ACCURACY OF A COMPUTER-ASSISTED NAVIGATION SYSTEM FOR RESURFACING HIP ARTHROPLASTY

Abstract

Implant malposition is one of the most common causes of failure in resurfacing arthroplasty of the hip (RAH). Recent advances in computer technology have made available navigation systems for RAH and other orthopaedic procedures. The purpose of our study was:

1. to develop a method to assess the accuracy of an image-free RAH navigation system;

2. to assess its accuracy in a leg with normal anatomy and with deformity of the proximal femur.

We used the Ci-CAS RAH navigation system (DePuy - BrainLab). To facilitate measurements, an artificial leg (phantom) was constructed from machined aluminium with simulated hip and knee joints. The hip and knee articulating surfaces were synthetic bone material (Sawbones – Pacific Laboratories). An additional joint located at the trochanteric region allowed deformation in varus/valgus and ante/retroversion of the head/neck segment. Using a highly accurate digital calliper unit (FaroARM Technologies, USA) to precisely measure co-ordinates with pre-machined points on the phantom, a software program was developed to convert these local co-ordinates into a determination of actual anatomy and leg alignment. This technique was verified using repeated measurement with variable co-ordinates, giving accuracy to within 0.05 of a degree.

Simulated procedures were performed with both normal and abnormal anatomy of the proximal femur. At specific points in the procedure, information was compared between the FaroARM digital measurements and the Ci-CAS system. Repeated serial measurements were undertaken. In the setting of normal alignment, accuracy to within 0.5 degrees was demonstrated. In the setting of abnormal alignment (varus/valgus and ante/retroversion) of the proximal femur, accuracy to within 2 degrees was demonstrated.

To our knowledge, this is the first study to assess accuracy of a RAH navigation system. The study demonstrates a satisfactory level of accuracy for the Ci-CAS in both normal and abnormal anatomical settings. Currently, no international standard or methodology exists against which these results can be compared. In the near future, introduction of new navigation technologies will make crucial the development of international standards for pre-clinical validation of computer-assisted navigation systems. The present study is a first attempt to address this issue.