Toshihiro Sera1, Yuya Iwai2, Takaharu Yamazaki3, Tetsuya Tomita4, Hideki Yoshikawa4, Hisahi Naito2, Takeshi Matsumoto2, Masao Tanaka2,5. 1. Department of Mechanical Engineering, Kyushu University, Fukuoka, Japan. 2. Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Osaka, Japan. 3. Department of Information Systems, Saitama Institute of Technology, Saitama, Japan. 4. Orthopaedic Surgery, Graduate School of Medicine, Osaka University, Osaka, Japan. 5. Global Center for Medical Engineering and Informatics, Osaka University, Osaka, Japan.
Abstract
OBJECTIVE: The longevity of a knee prosthesis is influenced by the wear of the tibial insert due to its posture and movement. In this study, we assumed that the strain on the tibial insert is one of the main reasons for its wear and investigated the influence of the knee varus-valgus angles on the mechanical stress of the tibial insert. METHODS: Knee prosthesis motion was simulated using a knee motion simulator based on a parallel-link six degrees-of-freedom actuator and the principal strain and pressure distribution of the tibial insert were measured. In particular, the early stance phase obtained from in vivo X-ray images was examined because the knee is applied to the largest load during extension/flexion movement. The knee varus-valgus angles were 0° (neutral alignment), 3°, and 5° malalignment. RESULTS: Under a neutral orientation, the pressure was higher at the middle and posterior condyles. The first and second principal strains were larger at the high and low pressure areas, respectively. Even for a 3° malalignment, the load was concentrated at one condyle and the positive first principal strain increased dramatically at the high pressure area. The negative second principal strain was large at the low pressure area on the other condyle. The maximum equivalent strain was 1.3-2.1 times larger at the high pressure area. For a 5° malalignment, the maximum equivalent strain increased slightly. CONCLUSION: These strain and pressure measurements can provide the mechanical stress of the tibial insert in detail for determining the longevity of an artificial knee joint.
OBJECTIVE: The longevity of a knee prosthesis is influenced by the wear of the tibial insert due to its posture and movement. In this study, we assumed that the strain on the tibial insert is one of the main reasons for its wear and investigated the influence of the knee varus-valgus angles on the mechanical stress of the tibial insert. METHODS: Knee prosthesis motion was simulated using a knee motion simulator based on a parallel-link six degrees-of-freedom actuator and the principal strain and pressure distribution of the tibial insert were measured. In particular, the early stance phase obtained from in vivo X-ray images was examined because the knee is applied to the largest load during extension/flexion movement. The knee varus-valgus angles were 0° (neutral alignment), 3°, and 5° malalignment. RESULTS: Under a neutral orientation, the pressure was higher at the middle and posterior condyles. The first and second principal strains were larger at the high and low pressure areas, respectively. Even for a 3° malalignment, the load was concentrated at one condyle and the positive first principal strain increased dramatically at the high pressure area. The negative second principal strain was large at the low pressure area on the other condyle. The maximum equivalent strain was 1.3-2.1 times larger at the high pressure area. For a 5° malalignment, the maximum equivalent strain increased slightly. CONCLUSION: These strain and pressure measurements can provide the mechanical stress of the tibial insert in detail for determining the longevity of an artificial knee joint.
Keywords:
Knee motion simulator; Principal strain; Total knee arthroplasty; Varus-valgus; Wear
Authors: Michael E Berend; Merrill A Ritter; John B Meding; Philip M Faris; E Michael Keating; Ryan Redelman; Gregory W Faris; Kenneth E Davis Journal: Clin Orthop Relat Res Date: 2004-11 Impact factor: 4.176