Abstract
Introduction
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.
Material
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.
Results
The absolute difference in L method (273 cases) was on average 3.9 +/− 3.1 degree in inclination, and 4.0 +/− 3.4 degree in anteversion. The absolute difference in F method (204 cases) was on average 2.8 +/− 2.3 degree in inclination, and 2.9 degree +/− 2.6 in anteversion. The values in F method groups showed high accuracy (P<0.01).
Discussion
Accurate socket setting in THA is essential for preventing dislocation and ensuring long term usage of prosthesis. Absolute errors in socket setting with theses two navigation systems were within 4 degree on average. These results showed the usefulness of both navigation systems. F method is new technology using image matching procedure of fluoroscopy and CT-scan doing on computer (Fig. 3). F method is easy to learn actual procedure and showed high accuracy. L method is conventional procedure and needs skill to use correctly. But it needs short additional time and so it is convenient for skilled-doctor.
