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IMAGELESS NAVIGATION IN HIP RESURFACING: THE IMPACT OF SURGICAL VOLUME ON COMPUTER ASSISTED COMPONENT PLACEMENT.

Cincinnati Orthopaedic Research Institute, 9825 Kenwood Road, Suite 200, Cincinnati, Ohio, USA, 45242

Studies suggest that specialty hospitals and high surgical volume decrease adverse outcomes related to hip arthroplasty. Little is known, however, concerning the influence of imageless computer navigation systems on a surgeon’s experience and subsequent placement of implants in the setting of hip resurfacing arthroplasty.

A retrospective review of 71 consecutive hip resurfacing arthroplasties placed with computer assisted navigation during 2006 and 2007 was performed. Forty-seven operative days encompassing the surgeon’s entire experience with hip resurfacing were analysed. Within this single surgeon series, operative time, intraoperative cup inclination and femoral stem/shaft angles, as well as postoperative cup inclination and femoral stem/shaft angles were measured and compared over three discreet, sequential operative time intervals.

Intraoperative cup inclination angles were comparable to postoperative radiographic values as there was no significant difference (p=.059). Computer assisted navigation produced consistent values despite different levels of surgeon experience in the setting of intraoperative cup inclination (42.8°, 43.5°, and 40.1°) and postoperative cup (46.1°, 43.9°, and 42.9°) and femoral stem (147.9°, 146.5°, and 144.0°) radiographic alignment. A statistically significant difference existed between intraoperative femoral stem/shaft angles compared to postoperative radiographs measurements (p<.001), however, all means maintained a valgus orientation compared to the native neck angle. There was a correlation between evolving surgeon experience and intraoperative stem placement (143.5°, 142.1°, and 138.0°, respectively) despite the mean values remaining well clustered (p<.001). Operative times significantly decreased (p<.001) with surgeon experience, showing the largest decrease after the 1^st sequence interval (109.6, 97.8, and 94.8 min, respectively). No femoral notching (0/71) occurred throughout the series.

Computer assisted navigation provides a dependable method of accurate hip resurfacing arthroplasty component positioning as measured by cup inclination, in addition to a reliable technique for valgus stem placement and avoidance of notching. Furthermore, computer navigation allows for consistency and offers a protective effect on component alignment independent of surgeon procedural experience.

Correspondence should be addressed to Mr K Deep, General Secretary CAOS UK, Dept of Orthopaedics, Golden Jubilee National Hospital, Glasgow G81 4HX, Scotland. Email: caosuk{at}gmail.com