Does the femoral offset affect replacements? The results from a National Joint Registry

Femoral component offset influences the torque forces exerted on a femoral stem and may therefore adversely affect femoral component survival. This study investigated the influence of femoral component offset on revision rates for primary total hip replacements (THR) registered on the New Zealand Joint Registry (NZJR).

There were 106,139 primary THRs registered, resulting in 4960 revisions for any cause. There were 46,242 THRs performed using the five commonest femoral components listed on the NZJR. A total of 41,100 were done for primary osteoarthritis of which 40,548 had all the offset information available for analysis. We defined low offset as < 42 mm, standard as 42-48 mm and high offset as > 48 mm offset and examined revision rates according to the reasons for revision. We performed survival analyses for both cemented and uncemented femoral components grouped by the different offsets.

The all-cause revision rate was 0.54/100 component years (cys). Stems with < 42 mm offset had a revision rate of 0.58/100 cys (mean 0.58; 95% confidence interval (CI) 0.53-0.63), 42-48 mm offset 0.47 (95% CI 0.43-0.52) and > 48 mm offset 0.67 (95% CI 0.57-0.79). There was no significant difference in all-cause revision rates between varying stem offsets in uncemented stems adjusting for age and gender. In cemented stems both high and low offset stems were more likely to be revised. Uncemented stems of all offsets were more likely to undergo revision for femoral fracture.

Femoral component offset affects the overall all-cause revision rate of the most commonly used cemented stem, but not uncemented stem designs. In cemented stems offset influences the rate of revision for loosening and periprosthetic fractures.