Satoru Ohashi

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.

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.

Effect of low-intensity pulsed ultrasound stimulation on callus remodelling in a gap-healing model: EVALUATION BY BONE MORPHOMETRY USING THREE-DIMENSIONAL QUANTITATIVE MICRO-CT

We evaluated the effect of low-intensity pulsed ultrasound stimulation (LIPUS) on the remodelling of callus in a rabbit gap-healing model by bone morphometric analyses using three-dimensional quantitative micro-CT. A tibial osteotomy with a 2 mm gap was immobilised by rigid external fixation and LIPUS was applied using active translucent devices. A control group had sham inactive transducers applied. A region of interest of micro-CT was set at the centre of the osteotomy gap with a width of 1 mm. The morphometric parameters used for evaluation were the volume of mineralised callus (BV) and the volumetric bone mineral density of mineralised tissue (mBMD). The whole region of interest was measured and subdivided into three zones as follows: the periosteal callus zone (external), the medullary callus zone (endosteal) and the cortical gap zone (intercortical). The BV and mBMD were measured for each zone. In the endosteal area, there was a significant increase in the density of newly formed callus which was subsequently diminished by bone resorption that overwhelmed bone formation in this area as the intramedullary canal was restored. In the intercortical area, LIPUS was considered to enhance bone formation throughout the period of observation. These findings indicate that LIPUS could shorten the time required for remodelling and enhance the mineralisation of callus.

A New Method for Evaluation of Fracture Healing by Echo Tracking

Assessment of bone healing on radiographs depends on the volume and radio-opacity of callus at the healing site, but is not necessarily objective, and there are differences of judgment among observers. To overcome this disadvantage, a clinical system was developed to quantify the stiffness of healing fractures of the tibia in patients by the echo tracking (ET) method in a manner similar to a three-point bending test. The purpose of this study was to ensure that the ET system could clinically assess the progress, delay or arrest of healing. The fibular head and the lateral malleolus were supported. A 7.5-MHz ultrasound probe was placed on the proximal and distal fragments and a load of 25 N was applied. Five tracking points were set along the long axis of the ultrasound probe at intervals of 10 mm. With a multiple ET system, two probes measured the displacement of five tracking points on each of the proximal and distal fragments of the tibia, thereby detecting the bending of the two fragments generated by the load. ET angle was defined as the sum of the inclinations of the proximal and distal fragments. Eight tibial fractures in seven patients treated by a cast or internal fixation were measured over time. In patients with radiographically normal healing, the bending angle decreased exponentially over time. However, in patients with nonunion, the angle remained the same over time. It was demonstrated that the ET method could be clinically applicable to evaluate fracture healing as a versatile, quantitative and noninvasive technique.

Distraction osteogenesis promotes angiogenesis in the surrounding muscles.

Distraction osteogenesis is used to treat atrophic nonunion and focal osteomyelitis. It enhances blood vessel formation in the distracted callus and in the surrounding soft tissues. Long-term angiogenesis, however, is not well described. We hypothesized newly formed blood vessels persist in the surrounding muscles until the late consolidation period. We performed unilateral tibial lengthening in eight adult Beagles. Seven days after tibial osteotomy, we began lengthening for 30 days, following which consolidation was allowed to proceed for another 60 days. We took bilateral microangiograms of the bilateral tibialis anterior, extensor digitorum longus, and gastrocnemius muscles. We determined the blood vessel volume density and the longitudinal and transverse microangiographic scores. The number of blood vessels in specified diameter ranges was determined histologically. The blood vessel volume density of the distracted limb was higher in all three muscles. The longitudinal microangiographic score was higher for the tibialis anterior and extensor digitorum longus muscles on the distracted side, whereas the transverse microangiographic score was not higher. Histologically, the number of blood vessels less than 100 μm in diameter on the distracted side was higher in the tibialis anterior and extensor digitorum longus muscles. Our data suggest distraction osteogenesis activates angiogenesis and maintains increased vascularity until the late consolidation period.

Effect of vascularity on canine distracted tibial callus consolidation.

In the consolidation period of distraction osteogenesis, mineralization occurs before corticalization. We hypothesized that the increased rate of bone mineral density correlates to the density of vascularity in the callus. We unilaterally lengthened the tibia in eight adult beagles. After a waiting period of 7 days, tibiae were lengthened for 30 days. After a consolidation period of an additional 60 days, all animals were euthanized. Just before euthanasia, blood vessels were perfused with 50% w/v barium sulfate solution, and soft radiographs of the distracted callus and the control tibiae were taken. Bone mineral density of the regenerated bones was measured preoperatively by quantitative computed tomography on Days 37, 68, and 98. Increases of the percent bone mineral density (from Day 37 to Day 98 and from Day 68 to Day 98) correlated with the blood vessel volume density ratios on Day 98. Our results suggest that preservation of the higher density of blood vessels in the consolidation period could lead to the better mineralization of the distracted callus.

Surgical Tool Alignment Guidance by Drawing Two Cross-Sectional Laser-Beam Planes

Conventional surgical navigation requires for surgeons to move their sight and conscious off the surgical field when checking surgical tools positions shown on the display panel. Since that takes high risks of surgical exposure possibilities to the patients body, we propose a novel method for guiding surgical tool position and orientation directly in the surgical field by a laser beam. In our navigation procedure, two cross-sectional planar laser beams are emitted from the two laser devices attached onto both sides of an optical localizer, and show surgical tools entry position on the patients body surface and its orientation on the side face of the surgical tool. In the experiments, our method gave the surgeons precise and accurate surgical tool adjusting and showed the feasibility to apply to both of open and percutaneous surgeries.

A Robot Assisted Hip Fracture Reduction with a Navigation System

A fracture reduction robot is described as assisting in safe and precise fracture reduction. The robot is connected with pins that are inserted into the patients bone fragments, together with a customized jig. The robot has six degrees of freedom with high precision, so that precise fracture reduction can be conducted. The failsafe unit of the fracture reduction robot can mitigate excessive reduction force that may cause complications such as avascular necrosis. We have integrated the fracture reduction robot with a navigation system that tracks the relative position of the bone fragments and generates the reduction path. The integrated system is evaluated with the simulated fracture reduction of a hip fracture model (n = 8). Three-dimensional parameters related to the mechanical axis--the proximal femur angle, the distal femur angle, and the length of the mechanical axis--were evaluated by comparing the normal values with those after reduction; these average differences are 1.76 degrees , 0.28 degrees and 0.76mm, respectively. The automated fracture reduction feature makes it possible for medical staff to work at a distance from radiation sources; for patients, the integrated fracture reduction system has the potential to reduce fractures with high precision.

The impact of joint disease on the Modified Health Assessment Questionnaire scores in rheumatoid arthritis patients: A cross-sectional study using the National Database of Rheumatic Diseases by iR-net in Japan

Abstract Objectives: To investigate the effect of bilateral and unilateral joint disease on the Modified Health Assessment Questionnaire (MHAQ) scores and the differences in joint weighting in rheumatoid arthritis patients. Methods: A total of 9212 subjects from the Japanese nationwide cohort database NinJa, 2011, were analyzed. The presence or absence of disease in each joint, including swelling and/or tenderness, was investigated. The correlations between bilateral and unilateral disease in each joint and MHAQ scores were investigated using multivariable logistic regression analysis. Results: The patients’ mean age and disease duration was 63.2 and 12.2 years, respectively. The Disease Activity Score-28 was 3.3. The odds ratios of physical impairment according to the MHAQ using multivariable logistic regression models for bilateral and unilateral joints, respectively, were: shoulder, 4.0 and 1.8; elbow, 2.6 and 1.8; wrist, 1.9 and 1.5; hip, 1.7 and 3.0; knee, 2.6 and 1.9; ankle, 2.3 and 2.0, finger, 1.4 and 1.2; and toe, 1.0 and 1.1. The shoulder, elbow, wrist, knee, and ankle had a significant effect on physical impairment. Conclusions: The MHAQ score was significantly affected by shoulder, elbow, wrist, knee, and ankle joint disease. Furthermore, bilateral disease tended to have a greater effect on physical impairment than unilateral disease.

Measurement of mechanical properties on gap healing in a rabbit osteotomy model until the remodeling stage

BACKGROUND The most important issue in the assessment of fracture healing is to acquire information about the restoration of the mechanical integrity of bone. Many researchers have attempted to monitor stiffness either directly or indirectly for the purpose of assessing strength, as strength has been impossible to assess directly in clinical practice. The purpose of this study was thus to determine the relationship between bending stiffness and strength using mechanical testing at different times during the healing process. METHODS Unilateral, transverse, mid-tibial osteotomies with a 2-mm gap were performed in 28 rabbits. The osteotomy site was stabilized using a double-bar external fixator. The animals were divided into four groups (n=7/group/time point; 4, 6, 8 and 12 weeks). A series of images from micro-computed tomography of the gap was evaluated to detect the stage of fracture healing and a 4-point bending test was performed to measure stiffness and strength. Relative stiffness and strength values were also acquired from calculation of ratios relative to those of the non-osteotomized contralateral bones. FINDINGS Formation of cortex and medullary canal at the gap was seen in the 12-week group and would represent the remodeling stage. In addition, the relationship between stiffness and strength remained almost linear until at least 12 weeks. However, stiffness recovered much more rapidly than strength. INTERPRETATION Strength was not fully restored until the later stages of fracture healing. However, the current study demonstrated that stiffness could be monitored as a surrogate marker of strength until at least the remodeling stage.