RÉSUMÉ
Objective To investigate the changes of plantar pressure distributions in children with the unilateral developmental dysplasia of the hip (DDH) who underwent the Pemberton’s pericapsular osteotomy (PPO) at early age, so as to provide valuable references for clinical therapy and rehabilitation of such patients. Methods Eighteen child patients who underwent PPO before 4 year old were selected as the PPO group, while 18 healthy children at the same age with normal feet were selected as the control group. Footscan system was used to measure the plantar pressure of these subjects during walking. The parameters, i.e. contact area percentage of the total foot contact area (CA%), pressure-time integral (PTI) and contact time percentage of the stance time (CT%) in both PPO group and control group were compared to evaluate changes of the plantar pressures during walking. Results Compared with the sound limb in control group and the unaffected limb in PPO group, the affected limb in PPO group showed higher PTI in the 2nd to 5th toe zone and lower PTI in the medial heel zone. The affected limb in PPO group had a higher CA% in the 4th and 5th metatarsals than the unaffected limb in PPO group and the sound limb in control group, and a lower CA% in the 1st and 2nd metatarsals than the unaffected limb. Compared with the unaffected limb in PPO group and the sound limb in control group, CT% of the affected limb in PPO group increased in the forefoot push-off phase and decreased in the initial contact phase, and the total contact time of the affected limb was shorter than that of the unaffected limb in PPO group and the sound limb in control group. Conclusions There exist residual plantar pressure deviations during walking in DDH patients following PPO at early age, thus a longer period of intensive rehabilitation may be required to change the residual abnormality.
RÉSUMÉ
Objective To construct 3D finite element model of the thoracolumbar spinal cord, and study the mechanism of spinal cord injury caused by burst fracture through biomechanical experiments. Methods The compression simulation on burst fracture was performed using finite element technology, and the results were verified by comparing the tested models with the in vivo and in vitro experimental results. Results The strain distribution in white matter of the spinal cord was higher than that in grey matter at the initial stage of burst fracture. As the displacement of bony fragments increased, the strain distribution in grey matter increased subsequently. But when the displacement of bony fragments finally reached the maximum, the strain in white matter was higher than that in grey matter. Conclusions Traumatic severity of the spinal cord during burst fracture is dependent on the posterior encroachment, and the traumatic procedure order for ventral horn (motor function) or dorsal horn (sensory function) of cord tissue also plays an important role in the evaluation. In clinical practice, the patient’s condition can be evaluated more accurately by assessing severity of the spinal motor and sensory functions. Further understanding on strain distribution in the spinal cord during the injury may inspire new strategies for treating or preventing spinal cord injury.
RÉSUMÉ
Objective To optimize the design of ball socket of artificial cervical joint complexity. Method A three dimension model of the artificial cervical joint complexity was constructed by the finite element method. The height range of the ball socket handle in the model was set. A simulation was manipulated to optimize the height under the physical load. The stress and strain of the joint complexity with different sizes was analyzed and the systematic safety factor was also evaluated. Results The simulation showed that the maximum Von mises stress appeared at the joint of handle and bottom in the anteflexion position. As the height of the handle increased, the maximum strain increased, and the graph of minimum safety factor was Parabola curve. Conclusions Considering the systematic stability and mobility, when the height of handle is 6 mm, the design of ball socket is considered to be optimal.
RÉSUMÉ
Objective To study the stress distribution on different length of pedicle screws under the physiological load by using the three dimensional finite element analysis. Method A three dimension model of the pedicle screw and L1 vertebral body were constructed with the model meshed on the basis of the finite element method. The feature dimension of pedicle screw in the model was set in a specified varied range. Under the physiological load, the stress on every model with different diameter sizes of pedicle screw was analyzed. ResultsThe stress on every bone model decreased with the increase of stress on screw under the axially pullout force as the length of screw ranged from 30mm to 50mm. And the maximum Equivalent Stress (EQV Stress) in the pedicle screw appeared in the central area of the pedicle screw, the maximum Equivalent Stress (EQV Stress) in the cortical bone appeared in both sides of contact surface, the maximum Equivalent Stress (EQV Stress) of the cancellous bone appeared in both sides of contact surface of the top of pedicle screw and cancellous bone. In a certain external load, with the 50mm length of screw, the load that transfers to the cortical bone and cancellous bone is reduced by 43.1% and 42.3%, respectively, while the maximum Equivalent Stress (EQV Stress) of screw was increased 38%. When L≥45mm, the variable stress on all models become stable. Conclusions While the length of screw is in range of 4.0 mm to 6.5 mm, 30～50 mm ,the increase of pedicle screw length could improve the distribution of axial pullout stress on the screws, cortical bone and cancellous bone. As long as the bone mass allowed, the length of pedicle screws should be not less than 45mm in clinical choice.