We have used CT-based navigation system for THA from 2004 (Fig, 1). The purpose is to set acetabular socket in optimal position. We have used two different matching methods in these navigation THA surgeries. The old one is Land-mark matching method (L-method), using conventional paired point matching procedure during surgery. The new one is CT-based fluoroscopy-matching system (F-method), that is new technology of image matching procedure before starting surgery (Fig. 2). We compared the accuracy of socket setting angle with these two systems and discuss the usefulness of navigation system. Materials were 477 THA patients using these navigation systems. 273 cases were with L method and 204 patients were with F method. The values between verification angle by navigation system during surgery and post-operative measured angle (by X-ray or CT scan) were calculated and compared.Introduction
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