = 3.8, CI: 2.7-5.3). For men below 50 years of age, this difference was less pronounced (HRA vs. THA: RR = 1.9, CI: 1.0-3.9; HRA vs. cemented THA: RR = 2.4, CI: 1.1-5.3), but it was even more pronounced in women of the same age group (HRA vs. THA: RR = 4.7, CI: 2.6-8.5; HRA vs. cemented THA: RR = 7.4, CI: 3.7-15). Within the HRA group, risk of non-septic revision was reduced in hospitals performing ≥ 70 HRAs annually (RR = 0.3, CI: 0.1-0.7) and with use of Birmingham hip resurfacing (BHR) rather than the other designs as a group (RR = 0.3, CI: 0.1-0.7). Risk of early revision was also reduced in males (RR = 0.5, CI: 0.2-0.9). The femoral head diameter alone had no statistically significant influence on the early revision rate, but it eliminated the significance of male sex in a combined analysis. Interpretation In general, our results do not support continued use of hip resurfacing arthroplasty. Men had a lower early revision rate, which was still higher than observed for all-cemented hips. Further follow-up is necessary to determine whether HRA might be useful as an alternative in males. [ABSTRACT FROM AUTHOR]