Abstract
Aim
To assess the effect of the bearing surface and head size on the survival of total hip replacements with modern bearing surface combinations.
Methods
We combined the NJR dataset with polyethylene manufacturing properties as supplied by the manufacturers to sub-divide polyethylene into conventional (PE) and highly crosslinked (XLPE). Cause specific and overall reasons for revisions were analysed using Kaplan-Meier and multi-variate Cox proportional hazard regression survival analyses. The bearing surface analysis was repeated in patients undergoing THR under the age of 55.
Results
A total of 337,786 primary THR cases were included with an associated 5,618 revisions. Head size was grouped in <= 28mm (group A), 32mm (group B) and >=36mm (group C). A Cox regression model adjusted for age, gender, bearing combination and stem fixation was used to provide Hazard Ratios (HR). With Group C as reference, revision for all causes in Group A had a HR 1.07 (95%CI 0.99, 1.15) and in Group B HR 0.92 (0.86, 0.98). In patients <55y of age, with MoP as reference, Hazard Ratio for MoXLPE was 0.77 (0.59, 1.01), CoC 0.64 (0.52, 0.78), CoXLPE 0.61 (0.47, 0.78), CoP 0.50 (0.36, 0.70) and CMoXLPE 0.47 (0.30, 0.76).
Conclusion
When combined with modern bearing combinations, the use of femoral heads of 36mm or larger was associated with a decreased cumulative incidence of revision for dislocation and an increased incidence of revision for aseptic loosening. In patients under the age of 55, CMoXLPE performed best at maximum follow up of 11 years.
