Third-Generation Medium Cross-Linked Polyethylene Demonstrates Very Low Wear in Total Hip Arthroplasty

Wear of Third-Generation Cross-Linked Polyethylene in Primary Total Hip Arthroplasty: A 10-Year Analysis

BACKGROUND

Sequential modifications to the manufacturing process of highly cross-linked polyethylene (HXLPE) have improved the wear resistance and implant survival of these liners in total hip arthroplasty (THA). However, no study has examined the long-term (mean 10 year) wear rates and clinical outcomes of third-generation HXLPE in THA. The aim of our study was to report the longest-to-date analysis of wear rates and clinical outcomes of a third-generation HXLPE liner.

METHODS

A series of 133 THAs using a specific HXLPE acetabular liner were retrospectively evaluated. Linear and volumetric wear rates were determined using a validated radiographic technique and clinical outcomes were analyzed. Multivariate analyses were performed to determine risk factors for accelerated wear.

RESULTS

At a mean follow-up of 10.4 years (range, 8 to 13.4), the mean linear wear rate was 0.0172 mm/year and the mean volumetric wear rate was 16.99 mm3/year. There were no instances of osteolysis or mechanical failures at any time point and there was a 100% acetabular component survival rate. Younger age and use of offset liners were independent risk factors for increased wear (P < .01 for both).

CONCLUSIONS

Our series of a third-generation HXLPE demonstrated very low wear rates and excellent implant survival at a mean of 10.4 years following primary THA. Future comparative studies at the 15- and 20-year follow-up timepoints are necessary to determine if such findings translate to true improvements in the tribological properties and longevity of these liners when compared to previous generations of HXLPE liners.

Polyethylene thickness does not influence aseptic revision rate with highly cross-linked liners in THA with 36-mm femoral heads

BACKGROUND

To reduce the risk of dislocation, larger head size can be used in total hip arthroplasty (THA). However, larger head size leads to thinner acetabular liners. With conventional polyethylene, thickness of >8 mm has been advocated to reduce stress and wear rate of the polyethylene. Modern polyethylene has become more wear-resistant. In this study, we investigated if the thickness of sequentially cross-linked polyethylene (XLPE) liners is associated with failure of THA in the medium term.

PATIENTS AND METHODS

3654 THAs were included (2009-2016), in which THA was performed with a XLPE liner in combination with a 36-mm femoral head. Patient and surgical characteristics were collected. We compared implant survival of THA with thin liners (<7.9 mm) and thick liners (⩾7.9 mm) with a Kaplan Meier survival analysis at 5 years, median follow-up and 10 years of follow-up with and point aseptic loosening and performed a multivariate analysis to estimate hazard ratios (HR).

RESULTS

Median follow-up was 7.7 years (IQR 5.6-9.8). In total, 179 revision procedures were performed, where 82 revisions (46%) were performed for aseptic loosening. The survival rate at 5 years, median and 10 years of follow-up showed no statistically significant difference in implant survival. The survival rate at 10 years follow-up was for thin liners 97.1% (95% CI, 96.3-97.9) and for thick liners 98.2% (95% CI, 97.4-99.0) in the aseptic loosening group (chi-square 2.55; p = 0.11).The adjusted HR for thick liners (⩾7.9 mm) was 0.65 (95% CI, 0.38-1.08) compared with the thin liners (<7.9 mm), which was not significantly different.

CONCLUSIONS

From this single-centre retrospective study it appears that thinner polyethylene liners are well tolerated when using second-generation highly cross-linked polyethylene. Thickness of the XLPE liners did not influence the risk of aseptic loosening of the implants in the medium term.

In Vitro Analysis of Wearing of Hip Joint Prostheses Composed of Different Contact Materials

Cobalt-chromium-molybdenum alloy (CoCrMo) and ceramic are the two most common materials for the femoral head in hip joint prostheses, and the acetabular liner is typically made from ultra-high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (XLPE), or highly cross-linked polyethylene blended with Vitamin E (VEXLPE). The selection of suitable materials should consider both wear performance and cost-effectiveness. This study compared the wear rate between different friction pairs using a hip joint simulator and then recommended a suitable prosthesis based on the corresponding processing technology and cost. All wear simulations were performed in accordance with ISO 14242, using the same hip joint simulator and same test conditions. This study found that when using the same material for the femoral head, the XLPE and VEXLPE liners had a lower wear rate than the UHMWPE liners, and the wear rate of the XLPE liners increased after blending with Vitamin E (VEXLPE). There was no significant difference in the wear rate of XLPE when using a CoCrMo or ceramic head. Considering the wear rate and cost-effectiveness, a CoCrMo femoral head with an accompanying XLPE liner is recommended as the more suitable combination for hip prostheses.