gms | German Medical Science

Objectives: At present ceramic on highly crosslinked Polyethylene (HXLPE) is the most common bearing combination being in use for primary THAs in the United States. HXLPE inlays show excellent survival rates in the short and mid-term, while the linear wear rate is significantly lower compared to non-crosslinked UHMWPE inlays. For UHMW-PE increased wear has been reported for patients with an increase in femoral offset of more than 5mm after THA. However, no association has been reported for hip geometry reconstruction and HXLPE wear.

Therefore the present study aimed 1) to determine the polyethylene wear of 32mm ceramic heads with HXLPE inlays up to 10 years postoperatively and 2) to identify patient and surgery-related factors affecting the wear rate of HXLPE inlays.

Methods: A cohort of 101 patients with 101 THAs performed between 01/2008 and 12/2009 using a 32-mm ceramic head (Biolox®) and HXLPE liners (Durasul®) were retrospectively studied. Demographic data, patient reported outcome measures (PROMs), patient physical activity scores (UCLA score) and radiographic parameters (postoperative change in femoral offset, leg-length difference (LLD) and cup inclination/anteversion) were evaluated. The wear rate was determined by two reviewers, blinded to each other, using a validated software (PolyWare Rev 8, Draftware Inc). A linear regression model was used to identify patient and surgery-related factors on PE-wear.

Results and Conclusion: The mean age at surgery was 58,0 years (SD 11,4) and at a mean follow up of 7.7 years (SD 0.6 years) no osteolysis or aseptic loosening were detected. After ten years, the mean linear wear rate of HXLPE liners was 0.059mm/y (SD 0.031mm/y) after an initial bedding-in phase of 1 year after surgery (Figure 1 [Fig. 1]), being well below the osteolysis relevant threshold of 0.1 mm/year. The regression analysis demonstrated that age at surgery, BMI, cup inclination/anteversion and the UCLA score were not associated with the linear wear rate for the HXLPE inlays (Table 1 [Tab. 1]). Only the change in femoral offset showed a significant correlation with the wear rate of HXLPE liners, although the clinical effect size was very low (R²= 0.1) (Figure 1 [Fig. 1]).

Patient demographics, physical activity, implant orientation and hip geometry reconstruction did not clinically relevantly affect the linear wear rate of HXLPE inlays 10 years after THA. Our study suggests, that in contrast to conventional UHMWPE inlays, hip arthroplasty surgeons may be concerned less about HXLPE wear, allowing to focus on the reconstruction of offset and leg-length in order to achieve good joint stability, minimized leg length difference and optimum patient satisfaction after THA.