Functional implications of femoral offset following hemiarthroplasty for displaced femoral neck fracture

Purpose Inadequate reconstruction of femoral offset after total hip arthroplasty (THA) is associated with unfavourable outcomes, but its importance following hemiarthroplasty for displaced femoral neck fracture is unknown. Methods Our study examined the correlation between reconstructed femoral offset and functional outcome 12 months after post traumatic hemiarthroplasty in 126 prospectively enrolled elderly patients. Rotation-corrected femoral offset (FORC), relative femoral offset (FORL) and contralateral femoral offset (FOC) were measured on anteroposterior radiographs. The Harris Hip Score (HHS) was the primary outcome measure; the timed up and go (TUG) test and Lawton instrumental activities of daily living (IADL) score were secondary outcomes. Correlations were sought using the Spearman correlation coefficient (r). Sample size was calculated using an Altman nomogram, with the power set at 80 %, the significance level of 0.05 and a standardised difference of 0.75. Results The mean reconstructed FORC was 41 mm (17-67 mm) and showed a linear relationship and excellent correlation with the FOC. At 12 months, we found a significant positive correlation between FORC and HHS (r = 0.303, p = 0.025) and IADL (r = 0.325, p = 0.013), but not TUG (r = -0.026, p = 0.863). These findings were confirmed by bivariate and multivariate correlation between FORL and functional outcome parameters. Conclusions We found a clinically relevant relationship between femoral offset and functional outcome after hemiarthroplasty in elderly patients, comparable with that of THA, for treating osteoarthritis.