3D finite analysis on injury mechanism of spinal cord compression / 医用生物力学

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.

Application of two different pedicle screw augmentation techniques used for in vitro sheep osteoporotic vertebra model / 医用生物力学

Objective To determine the effects of the two kinds of pedicle screws with cement augmentation used for in vitro sheep osteoporotic vertebra model. Method Forty osteoporosis specimens of lumbar vertebrae demineralized by decalcification solution were complete randomly devided into four groups including Group A (only screw),Group B (whole trajectory filled with PMMA),Group C1(partial trajectory filled with PMMA) and Group C2 (partial trajectory filled with PMMA). Osteoporosis specimens from four groups were tested by bone mineral density (BMD) and observed by spiral CT and MicroCT. The maximum force and energy absorption of pedicle screw were tested. Results BMD in each group were averagely declined about 25%～30% (P>0.05), so osteoporotic vertebrae model was successfully established.Spiral CT and MicroCT showed that screw of Group B was fully surrounded by PMMA, which constituted screw PMMA-bone interface,while screw of Group C2 was partially surrounded by PMMA, which constituted partial screw-bone and partial screw PMMA-bone interface. The axial pull-out test showed that the maximum force (Fmax) and its energy absorption in Group B, C1,2 were significantly higher than those in Group A（P0.05). Conclusions Both the whole and partial pedicle screw augmentation can significantly improve the strength of pedicle screw in the context of osteoporosis. The latter not only formed a special whole interface consisting of partial “screw-bone” and partial screw-CSC-bone interface,but produced the strengthening effect equivalent to the former by increasing injection doses of PMMA.

Optimal design of ball socket on artificial cervical joint complexity by finite element analysis / 医用生物力学

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.

Micro-CT evaluation and histological analysis of screw-bone interface of expansive pedicle screw in osteoporotic sheep / 中华创伤杂志(英文版)

<p><b>OBJECTIVE</b>To investigate the properties of screw-bone interface of expansive pedicle screw (EPS) in osteoporotic sheep by micro-CT and histological observation.</p><p><b>METHODS</b>Six female sheep with bilateral ovariectomy-induced osteoporosis were employed in this experiment. After EPS insertion in each femoral condyle, the sheep were randomly divided into two groups: 3 sheep were bred for 3 months (Group A), while the other 3 were bred for 6 months (Group B). After the animals being killed, the femoral condyles with EPS were obtained, which were three-dimensionally-imaged and reconstructed by micro-CT. Histological evaluation was made thereafter.</p><p><b>RESULTS</b>The trabecular microstructure was denser at the screw-bone interface than in the distant parts in expansive section, especially within the spiral marking. In the non-expansive section, however, there was no significant difference between the interface and the distant parts. The regions of interest (ROI) adjacent to EPS were reconstructed and analyzed by micro-CT with the same thresholds. The three-dimensional (3-D) parameters, including tissue mineral density (TMD), bone volume fraction (BVF, BV/TV), bone surface/bone volume (BS/BV) ratio, trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp), were significantly better in expansive sections than non-expansive sections (P less than 0.05). Histologically, newly-formed bony trabeculae crawled along the expansive fissures and into the center of EPS. The newly-formed bones, as well as the bones at the bone-screw interface, closely contacted with the EPS and constructed four compartments.</p><p><b>CONCLUSIONS</b>The findings of the current study, based on micro-CT and histological evaluation, suggest that EPS can significantly provide stabilization in osteoporotic cancellous bones.</p>

Treatment of ipsilateral femoral neck and shaft fractures / 中华创伤杂志(英文版)

<p><b>OBJECTIVE</b>To investigate the clinical characteristics, treatment options and causes of misdiagnosis of ipsilateral femoral neck and shaft fractures.</p><p><b>METHODS</b>Among 20 patients with ipsilateral femoral neck and shaft fractures, 19 were treated operatively and 1 was treated conservatively. Sixteen cases of femoral shaft fractures were treated by open reduction and internal fixation with compressive plate, and 2 cases were treated with interlocking intramedullary nailing. Eighteen femoral neck fractures were treated with cannulated screws. Another patient was treated with proximal femoral nail to fix both the neck and shaft. Delayed diagnosis for femoral neck fractures occurred in 2 cases preoperatively.</p><p><b>RESULTS</b>A total of 19 patients were followed up. The follow up period ranged from 5 to 48 months with an average of 15 months. All the fractures were healed.</p><p><b>CONCLUSION</b>For case of femoral shaft fracture caused by high energy injury, an AP pelvic film should be routinely taken. Once the femoral neck fracture is recognized, operative reduction and fixation should be performed in time. Femoral neck and shaft fractures should be fixed separately.</p>

Treatment of nonunions of humeral fractures with interlocking intramedullary nailing / 中华创伤杂志(英文版)

<p><b>OBJECTIVE</b>To introduce the experience of treating nonunions of humeral fractures with interlocking intramedullary nailing.</p><p><b>METHODS</b>Twelve patients with humeral nonunions were treated with interlocking intramedullary nailing. The time interval between trauma and surgery was 10.5 months on average. Open reduction with anterograde approach was performed. Axial compression was specially applied to the fracture site with humeral nail holder after insertion of distal locked screws. Iliac bone grafting was added.</p><p><b>RESULTS</b>The average follow-up period was 21 months (ranging 9-51 months). All patients achieved osseous union 5.8 months after treatment on average. Eleven patients had good functions of the shoulder joints and the upper extremities. No patient experienced any permanent neurological deficit. Refracture of the original ununited region occurred in one patient after removal of the internal fixator one year later, but union was achieved after closed re-intramedullary nailing fixation.</p><p><b>CONCLUSION</b>Humeral interlocking intramedullary nailing is an effective alternative treatment for humeral nonunion.</p>

Micro-CT evaluation and histological analysis of screw-bone interface of expansile pedicle screw in osteoporotic sheep / 中华外科杂志

<p><b>OBJECTIVE</b>To investigate the properties of screw-bone interface of expansive pedicle screw (EPS) in osteoporotic sheep using micro-CT and histology.</p><p><b>METHODS</b>Six female sheep with bilateral ovariectomy-induced osteoporosis were employed in this experiment and were randomly assigned into 2 groups: A and B. After EPS insertion in each femoral condyles, sheep in group A were bred for 3 months, while those in group B 6 months. Femoral condyles with EPS were 3D-imaged and reconstructed by micro-CT. Histology was evaluated thereafter.</p><p><b>RESULTS</b>The trabecular microstructure was denser at the screw-bone interface than in the distant parts in expansive section, especially within spiral marking. In the non-expansive section, however, there was no significant difference between the interface and the distant parts. The regions of interest (ROI) adjacent to EPS were reconstructed and analyzed by micro-CT using the same thresholds. The 3D-parameters generated, including tissue mineral density (TMD), bone volume fraction (BVF, BV/TV), bone surface/bone volume (BS/BV) ratio, trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp), were significantly better in expansive than in non-expansive sections (P < 0.05). Histologically, newly formed bone trabeculae crawled along the expansive fissures and into the center of EPS. The newly formed bones, as well as the bone at the bone-screw interface, closely contacted the EPS and constructed four compartments.</p><p><b>CONCLUSIONS</b>Based on micro-CT and histological evaluation, the study suggest that EPS can significantly provide stabilization in osteoporotic cancellous bone.</p>

Biomechanical evaluation of an expansive pedicle screw in calf vertebrae / 中华创伤杂志(英文版)

<p><b>OBJECTIVE</b>To obtain a comprehensive understanding of the effect of the improvement of fixation strength of a newly designed expansive pedicle screw through biomechanical analyses.</p><p><b>METHODS</b>100 (200 pedicles) fresh calf lumber vertebrae were used. A total of four instrumentation systems were tested including CDH (CD Horizon), USS (Universal Spine System pedicle screw), Tenor (Sofamor Denek) and expansive pedicle screw (EPS). Pullout and turning-back tests were performed to compare the holding strength of the expansive pedicle screw with conventional screws, i.e. USS, CDH and Tenor. Revision tests were performed to evaluate the mechanical properties of the expansive pedicle screw as a "rescue" revision screw. A fatigue simulation using perpendicular load up to 1,500,000 cycles was carried out.</p><p><b>RESULTS</b>The turning back torque (Tmax) and pull-out force (Fmax) of EPS were significantly greater than those of USS, Tenor and CDH screws (6.5 mm x 40 mm). In revision tests, the Fmax of both kinds of EPS (6.5 mm x 40 mm; 7.0 mm x 40 mm) were greater than that of CDH, USS and Tenor screws significantly (P<0.05). No screws were broken or bent at the end of fatigue tests.</p><p><b>CONCLUSIONS</b>EPS can significantly improve the bone purchase and the pull-out strength compared to USS, Tenor and CDH screws with similar dimensions before and after failure simulation. The fatigue characteristic of EPS is similar to that of CDH, USS and Tenor screws.</p>