Is determination of the hip rotation center during computer-assisted surgery influenced by the pinless femoral sensor attachment method? An in vitro preliminary study comparing osseous pin fixation.

INTRODUCTION: Computer-assisted surgery improves the positioning of hip prostheses but requires use of transosseous pins requiring a complementary approach exposing the patient to rare but at times serious complications. The use of sensor arrays attached to the skin could advantageously replace pins provided that comparable results are obtained, but their validity has not yet been assessed. We conducted a prospective in vitro study to: measure the possible error of a cutaneous versus transosseous fixation to determine the hip rotation center (HRC) position and determine the inter- and intraobserver reproducibility of the cutaneous versus the transosseous fixation. HYPOTHESIS: Use of cutaneous sensor arrays while recording the HRC is sufficiently reliable for its calculation algorithm to provide measurement accuracy within 5mm. MATERIALS AND METHODS: A rigid array attached with either a silicone strap or an adhesive were compared to a transosseous array. Four series of 96 HRC measurements were collected by four operators on two cadavers, half with an array attached with a strap and half with an adhesive. The results were compared to those obtained by a sensor attached with transosseous pins. RESULTS: On condition that the hip-knee is mobilized in extension, a sensor array attached with an adhesive gives results with comparable accuracy (standard deviation [SD]: 2.89mm [1.9-4.8]) to the results obtained with a transosseous fixation (SD: 1.2mm [0.9-1.6]), with no significant inter- or intraobserver variation (0.97