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Objective: The objective of this study was to investigate the factors that affect the predicted bone strength of proximal femur in Japanese population., Methods: Participants (552 men and 273 women) in a health checkup program with computed tomography (CT) at the University of Tokyo Hospital were enrolled in this study. Three-dimensional finite element models of the proximal femur were constructed from CT data of the participants with simultaneous scans of a calibration phantom containing hydroxyapatite rods. Multiple regression analysis was performed to analyze the relationship between the predicted bone strength and clinical factors., Results: Average predicted strength of proximal femur was lower in women than in men in all age ranges. Predicted bone strength in women under both stance and fall configurations significantly decreased with age, and that in men had the tendency to decrease with age. Body weight positively affected the predicted bone strength in both men and women., Conclusions: This is the first cross-sectional analysis of the predicted bone strength of the proximal femur in Japanese population of wide age range. Age and body weight critically affected bone strength of proximal femur determined by quantitative CT-based finite element method, in particular in women, under both stance and fall configurations.

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.

We have developed a surgical robotic system for femoral fracture reduction employing indirect traction. Indirect traction in fracture reduction is a generally used surgical method for preventing complications such as bone splits caused by high stress on bones. For traction, a patient's foot is gripped by a jig and pulled to the distal side. Indirect traction has the advantage of distributing bone stress by utilizing a strong traction force; however, this procedure does not accurately control the proper positioning of fractured fragments when a surgical robot is used. The human leg has knee and an ankle joints, and thus robotic motion presents problems in not being able to directly propagate reduction motion to a fractured femoral fragment, rendering control of bone position difficult. We propose a control method for fracture reduction robots using external force/torque measurements of the human leg to achieve precise fracture reduction. Results showed that the proposed method reduced repositioning error from 6.8 mm and 15.9 degrees to 0.7 mm and 5.3 degrees, respectively.

Hip fractures are the most serious complication of osteoporosis and have been recognized as a major public health problem. In elderly persons, hip fractures occur as a result of increased fragility of the proximal femur due to osteoporosis. It is essential to precisely quantify the strength of the proximal femur in order to estimate the fracture risk and plan preventive interventions. CT-based finite element analysis could possibly achieve precise assessment of the strength of the proximal femur. The purpose of this study was to create a simulation model that could accurately predict the strength and surface strains of the proximal femur using a CT-based finite element method and to verify the accuracy of our model by load testing using fresh frozen cadaver specimens. Eleven right femora were collected. The axial CT scans of the proximal femora were obtained with a calibration phantom, from which the 3D finite element models were constructed. Materially nonlinear finite element analyses were performed. The yield and fracture loads were calculated, while the sites where elements failed and the distributions of the principal strains were determined. The strain gauges were attached to the proximal femoral surfaces. A quasi-static compression test of each femur was conducted. The yield loads, fracture loads and principal strains of the prediction significantly correlated with those measured (r=0.941, 0.979, 0.963). Finite element analysis showed that the solid elements and shell elements in undergoing compressive failure were at the same subcapital region as the experimental fracture site.

Background: The purpose of this study was to investigate the effects of lengthening frequency on mechanical environment in limb lengthening., Methods: Tensile forces were continuously monitored using a load sensor attached to a unilateral external fixator. Twenty patients were monitored. Ten patients were with acquired femoral shortening, and five of them underwent quasi-continuous lengthening of 1440 steps per day, and the other five received step lengthening twice a day. The other 10 patients were with achondropalsia. Five of them underwent the same quasi-continuous lengthening, and the other five received the same step lengthening. The circadian change and the daily course of the tensile forces were assessed and compared between quasi-continuous lengthening and step lengthening., Findings: As for circadian change, an acute increase in the force took place simultaneously with each step of lengthening in the step-lengthening group, but very little change of the baseline force level was seen during quasi-continuous lengthening. As for daily course of the tensile force, it increased almost linearly in both lengthening frequency groups in the initial stage of lengthening. No significant difference of the average force increment rate in this phase was recognized between the quasi-continuous and step lengthening groups irrespective of the etiologies., Interpretation: The lengthening frequency greatly affected the circadian change of the tensile force, but did not affect the increment rate of the force in the linear phase.