Xiao-Hong Wang1,2, Da-Yong Song3, Xiang Dong4, Toru Suguro5, Cheng-Kung Cheng6,7. 1. School of Biological Science and Medical Engineering, Beihang University, Beijing, 100083, China. 2. Naton Institute of Medical Technology, Beijing, 100095, China. 3. Beijing Medical Implant Engineering Research Center, Beijing Naton Technology Group Co. LTD, Beijing, 100082, China. 4. Beijing Engineering Laboratory of Functional Medical Materials and Devices, Beijing Naton Technology Group Co. LTD, Beijing, 100082, China. 5. Japan Research Institute of Artificial Joint, Research Institute of Rheumatology Medical Treatment, Tokyo, 104-0032, Japan. 6. School of Biological Science and Medical Engineering, Beihang University, Beijing, 100083, China. ckcheng2009@gmail.com. 7. Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing, 100191, China. ckcheng2009@gmail.com.
Abstract
PURPOSE: Single radius knee implants were introduced to reduce the level of paradoxical anterior femoral translation (AFT) during mid-flexion after total knee arthroplasty. Findings from clinical and experiment studies are inconsistent, which may be due to the different loading conditions and articular conformities of the knee implants studied. The aim of this study is to analyze how variations in these two factors affect the mid-flexion stability of a single radius knee prosthesis. METHODS: Six daily activities (walking, stair ascent, stair descent, sit-to-stand, pivot turn and crossover turn), and three articular conformity ratios (low, moderate and high) were considered. The resulting AFTs from the 18 finite element models were analyzed. RESULTS: For low conformity knees, the worst case activity (the greatest AFT) was sit-to-stand with an AFT of 6.2 mm, while for the moderate conformity the worst case was crossover turn and pivot turn. For high conformity, all activities produced a relatively small AFT ranging from 0 mm to 1.8 mm, which more closely resembles natural knee motion. In addition, no AFT was recorded during stair ascent for all three conformities (low, moderate, high). CONCLUSIONS: This study demonstrated that the amount of AFT is highly dependent on the activity being undertaken and the articular conformity of the knee prosthesis, and the worst case activity depends on the knee conformity. The clinical relevance of this study is that it offers valuable information towards the design of improved knee prostheses and selection of knee implants for clinical use. LEVEL OF EVIDENCE: II.
PURPOSE: Single radius knee implants were introduced to reduce the level of paradoxical anterior femoral translation (AFT) during mid-flexion after total knee arthroplasty. Findings from clinical and experiment studies are inconsistent, which may be due to the different loading conditions and articular conformities of the knee implants studied. The aim of this study is to analyze how variations in these two factors affect the mid-flexion stability of a single radius knee prosthesis. METHODS: Six daily activities (walking, stair ascent, stair descent, sit-to-stand, pivot turn and crossover turn), and three articular conformity ratios (low, moderate and high) were considered. The resulting AFTs from the 18 finite element models were analyzed. RESULTS: For low conformity knees, the worst case activity (the greatest AFT) was sit-to-stand with an AFT of 6.2 mm, while for the moderate conformity the worst case was crossover turn and pivot turn. For high conformity, all activities produced a relatively small AFT ranging from 0 mm to 1.8 mm, which more closely resembles natural knee motion. In addition, no AFT was recorded during stair ascent for all three conformities (low, moderate, high). CONCLUSIONS: This study demonstrated that the amount of AFT is highly dependent on the activity being undertaken and the articular conformity of the knee prosthesis, and the worst case activity depends on the knee conformity. The clinical relevance of this study is that it offers valuable information towards the design of improved knee prostheses and selection of knee implants for clinical use. LEVEL OF EVIDENCE: II.