Kenji Tobita

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 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.

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.

Evaluation of the accuracy of articular cartilage thickness measurement by B-mode ultrasonography with conventional imaging and real-time spatial compound ultrasonography imaging.

The present study aimed to quantify the thickness of articular cartilage (Tc) in vitro using both conventional and real-time spatial compound B-mode ultrasonography (US) with a clinically used transducer and to evaluate the accuracy of measurement by comparing the results with values obtained microscopically. Femoral condyle samples were obtained from a 6-month-old pig and a 3-year-old pig. B-mode US images with conventional imaging and real-time spatial compound imaging (RTSCI) of osteochondral blocks were acquired. Tc determined using US (Tc-US) was measured from line data parallel to US beam direction acquired from B-mode images with an objective method for determining cartilage surface and bone-cartilage interfaces at the peak brightness values. Tc was also determined under microscopy (Tc-optical) using the corresponding points from US measurement. Tc-US was compared with Tc-optical to assess accuracy. Tc-US correlated significantly with Tc in both conventional imaging and RTSCI (r = 0.961, 0.976, respectively). Bland-Altman plots showed mean differences between Tc-optical and Tc-US were -0.0073 mm and 0.0139 mm with standard deviations of 0.171 mm and 0.131 mm for conventional imaging and RTSCI, respectively. Our results show that Tc-US measurement using B-mode US allows accurate measurement of Tc. Considering correlation coefficients between Tc-US and Tc-optical, RTSCI US may offer higher accuracy for measuring Tc than conventional methods when an objective tissue border determination algorithm is used, even though both showed good accuracy in our study.

Measurement of Articular Cartilage Thickness Using a Three-Dimensional Image Reconstructed from B-Mode Ultrasonography Mechanical Scans Feasibility Study by Comparison with MRI-Derived Data

The present study aimed to develop a method to measure three-dimensional (3-D) thickness of cartilage (Tc) at the femoral condyle using B-mode ultrasonography (US) and to clarify the feasibility of US in clinical evaluations of articular cartilage by comparing the results with 3-D measurement values using magnetic resonance imaging (MRI) and assessing repeatability. The medial surface of the right knees of two healthy male volunteers (age, 37 and 59 years) and the knees on affected side of three male patients with osteoarthritis (OA) (age, 73, 81 and 83 years) were scanned using B-mode US with the knee flexed at 120°. The range of the angle of probe rotation for the arm was 0-80° and B-mode images (total, 101 images) were acquired every 0.8°. MRI of the knees was also performed using the double echo steady-state sequence. Both US and MRI images were used to create 3-D models of medial femoral condyle articular cartilage. Tc was determined at points 1 mm apart from one another in the US model (Tc-US) and MRI model (Tc-MRI). Tc-US was compared with Tc-MRI and the repeatability of Tc-US was assessed by mean Tc in the specific region of interest of the femoral condyle. Tc-US correlated significantly with Tc-MRI both in volunteers and in OA patients (p < 0.0001 each) and coefficients of correlation were 0.976 and 0.964 for volunteers and OA patients, respectively. The coefficient of variance for mean Tc-US was 4.90%. Our results show that 3-D US measurements of femoral cartilage are reproducible and correlate strongly with MRI measurements.

Effect of low-intensity pulsed ultrasound stimulation on gap healing in a rabbit osteotomy model evaluated by quantitative micro-computed tomography-based cross-sectional moment of inertia

BackgroundIt has been previously demonstrated that low-intensity pulsed ultrasound stimulation (LIPUS) enhances formation of the medullary canal and cortex in a gap-healing model of the tibia in rabbits, shortens the time required for remodeling, and enhances mineralization of the callus. In the current study, the mechanical integrity of these models was confirmed. In order to do this, the cross-sectional moment of inertia (CSMI) obtained from quantitative micro-computed tomography scans was calculated, and a comparison was made with a four-point bending test.MethodsThis parameter can be analyzed in any direction, and three directions were selected in order to adopt an XYZ coordinate (X and Y for bending; Z for torsion).ResultsThe present results demonstrated that LIPUS improved earlier restoration of bending stiffness at the healing site. In addition, LIPUS was effective not only in the ultrasound-irradiated plane, but also in the other two planes.ConclusionsCSMI may provide the structural as well as compositional determinants to assess fracture healing and would be very useful to replace the mechanical testing.

A minute bone bending angle measurement method using echo-tracking for assessment of bone strength in vivo

The purpose of this study is to develop a new ultrasound diagnostic system for non-invasive and quantitative assessment of mechanical properties of the bone or bone healing. In the previous papers, we reported that we had developed a new ultrasound system to measure a minute bone deformation using a multi-point echo-tracking (ET) and that it had a great potential for non-invasive and quantitative diagnosis of bone healing. In this paper, we present a newly developed measurement system with improved accuracy for assessing deformation of intact tibia in vivo. It consists of a dedicated probe, a transmitting/receiving system and analysis software calculating a minute bending angle of the bone surface under a three-point bending (TPB) test. And, we report results of a performance evaluation of the developed system by using test measurements. Furthermore, we evaluated the reproducibility of the in vivo measurement by repeatedly measuring the bending angle of the tibias of 5 healthy volunteers every week for one month. As a result, the evaluation of the accuracy of the measured bending angle using the metallic plate for calibration showed that the standard deviation (SD) of the measurement in range of 0 to 0.1 degrees was 0.004 degrees. Then, we performed an in vivo measurement of normal tibia. The results showed that the mean bending angle of the normal adult tibias under a load of 25 N and a supporting span of the tibial length of each subject was 0.058 degrees with a SD of 0.01 degrees. In addition, SD of the data for the measurement repeatability was 0.006 degrees. We developed a bending angle measurement system for the human tibia using a TPB test and obtained an excellent accuracy of the system and also confirmed through the measurement of the tibia of human volunteers that the repeatability was sufficient to quantitatively assess bending property of the intact tibia.

Control of fracture reduction robot using force/torque measurement

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 patients 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.

Measurement of mechanical properties with respect to gap healing in a rabbit osteotomy model using echo tracking.

The most important issue in the assessment of fracture healing is to acquire information about the restoration of the mechanical integrity of bone. Echo tracking (ET) can noninvasively measure the displacement of a certain point on the bone surface under a load. Echo tracking has been used to assess the bone deformation angle of the fracture healing site. Although this method can be used to evaluate bending stiffness, previous studies have not validated the accuracy of bending stiffness. The purpose of the present study is to ensure the accuracy of bending stiffness as measured by ET. A four-point bending test of the gap-healing model in rabbit tibiae was performed to measure bending stiffness. Echo tracking probes were used to measure stiffness, and the results were compared with results of stiffness measurements performed using laser displacement gauges. The relationship between the stiffness measured by these two devices was completely linear, indicating that the ET method could precisely measure bone stiffness.

Value of Preoperative Analysis Using Three-Dimensional Imaging of LegDeformity after Injury to the Distal Femoral Epiphysis

Background: Assessment of lower extremity alignment is important. The malalignment test is generally assessed two-dimensionally on plain radiographs. In patients with complex deformities, the key points are set inaccurately on Roentgenogram images, leading to problems with both accuracy and reproducibility. Computed tomography (CT) is the current gold standard for evaluating femoral torsion measurements. However, CT images vary depending on slice orientation during scanning, images of flexion deformities are affected by the orientation of the CT slice, making accurate evaluation impossible should a flexion deformity be present. For this reason, three-dimensional preoperative analysis is required. We report a case in which three-dimensional preoperative analysis was used for a patient with leg deformity after injury to the distal femoral epiphysis, with good results. Methods: CT scanning was used to establish a preoperative plan and produced a surface morphology model from CT axial data. Free software was then used to create mirror images of the affected and unaffected sides from these data. The mirror image of the unaffected side was then positioned in three-dimensional space, and vectors were set. The fragment proximal to the osteotomy plane was defined as the reference fragment (RF) and the distal fragment as the corresponding fragment (CF), with the functional axis of the unaffected side forming the helical axis (HA). The amount of deformity correction of the CF required was then calculated automatically in terms of the two parameters of rotation and translation in three dimensions by shifting the CF along the HA. A Taylor spatial frame (TSF) was used to perform gradual correction surgery. Results: The rotational deformity was corrected, a 20-mm medial shift and 12-mm posterior shift persisted. Correction was carried out a second time to correct this deformity. Conclusion: Three-dimensional analysis of long-bone may prove useful for the correction of long bones deformities in the legs when complex deformity is present.