Shoji Konda1, Tetsuya Tomita2, Takaharu Yamazaki3, Kosaku Oda4, Mikio Nakajima5, Kunio Nakane6, Kenichi Kono7, Toshitaka Fujito2, Hideki Yoshikawa8, Kazuomi Sugamoto2. 1. Department of Health and Sport Sciences, Osaka university Graduate school of Medicine, 1-17 Machikaneyama, Toyonaka, Osaka 560-0043, Japan. Electronic address: skonda@caos.med.osaka-u.ac.jp. 2. Department of Orthopaedic Biomaterial Science, Osaka university Graduate school of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. 3. Department of Information Systems, Saitama Institute of Technology, 1690 Fusaiji, Fukaya, Saitama 369-0293, Japan. 4. Department of Orthopedic Surgery, Takatsuki Red Cross Hospital, 1-1-1, Abuno, Takatsuki, Osaka 569-1096, Japan. 5. Katsuragi Hospital, 2-33-1, Habucho, Kishiwada, Osaka 596-0825, Japan. 6. Department of Orthopaedic Surgery, Joint Replacement Center, Daiyukai General Hospital, 1-9-9, Sakura, Ichinomiya, Aichi 491-8551, Japan. 7. Department of Orthopaedic Surgery, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. 8. Department of Orthopaedic Surgery, Osaka university Graduate school of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
Abstract
BACKGROUND: Describing three-dimensional joint motion using the finite helical axis has an advantage in understanding unknown coupling motion in prosthetic knee joints. We aimed to examine the differences in the orientations of finite helical axis of normal and anatomically designed cruciate-retaining and posterior-stabilized prosthetic knees after total knee arthroplasty. METHODS: Ten normal, 40 cruciate-retaining prosthetic knees of 33 patients and 19 posterior-stabilized prosthetic knees of 14 patients enabling to flex > 120° were analyzed during a squatting motion with deep knee bending. The motion was recorded by a fluoroscopic imaging system, and the pose of the bone and prostheses were determined by an image registration technique. The finite helical axes were calculated using 30° window. FINDINGS: The finite helical axis in the early flexion phase of the normal knees had a greater inferior inclination (mean - 19.0° (SD 7.2°)) than those of the cruciate-retaining (mean - 1.7 (SD 5.0°)) and posterior-stabilized (mean - 2.9° (SD 5.5°)) prosthetic knees (p < 0.001), and became almost horizontal and constant in the mid to deep flexion phases. In contrast, the cruciate-retaining and posterior-stabilized prosthetic knees demonstrated slightly inclined and almost constant vertical angles throughout the all phases. INTERPRETATION: These results demonstrate that, in the normal knee, a clear coupling motion occurs during the early flexion phase. For the cruciate-retaining and posterior-stabilized prosthetic knees, an unclear coupling motion exists during all phases. These results suggest that the physiological motion is not possible to reproduce using shape-guided motion only even in an anatomically designed prosthetic knee.
BACKGROUND: Describing three-dimensional joint motion using the finite helical axis has an advantage in understanding unknown coupling motion in prosthetic knee joints. We aimed to examine the differences in the orientations of finite helical axis of normal and anatomically designed cruciate-retaining and posterior-stabilized prosthetic knees after total knee arthroplasty. METHODS: Ten normal, 40 cruciate-retaining prosthetic knees of 33 patients and 19 posterior-stabilized prosthetic knees of 14 patients enabling to flex > 120° were analyzed during a squatting motion with deep knee bending. The motion was recorded by a fluoroscopic imaging system, and the pose of the bone and prostheses were determined by an image registration technique. The finite helical axes were calculated using 30° window. FINDINGS: The finite helical axis in the early flexion phase of the normal knees had a greater inferior inclination (mean - 19.0° (SD 7.2°)) than those of the cruciate-retaining (mean - 1.7 (SD 5.0°)) and posterior-stabilized (mean - 2.9° (SD 5.5°)) prosthetic knees (p < 0.001), and became almost horizontal and constant in the mid to deep flexion phases. In contrast, the cruciate-retaining and posterior-stabilized prosthetic knees demonstrated slightly inclined and almost constant vertical angles throughout the all phases. INTERPRETATION: These results demonstrate that, in the normal knee, a clear coupling motion occurs during the early flexion phase. For the cruciate-retaining and posterior-stabilized prosthetic knees, an unclear coupling motion exists during all phases. These results suggest that the physiological motion is not possible to reproduce using shape-guided motion only even in an anatomically designed prosthetic knee.