VERIFICATION STUDIES OF CAOS IN HIP ARTHROPLASTY

Abstract

Introduction: With the increasing use of CAOS techniques in Orthopaedic Surgery it is important to be aware of verification studies and sources of error that can occur. Computer assisted navigation systems should be tested with a known true standard such as a phantom model and then verified with cadaver studies before clinical trials are instituted. Errors can occur.

Materials and Methods: A major focus for hip arthroplasty navigation has been on acetabular cup anteversion and inclination. Non CT navigation systems rely on an anterior pelvic plane, which is selected by the surgeon. This study looked at repeated measurements of a surgeon’s ability to manually pick the pubic symphysis and the ASIS and compared this to the same points selected fluoroscopically. A navigated acetabular cup was performed aiming for abduction of 45° and anteversion of 20°. The software model was then manipulated to transpose the different registrations to see what compound effect the anterior pelvic plane error would have.

Results: Significant intra and inter observation error was recorded for registration by palpation compared to points registered by the fluoroscopic method. An error of up to 9.6° cup inclination and 11.2 ° cup anteversion could be introduced with a palpation method.

Conclusion: This cadaver study indicates that with hip arthroplasty, registration from a fluoroscopic image was more accurate with a respect to determining the anterior pelvic plane when compared to direct palpation. Like all surgery done with computer navigation, registration requires an accurate determination of the points that the software needs for calculation. This must always be borne in mind when evaluating methods for CAOS.