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

IntroductionComputer-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.HypothesisUse of cutaneous sensor arrays while recording the HRC is sufficiently reliable for its calculation algorithm to provide measurement accuracy within 5 mm.Materials and methodsA 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.ResultsOn condition that the hip-knee is mobilized in extension, a sensor array attached with an adhesive gives results with comparable accuracy (standard deviation [SD]: 2.89 mm [1.9–4.8]) to the results obtained with a transosseous fixation (SD: 1.2 mm [0.9–1.6]), with no significant inter- or intraobserver variation (0.97 < ICC < 0.99). If the knee was flexed, accuracy was within more than 1 cm, or twice the predetermined limit. Only the adhesive array gave measurements systematically within the limits established with the data spread (8.7%) close to that obtained with a pin (6%).DiscussionAn adhesive array seems to be a reliable alternative to transosseous pins to evaluate HRC and provides a three-dimensional landmark, indispensable to total hip arthroplasty navigation. These preliminary results confirm our hypothesis but should be validated in vivo.Level of evidenceLevel III, comparative prospective in vitro study.