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Objective To study the effects of prosthetic alignment on internal contact mechanical characteristics of intact knee joint for transfemoral amputees. Methods The gait experiment of transfemoral amputees was performed under different alignment conditions, and the differences of lower limb motion and ground reaction force (GRF) were analyzed and compared with those of the non-amputees. The three-dimensional （30） finite element model of knee joint was build and used to analyze the effect of alignments of socket adduction and abduction on internal contact mechanical characteristics between femur cartilage, tibia cartilage and meniscus. Results For knee joint of the non-amputees, contact force was mainly concentrated on the medial sides at the moment of the first GRF peak, while contact force was mainly concentrated on the lateral sides at the moment of the second GRF peak. However, for intact knee joint of the transfemoral amputees, contact force was mainly concentrated on the medial side at the moment of two GRF peaks. The stress of the medial meniscus, contact force and contact area between the medial meniscus and cartilage all obviously increased under the alignment of 6° socket adduction. Conclusions Compared with non-amputees, the incidence of knee osteoarthritis (OA) in amputees was higher, which was related to the long-term overload of the medial knee joint. The alignment of socket adduction may increase the risk of knee OA in the intact side of transfemoral amputees. In clinic, excessive adduction of the socket should be avoided during prosthetic alignment.
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Objective To investigate the biomechanical effects of interbody cage height on cervical spine during anterior cervical discectomy and fusion (ACDF) surgery,so as to provide references for selection of interbody cage.Metheds The finite element model of normal cervical spine (C2-7) was built and validated,and the cages with different height (5,6,7,8 mm) were implanted into C5-6 disc (cage 5,6,7,8 model).All the models were loaded with pure moment of 1.5 N · m to produce flexion,extension,lateral bending and axial rotation motions on cervical spine,and the effects of cage height on range of motion (ROM),facet joint stress,intervertebral pressure in cervical spine were investigated.Results The intervertebral angle at the fusion segment increased by 0.68° with per 1 mm-increase in height.The ROM in C5-6 after cage implantation was smaller than 0.44°.The influence of cage height on ROM in C4-5 was greater than that in C6-7,and the changes of ROM in non-fusion segments were smaller than 7.3％.The cage height variation had a smaller impact on the facet joint stress and intervertebral pressure.The stresses in the capsular ligament,cage and screw-plate system increased gradually with the increase of cage height,and the stresses in cage 6,7,8 models were much higher than those in cage 5 model.Conclusions For patients who need implanting fusion cage,the cage height should be 0-1 mm greater than the original intervertebral space height.
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We observed the effect of vibration parameters on lumbar spine under different vibration conditions using finite element analysis method in our laboratory. In this study, the CT-images of L1-L5 segments were obtained. All images were used to develop 3D geometrical model using the Mimics10. 01 (Materialise, Belgium). Then it was modified using Geomagic Studio12. 0 (Raindrop Geomagic Inc. USA). Finite element (FE) mesh model was generated by Hypermesh11. 0 (Altair Engineering, Inc. USA) and Abaqus. Abaqus was used to calculate the stress distribution of L1-L5 under different vibration conditions. It was found that in a vibration cycle, tensile stress was occurred on lumbar vertebra mainly. Stress distributed evenly and stress concentration occurred on the left rear side of the upper endplate. The stress had no obvious changes under different frequencies, but the stress was higher when amplitude was greater. In conclusion, frequency and amplitude parameters have little effect on the stress distribution in vertebra. The stress magnitude is positively correlated with the amplitude.
Subject(s)
Humans , Biomechanical Phenomena , Finite Element Analysis , Lumbar Vertebrae , Physiology , VibrationABSTRACT
This study was aimed to estimate the effect of different ProDisc-C arthroplasty designs after it was implanted to C5-C6 cervicalspine. Finite element (FE) model of intact C5-C6 segments including the vertebrae and disc was developed and validated. Ball-and-socket artificial disc prosthesis model (ProDisc-C, Synthes) was implanted into the validated FE model and the curvature of the ProDisc-C prosthesis was varied. All models were loaded with compressed force 74 N and the pure moment of 1.8 Nm along flexion-extension and bilateral bending and axial torsion separately. The results indicated that the variation in the curvature of ball and socket configuration would influence the range of motion in flexion/extension, while there were not apparently differences under other conditions of loads. The method increasing the curvature will solve the stress concentration of the polyethylene, but it will also bring adverse outcomes, such as facet joint force increasing and ligament tension increasing. Therefore, the design of artificial discs should be considered comprehensively to reserve the range of motion as well as to avoid the adverse problems, so as not to affect the long-term clinical results.