Isao Ohnishi

Nonlinear finite element model predicts vertebral bone strength and fracture site.

Study Design. A study on computed tomography (CT)-based finite element (FE) method that predicts vertebral strength and fracture site using human cadaveric specimens. Objective. To evaluate the accuracy of the nonlinear FE method by comparing the predicted data with those of mechanical testing. Summary of Background Data. FE methods may predict vertebral strength and fracture site but the prediction has been difficult because of a complex geometry, elastoplasticity, and thin cortical shell of the vertebra. Methods. FE models of the 12 thoracolumbar vertebral specimens were constructed. Nonlinear FE analyses were performed, and the yield load, the fracture load, the sites where elements failed, and the distribution of minimum principal strain were evaluated. A quasi-static uniaxial compression test for the same specimens was conducted to verify these analyses. Results. The yield loads, fracture loads, minimum principal strains, and fracture sites of the FE prediction significantly correlated with those measured. Conclusions. Nonlinear FE model predicted vertebral strength and fracture site accurately.

Prediction of proximal femur strength using a CT-based nonlinear finite element method: differences in predicted fracture load and site with changing load and boundary conditions.

The annual occurrence of hip fracture due to osteoporosis as of 2002 had reached 120,000 in Japan. The increase has been very rapid. From a biomechanical perspective, hip fractures are thought to be caused in real settings by different directions of loading. Thus, clarification of the loading directions under which the proximal femur is most vulnerable to fracture would be helpful for elucidating fracture mechanics and establishing preventive interventions. The purpose of the current study was to clarify the influence of loading direction on strength and fracture site of the proximal femur using the CT-based nonlinear FE method to determine loading directions under which the proximal femur is most vulnerable to fracture. Contralateral femora were analyzed in 42 women with hip fracture (mean age, 82.4 years), comprising 20 neck fractures and 22 trochanteric fractures. Within 1 week after fracture, quantitative CT of the contralateral femur was performed in each patient and 3-dimensional FE models were created. One stance loading configuration (SC) and four different fall loading configurations (FC) were assigned. Nonlinear FE analysis was performed. Differences in fracture loads depending on differences in loading direction were analyzed and correlations among fracture loads in different loading directions were assessed. Next, fracture sites were also analyzed. Mean predicted fracture load in the SC was 3150 N. Mean fracture loads were 2270 N in FC1, 1060 N in FC2, 980 N in FC3, and 710 N in FC4. The correlation between predicted fracture loads in SC and those in each FC was significant with a correlation coefficient of 0.467-0.631. Predicted fracture sites in the SC appeared at the subcapital region in all patients and were categorized as neck fracture. However, trochanteric fractures occurred in all fall configurations except FC1. In FC1, a significant correlation was seen between real fracture type and predicted type. The current investigation could contribute to the acquisition of useful knowledge allowing the establishment of more efficacious means of preventing hip fractures.

Effect of pulsed electromagnetic fields (PEMF) on late-phase osteotomy gap healing in a canine tibial model

The effects of a pulsed electromagnetic field (PEMF) on late bone healing phases using an osteotomy gap model in the canine mid‐tibia were investigated. A transverse mid‐diaphyseal tibial osteotomy with a 2‐mm gap was performed unilaterally in 12 adult mixed‐breed dogs and stabilized with external fixation. Animals in the variable group (n = 6) were treated with PEMF for 1 h daily starting 4 weeks after surgery for a total of 8 weeks, whereas no stimulation signal was generated in the control group (n = 6). Functional load‐bearing and radiographic assessments were conducted time‐sequentially until euthanasia 12 weeks after surgery. Torsional tests and an analysis of undecalcified histology were performed on the retrieved mid‐tibial diaphysis containing the osteotomy site. In the PEMF group, load‐bearing of the operated limb recovered earlier when compared to the control group (p < 0.05). Load‐bearing in the PEMF group at 8 weeks was greater than in the control group (p < 0.02). The periosteal callus area increased following surgery at 6 weeks (p < 0.05) and thereafter (p < 0.01) in the PEMF group, while a significant increase was observed at 8 and 10 weeks after surgery (p < 0.05) in the control group. Both the normalized maximum torque and torsional stiffness of the PEMF group were significantly greater than those of the control group (p < 0.04 and p < 0.007, respectively). Histomorphometric analyses revealed greater new‐bone formation (p < 0.05) in the osteotomy gap tissue and increased mineral apposition rate (p < 0.04) and decreased porosity in the cortex adjacent to the osteotomy line (p < 0.02) in the PEMF group. PEMF stimulation of 1 h per day for 8 weeks provided faster recovery of load‐bearing, a significant increase in new bone formation, and a higher mechanical strength of the healing mid‐tibial osteotomy. This study revealed enhancing effects of PEMF on callus formation and maturation in the late‐phase of bone healing.

Treatment of congenital pseudarthrosis of the tibia: a multicenter study in Japan.

Treatment of congenital pseudarthrosis of the tibia (CPT) remains a challenge. To clarify the current situation in treatment, a multicenter study was carried out to obtain information on the results of CPT treatment. The objective of this study was to propose appropriate treatment guidelines for CPT. Records of 73 patients with CPT who underwent surgical treatment were collected from 32 hospitals. The modality of the treatment was 26 with Ilizarov technique, 25 with free vascularized fibular graft, 7 with a combination of the two techniques, 6 with intramedullary nailing with free bone grafting, 5 plating with free bone grafting, and 4 with other treatments. Fifty-four procedures resulted in union, 7 resulted in delayed union, 7 were left un-united, 1 underwent amputation, and the results were unknown in 4. According to the results of this study, the most acceptable methods of treatment of CPT are the Ilizarov method and the vascularized fibular graft.

Insulin Secretory Response Is Positively Associated with the Extent of Ossification of the Posterior Longitudinal Ligament of the Spine

Background: Glucose intolerance is frequently found in patients with ossification of the posterior longitudinal ligament of the spine. This study was undertaken to examine the relationship between glucose intolerance and the extent of ossification in patients with ossification of the posterior longitudinal ligament. Methods: A total of 100 patients with ossification of the posterior longitudinal ligament (the overall study group), including fifty-two inpatients who were scheduled to have an operation (the inpatient group) and forty-eight outpatients who had undergone an operation, were analyzed. Indices of glucose metabolism—fasting plasma glucose and serum insulin levels, hemoglobin A1c level, and insulinogenic index (a ratio of the increment of the serum level of insulin to that of glucose)—as well as age and body-mass index were correlated with the extent of ossification, as determined by the number of vertebral levels affected with ossification of the posterior longitudinal ligament (extent of ossification), in the inpatient group. In addition, a similar analysis was performed in twenty-eight inpatients (the selected inpatient group) whose ages and body-mass indices were within one standard deviation of the mean values of those of the inpatient group. Association of a polymorphism in the gene of insulin receptor substrate-1, an essential substrate in insulin signaling, with the extent of ossification was evaluated with genomic DNA extracted from the overall study group. Results: Multiple-regression analysis revealed direct correlations of age (p = 0.038), body-mass index (p = 0.006), and insulinogenic index (p = 0.0003) with the extent of ossification of the posterior longitudinal ligament in the inpatient group. The fasting plasma glucose level, the hemoglobin A1c level, and the stage of glucose tolerance were not associated with the extent of ossification. In the analysis of the selected inpatient group, only the insulinogenic index was correlated with the extent of ossification (p = 0.002). However, no significant association was seen between the insulin receptor substrate-1 polymorphism and the extent of ossification. Conclusions: The insulin secretory response was associated with the extent of ossification of the posterior longitudinal ligament. Since insulin receptor substrate-1 is expressed both in the spinal ligament and in the tissues regulating glucose metabolism, we speculate that some other molecules related to insulin signaling that are impaired only in the tissues regulating glucose metabolism may be responsible for the progression of ossification. We also speculate that the upregulation of insulin production due to the impairment of insulin action may stimulate osteoprogenitor cells in the ligament to induce ossification. Clinical Relevance: The insulinogenic index may be useful as a serum marker for the prediction of progression of ossification of the posterior longitudinal ligament. This study may serve as a stimulus for evaluation of the use of various drugs that may improve the response to insulin in the tissues regulating glucose metabolism to prevent the progression of ossification.

In vivo assessment of lumbar vertebral strength in elderly women using computed tomography-based nonlinear finite element model.

Study Design. In vivo study of a computed tomography (CT)-based nonlinear finite element model (FEM). Objective. To establish an FEM with the optimum element size to assess the vertebral strength by comparing analyzed data with those obtained from mechanical testing in vitro, and then to assess the second lumbar (L2) vertebral strength in vivo. Summary of Background Data. FEM has been reported to predict vertebral strength in vitro, but has not been used clinically. Methods. Comparison among the 3 models with a different element size of 1 mm, 2 mm, and 3 mm was performed to determine which model achieved the most accurate prediction. Vertebral strength was assessed in 78 elderly Japanese women using an FEM with the optimum element size. Results. The optimum element size was 2 mm. The L2 vertebral strength obtained with the FEM was 2154 ± 685 N, and the model could detect preexisting vertebral fracture better than measurement of bone mineral density. Conclusion. The FEM could assess vertebral strength in vivo.

Long-Term Results of Operative Treatment for Cervical Spondylotic Myelopathy in Patients With Athetoid Cerebral Palsy : An Over 10-Year Follow-Up Study

Study Design. A retrospective radiographic and medical record analysis of patients followed for more than 10 years after operative treatment for cervical spondylotic myelopathy complicating athetoid cerebral palsy. Objective. To describe the incidence of late neurologic deterioration and spinal deformity after operative treatment for cervical spondylotic myelopathy in athetoid cerebral palsy. Summary of Background Data. The possibility of recurrence of symptoms after operative treatment for cervical spondylotic myelopathy seems greater in patients with athetoid cerebral palsy because of their involuntary neck movements. Although there are several reports of surgical results, long-term follow-up studies are very rare. Methods. Ten patients with athetoid cerebral palsy were evaluated over an average of 15 years after anterior decompression (corpectomy) and fusion (three patients), laminectomy (one patient), and laminoplasty (six patients, four with accompanying posterior fusion). They averaged 45 years of age at surgery. Surgical results were assessed using Kurokawa’s method. Late neurologic deterioration was based on decrement in the JOA score, and the evolution of kyphosis or instability of the cervical spine was observed radiographically. Results. Surgical results at the most improved period were good or excellent in all 10 patients. Eight showed late neurologic deterioration, however, and six of them deteriorated from 8 to 13 years after surgery, largely because of progressive deformity. Conclusions. Long-term follow-up evaluation is essential in any type of operation, particularly with patients with athetoid cerebral palsy who often undergo this operation in their 30s or 40s.

Prediction of Vertebral Strength Under Loading Conditions Occurring in Activities of Daily Living Using a Computed Tomography-Based Nonlinear Finite Element Method

Study Design. A clinical study on osteoporotic vertebral strength in daily living using a computed tomography (CT)-based nonlinear finite element (FE) model. Objective. To evaluate the differences in predicted fracture strength of osteoporotic vertebral bodies among the different loading conditions that are occurring in the activities of daily living. Summary of Background Data. FE model has been reported to predict vertebral strength in uniaxial loading, but forward bending load plays an important role in osteoporotic vertebral fractures. Methods. Strengths of the second lumbar vertebra in 41 female patients with postmenopausal osteoporosis were analyzed using a nonlinear CT-based FE method. Three different loading conditions were adopted uniaxial compression, forward bending, and erect standing. The same boundary condition was used for all loading conditions. Predicted strengths under forward bending and erect standing were compared with that under uniaxial compression and differences in strength were statistically analyzed. Results. The regression equation relating strength under uniaxial compression to that under erect standing was expressed as y = 0.8912x + 19.332 (R = 0.9522), whereas the equation relating uniaxial compression to forward bending was y = 0.7033x + 55.071 (R = 0.8342). Both relationships were significant, but the correlation between forward bending and uniaxial compression was not strong, while strength was lower under forward bending than under uniaxial compression according to the Friedman multiple comparison test (P = 0.00017). Conclusion. Strength under forward bending correlated significantly to that under uniaxial compression, but the correlation was not strong. Therefore, in osteoporotic patients, both uniaxial compression and forward bending should be assessed to evaluate fracture risk in daily living using a CT-based FE method.

The role of calcium metabolism abnormalities in the development of ossification of the posterior longitudinal ligament of the cervical spine

To study the role of calcium metabolism in the development of ossification of the posterior longitudinal ligament of the cervical spine, 39 patients with affected cervical spines were investigated using an oral calcium tolerance test and followed by cervical spinal radiography to evaluate disease progression. The average follow-up was 6 years. The patients were divided into two groups according to their responsiveness to an oral calcium load: a group of 14 patients with decreased calciuric responses and another group of 25 with normal responses. The incidence of the development of cervical ossification of the posterior longitudinal ligament in the decreased-response group was significantly higher than that in the normal group. Because these patients were managed operatively by laminoplasty, however, the incidence was low irrespective of their calciuric responses. These results suggest that the development of cervical ossification of the posterior longitudinal ligament is associated with decreased intestinal caicium absorption but that treatment with laminoplasty alters the mechanical environment of the cervical spine (eg, range of motion of the cervical spine is limited). The development of cervical ossification of the posterior longitudinal ligament may be controlled by this procedure.

Autogenous Onlay Grafting for Enhancement of Extracortical Tissue Formation Over Porous-Coated Segmental Replacement Prostheses*

BACKGROUND Prosthetic reconstruction with extracortical bone-bridging is an effective method of limb salvage after resection of a malignant or locally invasive benign bone tumor. Use of cancellous bone graft alone is less effective in achieving extracortical bone-bridging. The present study was performed to investigate the effects of a corticocancellous onlay graft on bone and soft-tissue formation over a porous-coated replacement prosthesis in the mid-diaphyseal region of canine femora. METHODS Bilateral resection of a six-centimeter segment of the femoral diaphysis and reconstruction with a porous-coated segmental prosthesis was performed in six mongrel dogs. In one limb (the experimental side), eight strips of corticocancellous bone were evenly placed around the junctions between the femur and the prosthetic surface. Cancellous bone was placed under and between the strips of cortical bone. No graft was used in the other limb (the control side). The animals were followed for twelve weeks, with sequential assessments of load-bearing and radiographic evaluation. Biomechanical, histological, and microradiographic analyses of the specimens were performed after death. RESULTS On the control side, load-bearing at four weeks postoperatively was significantly decreased compared with the preoperative value (p<0.05); no difference in these values could be detected on the experimental side. Both the area of the callus and the contact area between the bone and the prosthetic shoulder were greater on the experimental side (p<0.05). The mechanical stiffness and the maximum torque at failure of the extracortical bridging tissue across the junction between the bone and the prosthetic shoulder were eighteen (p<0.007) and five times greater (p<0.05), respectively, on the experimental side. CONCLUSIONS Extracortical bone-bridging was accomplished with corticocancellous onlay bone-grafting. Without bone-grafting, bone formed only occasionally. Bone-grafting also enhanced the formation of a soft-tissue capsule around the prosthesis.