抄録
One hundred eighty-four patients (26 men and 158 women with an average age at operation of 66.7 years) underwent total hip arthroplasty using tapered wedge-shaped cementless stems between 2005 and 2009. The average body mass index of the patients was 23.2 kg/m2 and the primary diagnosis was osteoarthritis in 158 hips (79%). We performed radiographic evaluation (femoral canal shape, bone quality, stem alignment, bone reaction, and stem stability) in order to clarify the indication of tapered wedge-shaped cementless stems for patients with stovepipe canal and type C bone. We developed a novel technique for measuring the three-dimensional implant position, including the precise bone geometry and density data, using pre- and postoperative CT images and a 3D surface registration algorithm. We estimated micromotion (MM) between stem and bone by using this technique in order to analyze the primary stability of the stem. Femoral canal shape (Noble) was stovepipe in 15.5%, normal in 79.5%, and champagne-flute in 5.0%. Bone quality (Dorr) was type A (30.5%), B (62.5%), or C (7.0%). Stem stability was established through bone ingrowth fixation (Engh) for all canal shapes and bone types. The highest value of MM was 236.0 µm and the average was 61.0 µm. The percentage of the area with an MM value higher than 150 µm for the porous-coated surface was 13.6%. In conclusion, good stability of tapered wedge-shaped cementless stems was found in patients with stovepipe canal and type C bone by radiographic and biomechanical analyses.
