Abstract
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.
Objectives
We evaluated long terms results (over 10 years) of KKS original stem mainly radio graphically and estimate the usefulness.
Methods
We started to use porous HA coated KKS stem from 1995. From 1995 to 1998 this stem was applied for 73 cases of non-cement THA in Keio-University. Excluding 2 cases of infection and stem breakage, 55 of 71 cases could be followed over 10 years (follow-up rate: 75%). In these 55 cases, average age at THA operation was 54 (24–64) years old and mean follow-up time was 11.2 (10–13) years. Radiographic findings in 55 cases at follow-up time were evaluated, concerning about following points: stem sinking, loosening, spots-welds, calcar resorption, and osteolysis on femoral side.
Results
No sinking and no loosening of the stem were seen. Calar resorption was seen in 22 cases: 40%. Spot-welds was seen in almost cases on 51/55:92%. Osteolysis was seen in 9 cases, zone1;1 case, zone 7;8 cases. Clinical results were excellent as radiographic results.
Conclusions
The aim to develop this system is to make optimal shape stem suitable for Japanese patients. Optimal fitting in the femoral medullary canal by KKS stem was confirmed on X-P. High occurrence rate of spot-welds showed strong stability to bone. On X-ray evaluation, no stem sinking and no loosening were found at over 10 years after operation. It proved the enough biological fixation to bone for a long time. But osteolysis occurred in 9 cases. This may come from the use of conventional polyethylene socket. Now cross-linked polyethylene socket is used and the wear of socket is expected to reduce. Off course longer follow-up of KKS system is needed. But the evaluation of KKS stem at 10 years follow-up indicated enough usefulness.
