Background: Studies have shown that increased femoral head size reduces the risk of dislocation in primary total hip arthroplasty (THA), but there has been limited research on femoral head sizes greater than 36 mm.
Methods: The American Joint Replacement Registry was utilized to evaluate all primary THA cases in Medicare patients aged 65 years and older who had a femoral head size of 32, 36, or ≥ 40 mm between 2012 and 2020. Patients who received a ≥ 40-mm head were more likely to be men and had a higher Charlson comorbidity index (CCI, P < 0.001). Multivariate analyses were performed to adjust for age, sex, race, femoral head composition, and CCI. Cox's proportional hazards models were used to compare differences in revision between groups.
Results: Of 319,531 total THA cases, 84,524 (26.4%) used a 32 mm, 211,814 (66.3%) used a 36 mm, and 23,193 (7.3%) used ≥ 40-mm femoral head. When compared to 32-mm heads, 36-mm heads had significantly lower rates of revision for dislocation (32 mm: 0.68%, 36 mm: 0.46%, P < 0.001). Femoral heads ≥ 40 mm were not associated with a decreased rate of revision for dislocation (0.51%) when compared to 32 and 36 mm heads. However, femoral heads ≥ 40 mm were associated with an increased risk of all-cause revision (32 mm: 2.55%, 36 mm: 2.37%, 40 mm: 2.78%, P < 0.001) and revision for infection (32 mm: 0.43%, 36 mm: 0.53%, 40 mm: 0.82%, P < 0.001) compared to 32 and 36 mm heads.
Conclusions: Large femoral heads (≥ 40 mm) do not decrease revision for dislocation in primary THA but were associated with an increased risk of all-cause revision and revision for infection. Although demographic and comorbidity variables were controlled in our multivariate analysis, more men and higher CCI in ≥ 40-mm head patients may represent a population with a greater presurgical risk for complications. More research on ≥ 40-mm heads is warranted before widespread adoption.
Keywords: dislocation; head size; hip arthroplasty; instability; revision.
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