When Forced to Choose, Larger Femoral Head Size Confers Greater Protection Against Risk for Dislocation than a Lipped Acetabular Liner.

BACKGROUND

Increasing femoral head size or using lipped polyethylene acetabular liners both reduce revision risk due to dislocation after total hip arthroplasty (THA). At some cup sizes, surgeons must choose between larger heads or lipped liners. This study compares 32-mm heads with 10° lipped liners against 36-mm heads with neutral liners for stability and revision risk.

METHODS

A national registry was queried for primary posterior-approach THAs. A total of 24,921 procedures were included: 17,386 with 32-mm femoral heads and 10° lipped cross-linked polyethylene liners, and 7,535 with 36-mm femoral heads and neutral cross-linked polyethylene liners. Kaplan-Meier analysis, multivariable logistic regressions, and t-tests evaluated 90-day, 2-year, and 8-year revision rates due to dislocation. A subanalysis was performed for patients who had a body mass index ≥ 30. The secondary outcomes included all-cause revision, infection, aseptic loosening, and periprosthetic fracture.

RESULTS

The 90-day, 2-year, and 8-year rates of revision for dislocation were higher in the 32-mm and 10° lipped liner cohort. The Kaplan-Meier curve analyses demonstrated the rate of revision for dislocation was significantly higher in the 32-mm and 10° lipped liner group during the first month following THA (hazard ratio, 5.58; P = 0.019), but was not significant at any later time points. Among obese patients, those who received 32-mm heads and lipped liners had over three times higher odds of revision for persistent dislocation throughout eight years of follow-up hazard ratio, 3.28; P = 0.012).

CONCLUSIONS

With a 50-mm acetabular cup, a 36-mm femoral head and a neutral acetabular liner confer greater protection from revision of THA due to dislocation, particularly during the first postoperative month. In obese patients, the elevated dislocation risk with 32-mm heads and lipped liners persists throughout 8-year follow-up, highlighting the sustained clinical benefit of larger head size in this population.