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Objective To perform finite element analysis on a type of newly designed total knee prosthesis,and investigate the influence from changing twist angle of the lateral condyle surface on mechanical environment of the knee joint.Metheds Based on CT measurement data from a volunteer,3 artificial knee prostheses with the same medial condyle were established.In Model 1,the twist angle of lateral condyle surface was 0°,while 10° and 20° in Model 2 and Model 3,respectively.The prosthesis models were imported into finite element software and applied with gait cycle data to simulate the motion of knee prosthesis during the gait cycle.The simulated stress results in the knee joint were then compared with the calculated results,which were obtained from theoretical formula of contact mechanics.Results The maximum stress of 3 models appeared at 13％ of the gait cycle,when the axial force (2.6 kN) was also the maximum.The maximum stresses of medial and lateral condyle in Model 1,Model 2 and Model 3 were 35.5 and 30.6 MPa,38.4 and 32.6 MPa,38.3 and 43.1 MPa,respectively.The stress curves of Model 2 and Model 3 during the gait cycle were relatively smooth compared with those of Model 1.The simulated stress trend was basically similar to the theoretical calculation,except at a few moments in the gait cycle.Conclusions The mechanical environment of the total knee prosthesis can be improved by twist angle of the lateral condyle surface.This newly designed prosthesis can preserve implants from abrupt change of the stress during the gait cycle and prolong the service life of prostheses.
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Objective To perform finite element analysis on a type of newly designed total knee prosthesis, and investigate the influence from changing twist angle of the lateral condyle surface on mechanical environment of the knee joint. Methods Based on CT measurement data from a volunteer, 3 artificial knee prostheses with the same medial condyle were established. In Model 1, the twist angle of lateral condyle surface was 0°, while 10° and 20° in Model 2 and Model 3, respectively. The prosthesis models were imported into finite element software and applied with gait cycle data to simulate the motion of knee prosthesis during the gait cycle. The simulated stress results in the knee joint were then compared with the calculated results, which were obtained from theoretical formula of contact mechanics. Results The maximum stress of 3 models appeared at 13% of the gait cycle, when the axial force (2.6 kN) was also the maximum. The maximum stresses of medial and lateral condyle in Model 1, Model 2 and Model 3 were 35.5 and 30.6 MPa, 38.4 and 32.6 MPa, 38.3 and 43.1 MPa, respectively. The stress curves of Model 2 and Model 3 during the gait cycle were relatively smooth compared with those of Model 1. The simulated stress trend was basically similar to the theoretical calculation, except at a few moments in the gait cycle. Conclusions The mechanical environment of the total knee prosthesis can be improved by twist angle of the lateral condyle surface. This newly designed prosthesis can preserve implants from abrupt change of the stress during the gait cycle and prolong the service life of prostheses.
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Objective To propose a personalized design of anatomic ankle prosthesis that can avoid and reduce the high failure rate and risk of ankle prosthesis in clinic. Methods The 3D finite element non-linear model of normal human ankle system was established and verified. The anatomic ankle prosthesis was then designed to simulate total ankle replacement, and the 3D finite element model with both the prosthesis and ankle system was established. The biomechanical characteristics of this prosthesis were calculated and analyzed after gait loads were applied. Results For the normal ankle system, the maximum plantar contact stress was 214.6 kPa and the maximum Von Mises stress of foot bone was 8.96 MPa. The reliability of the normal ankle system model was verified by comparing the simulated results with those reported by literature. After the prosthesis implantation, the simulated maximum Von Mises stresses of talus prosthesis, tibial UHMWPE liner, tibial prosthesis were 23.88, 19.24 and 73.01 MPa, respectively. The stress of the ankle prosthesis increased drastically compared with that of normal ankle system. Conclusions The comparison results by finite element analysis examine the feasibility of the personalized ankle prosthesis, and provide references for optimization of prosthesis design and its clinical application.
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STUDY DESIGN: This study is a prospective, clinical study assessing the efficacy of selective decompression of the level responsible in a two-level stenosis in accordance with the neurological findings defined by the gait load test with a treadmill. PURPOSE: To clarify the clinical features of multilevel lumbar spinal stenosis (LSS) regarding the neurological level responsible for the symptoms, neurogenic claudication, and outcomes of selective decompression. OVERVIEW OF LITERATURE: Most spine surgeons have reported that multilevel compression of the cauda equina induces a more severe impairment of the nerve function than a single-level compression. However, the clinical effects of multilevel LSS on the cauda equine and nerve roots are unknown. METHODS: A total of 21 patients with lumbar spinal canal stenosis due to spondylosis and degenerative spondylolisthesis were selected. The level responsible for the symptoms in the two-level stenosis was determined from the neurological findings on the gait load test and functional diagnosis based on a selective nerve root block. All patients underwent a prospective, selective decompression at the level neurologically responsible only. The average follow-up period was 2.6 years (range, 1 to 6 years). The postsurgical outcome was defined using the Visual Analogue Scale (VAS) at the post-gait load test, 2 weeks after surgery, 3 months after surgery and at the last follow up. RESULTS: Before surgery, the mean threshold distance and mean walking tolerance was 34.3 m and 113 m, respectively. All patients had neurogenic claudication and 19 of the patients had cauda equina syndrome, including hypesthesia in 11 cases, muscle weakness in 5 cases and radicular pain in 7 cases. Selective nerve blocks to determine the level responsible for the lumbosacral symptoms in 2 cases revealed a mean VAS score of 7.1, 2.61, 3.04, and 3.47 at the post-gait load test, 2 weeks after surgery, 3 months after surgery and at the last follow up, respectively. All subjects underwent surgery. After the operation, neurogenic claudication with or without cauda equna syndrome subsided in all patients. CONCLUSIONS: The gait load test allows an objective and quantitative evaluation of the gait characteristics of patients with lumbar canal stenosis and is useful for determining the appropriate level for surgical treatment.