ABSTRACT
Objective To compare the stability effect of the fixation segment using the new test system based robotics to simulate the complex human movement at natural state about the three-level fixa-tion by using four, five or six pedicle screws in treatment of thoracolumbar burst fractures. Methods Six human cadaveric spines were dissected from T_(11)-L_3. The inferior half part of L_1 vertebral bodies and L_1-L_2 dises were resected to mimie an unstable L_1 burst fracture with loss of anterior column support. Specimens were tested in accordance with the following order:intact, 4,5 and 6 pedicle screws fixation at the three-level fixation. The range of motion (ROM) of the fixation segment (T_(11)-L_3) was measured with the six-freedom degree robotics system controlled by mixed force and displacement during flexion, exten-sion, lateral bending and axial torsion, when the stiffness was calculated. One-way statistieal analysis was used for analyzing the collected data. Results With increased number of screws, the ROM of the fixa-tion segment (T_(11)-L_3) was gradually decreased and the stiffness gradually increased. The ROM under ax-ial rotation of six and five screws group became smaller than four screws group (P < 0.05). The stiffness under axial rotation of six screws group was higher than four screws group (P < 0.05). There was no sta-tistical difference between five screws group and four screws group in regard of the stiffness in axial rota-tion (P > 0.05). There were no significant differences in ROM and stiffness under six different loading directions between six screws group and five screws group (P > 0.05). No statistical difference was observed for three fixation modes in aspects of ROMs and stiffness under flexion-extension or lateral ben-ding (P > 0.05). Conclusions Three-level fixation of burst fractures with five or six screws offers im-proved biomechanical stability compared with traditional four screws fixation. But the difference is insig-nificant between six and five screws fixations.
ABSTRACT
Objective To develop self-locking cannulated compression anti-rotation blade and investigate its design characteristic and manipulation techniques. Methods Femoral neck fracture model was made by osteotomy on seven cadaver femurs and then fixed by self-locking cannulated compres-sion anti-rotation blade under fluoroscopic guidance according to designed procedures. After fixation, bio-mechanic test was performed to evaluate fixation stability. Results Cannulated self-locking compres-sion anti-rotation blade was tightly impacted in proximal femur and compression detected during the process of locking, with successful manipulation and stable fixation. Conclusion Because of advanced design characteristic and simple manipulation, self-locking cannulated compression anti-rotation blade can be a substitute for cannulated cancellous lag screw in treatment of femoral neck fractures.
ABSTRACT
Objective To observe the anatomical and biomechanieal properties of the forearm in terosseous membrane (IOM), providing the scientific theoretical basis for the diagnosis and treatment of the IOM injury. Methods Ten radius-IOM-ulna structures (left for 5 and right for 5) were harvested from 5 fresh-frozen adult cadavers to measure the length, width and thickness of the tendinous part. Then the tendi-nous part with its radial and ulnar insertions were isolated, embedding the proximal part of the radius and the distal part of the ttina in commercially available dental base acrylic resin powder. The embedded speci-mens were mounted on MTS 858 testing machine using a 10 000 N load cell for all tensile tests. The speci-mens were tested at a displacement rate of 50 mn/min until failure. The load-displacement curve was de-scribed by the computer while the maximum load and stiffness were recorded. Results The IOM consisted of three components: the tendinous part, the membranous part, and the dorsal oblique accessory cord. The IOM was fiat in the neutral position, while it flexed during the pronation and supination. Six specimens ob-tained the tear of tendinous portion at a maximum load of (1021.50±250.13) N. The stiffness was (138.24±24.29) N/mm with displacement to failure of (9.77±1.77) mm. Other 4 specimens failed by fracture through the ulnar fixed site before there was failure of the IOM at a maximum load of (744.40±109.85) N. The stiff-ness was (151.17±30.68) N/mm with displacement to failure of (6.51±0.51) ram. Conclusion The IOM has stiffness comparable to the ligament between the radius and the ulna and play an important role for the maintenance of longitudinal stability of the forearm. These results can provide objective criteria for the eval-uation of reconstructive methods.
ABSTRACT
Objective To observe the biomechanics of the anterior and posterior interosseous talo-calcaneal ligaments (ITCLs) . Methods Load-displacement characteristics of the subtalar joint were studied in 12 cadaver specimens whose ankle joints were mutilated. The ankle articular surfaces of the talus and the post-calcaneus were exposed. Bone blocks were then embedded in polymethylmethacrylate. The an-terior ITCLs were abscised in 6 of them, and the posterior ITCLs in the other 6. A multi-functional biome-chanical machine was used to perform the biomechanical tests on the specimens. Results When the anterior ITCLs were cut, the tali moved to the anterior-lateral side. When the posterior ITCLs were cut, the tali mostly moved to the anterior-interior side. Conclusions The anterior and posterior ITCLs have dif-ferent roles in maintaining stability of the subtalar joint. Since the posterior ITCLs seem more important than the anterior ones, they should have priority in ITCL reconstruction.