Introduction

There have been increased concerns with trunnion fretting and corrosion and adverse local tissue reactions (ALTR) in total hip arthroplasty. We report on 11 catastrophic trunnion failures associated with severe ALTR requiring urgent revision arthroplasty.

Surgical navigation, coupled with preoperative plans, allows surgeons to plan and execute procedures to improve the likelihood of positive outcomes. In real life these navigation systems, which track both the patient and the surgical tools, are not absolutely accurate. Therefore, there is a need to know how much error there may be in the navigation system, so that the surgeon can assess the effects of possible errors in positioning.

The methodology for assessing the accuracy of a surgical navigation system is similar across surgical specialties. We developed a framework for assessing the accuracy of the HipNav system, a computer assisted surgical system used for planning and intra-operative surgical navigation for total hip arthroplasty. This framework can be adapted to other systems and surgical procedures. To assess navigational accuracy, we compared acquired values to a ground-truth model: rigid plastic Sawbones pelvii with mounted fiducials and acetabular implants, whose positions were measured with a coordinate measuring machine. We then identified the individual components of the system that can contribute to overall accuracy, and characterised their contributions to the accuracy of the system. We also measured the end-to-end accuracy of the HipNav system, from initial CT scan through to acetabular cup orientation. This value is of direct importance to the practicing surgeon, and indicates how far off the final measured orientation of the cup may be from its actual location. For the HipNav system, we found that the end-to-end square root of the mean square error was 0.82° in abduction and 0.76° in version.

The accuracy of a surgical navigation system is of vital importance to insure that a preoperative plan is executed properly. To measure the accuracy of a navigation system, accurate models that reflect the relevant anatomy are necessary, and allow true measurement of end-to-end and component accuracy. This example shows how the accuracy of HipNav was assessed, and that the final orientation of the acetabular implant was accurately guided.