Abstract
Metal on Metal hip resurfacing (MoM HR) can be an effective operation for the young arthritic hip population. However, errors in cup orientation have been associated with increased wear, circulating blood metal ions, and soft tissue abnormalities that can lead to premature failure of the bearing surface and subsequent revision surgery. While image free computer guidance has been shown to increase surgical accuracy in total hip arthroplasty, the role of image based technology in MoM HR is unclear. In this study, we compared the accuracy of cup orientation in MoM HR performed by either freehand technique or CT based navigation.
Seventy five patients (81 hips) underwent either freehand (n=42) or navigation (n=39) surgery, both requiring a three dimensional (3D) CT surgical plan. Surgery was conducted by hip specialists blind to the method of cup implantation until the operation. Deviation in inclination and version from the planned orientation, as well as, number of cups within a 10° safe zone and 5° optimal zone of the target position was calculated using post operative 3D CT analysis.
Error in inclination was significantly reduced with navigation compared to freehand technique (4° vs 6°, p=0.02). We could not detect a difference between the two groups for version error (5° vs 7°, p=0.06). There was a significantly greater number of hips within a 10° (87% vs 67%, p=0.04) and 5° (50% vs 20%, p=0.06) safe zone when navigated.
Image based navigation can substantially improve accuracy in cup orientation. The results of our freehand group appear better than historic controls, suggesting the use of a 3D plan may help to reduce technical error and improve the learning curve in this technically demanding procedure. We advocate the use of image based navigation in MoM hip resurfacing arthroplasty.
