James R. Romanowski, MD¹ and Michael L. Swank, MD²

¹ Department of Orthopaedic Surgery, University of Cincinnati, 224 Leather Leaf Lane, Lebanon, OH 45036
² Cincinnati Orthopaedic Research Institute, 9825 Kenwood Road, Suite 200, Cincinnati, OH 45242

Background: Studies suggest that hip arthroplasty procedures performed in specialty hospitals or by physicians in practices with a high surgical volume are associated with a decreased rate of adverse outcomes related to component malpositioning. Little is known, however, about the influence of imageless computer navigation systems on the procedural experience of the surgeon and the subsequent alignment of implants in the setting of hip resurfacing arthroplasty.

Methods: Seventy-one consecutive hip resurfacing arthroplasties in which the components were placed with use of computer-assisted navigation were reviewed retrospectively. Intraoperative femoral and acetabular component parameters were compared with postoperative radiographic alignment values. Within this single surgeon series, operative time, intraoperative cup inclination and femoral stem-shaft angles, and postoperative cup inclination and femoral stem-shaft angles were measured and compared over the course of three discrete, sequential operative time periods. Patient demographic data and surgical parameters, including blood loss, surgical approach, and anesthesia time, were recorded.

Results: No significant difference was seen between the intraoperative and postoperative cup inclination angles. A significant difference was noted between the intraoperative and postoperative femoral stem-shaft angles; however, the mean angles in all groups had a valgus orientation when compared with the mean native neck angles. Over three sequential operative time periods, computer-assisted navigation produced consistent values with regard to intraoperative cup inclination (43°, 44°, and 40°) and postoperative radiographic alignment of the cup (46°, 44°, and 43°) and femoral stem (148°, 147°, and 144°), despite different levels of surgeon experience. Operative times significantly decreased with surgeon experience, showing the largest decrease after the first sequence interval (110, ninety-eight, and ninety-five minutes, respectively). There was a significant difference with evolving surgeon experience concerning intraoperative stem placement (144°, 142°, and 138°, respectively) despite the mean values remaining well-clustered. No femoral notching occurred throughout the series.

Conclusions: Computer-assisted navigation is a dependable and accurate method of positioning hip resurfacing components during arthroplasty, as measured by cup inclination, and a reliable technique for valgus stem placement and avoidance of notching. Furthermore, computer navigation allows for consistency of component alignment independent of procedural experience.