Introduction

We developed original KKS non-cement THA system and used clinically over 10 years. KKS means Keio Kyocera Series. This system was developed co-ordinating with Keio-University and Kyocera Company in Japan. Our concept was to make original THA system suitable for Japanese people. Osteoarthritis of the hip in Japanese people caused mainly from developmental dysplasia of the hip. So the shape of femoral medullary canal is characteristic compared with foreign patients. We analyzed the femoral medullary canal shape in typical Japanese osteoarthritis 50 cases of the hip by the use of CT scan. From the results of these analyses, we determined the optimal shape of KKS non-cement stem for Japanese patients. It has double tapered shape in distal stem shaft. Proximal taper angle of the stem is 4 degree, and distal one is 3 degree. The proximal part of stem has characteristic notch in anterior and posterior and lateral surface to tolerate rotational stability.

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.

We have used CT-based total hip navigation system from 2003, to set the acetabular socket in optimal position. At first, we had used CT-based land-mark matching system. It needs matching procedure during surgery, touching paired points in surgical exposure. From 2006, we started to use new navigation system, called CT-based fluoroscopy-matching system, which was developed by BrainLAB Company (Vector-vision 2.7.1., 3.5.1.). For this new system, pre-surgical image matching procedure is need. Fluoroscopic images with 2 different directions must be taken in operation room. Then fluoroscopic images and CT reconstructive images were matched in computer with special program. Matching procedure was done before surgical incision. We compared the advantage of these two systems about technical problem, radiation exposure, time need for procedure, and accuracy. And then we discussed how to use these two different systems for THA patients.

Accuracy was compared for 241 THA patients using these navigation systems. 152 cases were with CT-based land-mark matching system and 89 patients with CT-based fluoroscopy matching system. Final verification angle of acetabular socket setting in navigation during surgery was recorded for each case. The operative angle, which is referred from Murray, is used to show the socket setting angle (inclination and anteversion) in these navigation systems. Post-operative CT scan was taken to evaluate the actual socket setting angle. The values between verification angle during surgery and post-operative CT measured angle were calculated and compared statistically.

Results were followed. New CT-based fluoroscopy matching method (F method): Average setting angle (operative angle) of socket in these 89 cases were 42.9 +/− 5.1 degree in inclination angle, and 28.5 +/− 7.9 degree in anteversion angle. The absolute difference in 89 cases between final verification angle and post-operative CT measurement angle was 2.9 degree (on average) +/− 2.5 degree in inclination angle, and 2.8 degree (on average) +/− 2.6 degree in anteversion angle. Conventional CT-based land-mark matching method (L method): The absolute difference in 152 cases between final verification angle and post-operative CT measurement angle was 4.2 degree (on average) +/− 3.2 degree in inclination angle, and 4.4 degree (on average), +/− 3.7 degree in anteversion angle. Absolute differences of setting angle in fluoroscopy matching groups showed statistically low compared with land-mark matching groups (P<0.01).

Technical problems: L method is difficult to learn actual procedure. F method is easy to learn procedure. Image matching was done automatically by computer program. Radiation exposure during surgery: L method needs no additional radiation. F method needs radiation to get 2 fluoroscopic images. Total amount time need for navigation: L method needs extra 10 minutes during surgery in case of skilled-doctor. F method needs extra 20 minutes before starting surgery in case of all kind doctors. The accuracy of acetabular socket setting: Absolute errors in socket setting with theses two systems were within 5 degree together on average. These results showed the usefulness of both systems. Compared the accuracy between these 2 systems, F methods showed high accuracy. The accuracy of F methods is always high. It has no influence with deformity around hip joint, because fluoroscopic image matching was done with lower part of pubic bone, especially around symphysis pubis.

For ordinary THA cases with skilled-doctor, CT-based land-mark matching system is useful, because this system is very convenient and needs only extra 10 minutes during surgery. For severe deformed cases with all kind doctors, CT-based fluoroscopy matching system is useful, because this system showed high accuracy even for severe deformed cases. Before surgical incision, fluoroscopic matching procedure has finished. This system needs no extra time after surgery starts.