PAPER 019: FEMORAL COMPONENT ORIENTATION IN HIP RESURFACING DONE WITH AND WITHOUT CT-FREE COMPUTER NAVIGATION

Abstract

Purpose: The aim of our study was to compare the precision and effectiveness of a CT-free computer navigation system against conventional technique (using a standard mechanical jig) in a cohort of unselected consecutive series of hip resurfacings.

Method: 139 consecutive Durom hip resurfacing procedures (51 navigated and 88 non-navigated) performed in 125 patients were analysed. All the procedures were done through a posterior approach by two surgeons and the study cohort include the hip resurfacings done during the transition phase of the surgeons’ adoption of navigation.

Results: There were no significant differences in the patients caracteristics, native neck-shaft angles, component sizes and blood loss between the two groups. There was a significant difference in the operative time between the two groups (111 minutes for the navigated group versus 105 minutes for the non-navigated group; p=0.048). There were 4 cases of notching in the non-navigated group. There was no other intra-operative technical problem in either of the groups nor were there any femoral neck fractures. No significant difference was found between the mean post-operative stem-shaft angles (138.5° for the navigated group versus 139.0° for the non navigated group, p=0.740). However there was a significant difference in the difference between the planned stem-shaft angle versus the post-operative stem-shaft angle (0.4° for the navigated group versus 2.1° for the non-navigated group; p=0.005). While, none of the cases in the navigated group had a post-operative stem-shaft angle with more than 5° deviation from the planned neck-shaft angle when compared to 33 cases (38%) in the non-navigated group (p≤0.001). For a given patient with a target angle set, it is estimated that positioning precision using the navigation is 1.3° +/− 0.9°, compared to 4.4° +/− 3.6° without navigation (p< 0.0001).

Conclusion: Hip resurfacing is a technically demanding procedure with a steep learning curve. Varus placement of the femoral component and notching have been recognised as important factors associated with early failures following hip resurfacing. While conventional instruments allowed reasonable alignment of the femoral component, our study has shown that use of computer navigation allows more accurate placement of the femoral component even when the surgeons had a significant experience with conventional technique.