THE ACCURACY OF A COMPUTER-ASSISTED NAVIGATION SYSTEM FOR RESURFACING HIP ARTHROPLASTY: AN IN-VITRO STUDY

Background Correct positioning of the femoral component in resurfacing hip arthroplasty (RHA) is an important factor in successful long-term outcomes. The purpose of computer-assisted navigation (CAS) in resurfacing is to insert the femoral neck guide wire with greater accuracy and to help size the femoral component, thus reducing the risk of notching at the head and neck junction. Several recent studies reported satisfactory precision and accuracy of CAS. However, there is little evidence that CAS is useful in the presence of anatomical deformities of the proximal femur, which is frequently observed in young patients with secondary degenerative joint disease. Aim The purpose of this in vitro study was to determine the accuracy of an image-free RHA navigation system in the presence of angular deformity of the neck, pistol grip deformity of the head and neck junction and slipped upper femoral epiphysis deformity. Methods An artificial phantom leg was used. Implant-shaft angles for the guide wire of the femoral component reamer were calculated, in frontal and lateral planes, with the computer navigation system and an electronic caliper combined with micro-CT. Results With both normal anatomy and angular deformity we found close agreement between the CAS system and our measurement system. There was a consistent disagreement on both planes for the pistol grip deformity. In the presence of the slipped upper femoral epiphysis deformity, close agreement was found only on the frontal plane but calculation of the femoral head size was inaccurate. Conclusion This is the first study designed to assess the accuracy of a femoral navigation system for RHA in the presence of anatomical deformity of the proximal femoral head and neck segment. Our data suggests CAS technology should not be used to expand the range of utilisation of resurfacing surgery to these cases but rather to improve the surgical outcome in those with suitable anatomy.