The contribution of trabecular bone structure to bone strength is of considerable interest in the study of osteoporosis and other disorders characterized by changes in the skeletal system. Magnetic resonance (MR) imaging of trabecular bone has emerged as a promising technique for assessing trabecular bone structure. In this in vitro study we compare the measures of trabecular structure obtained using MR imaging and higher-resolution X-ray tomographic microscopy (XTM) imaging of cubes from human distal radii. The XTM image resolution is similar to that obtained from histomorphometric sections (18 microns isotropic), while the MR images are obtained at a resolution comparable to that achievable in vivo (156 x 156 x 300 microns). Standard histomorphometric measures, such as trabecular bone area fraction (synonymous with BV/TV), trabecular width, trabecular spacing and trabecular number, texture-related measures and three-dimensional connectivity (first Betti number/volume) of the trabecular network have been derived from these images. The variation in these parameters as a function of resolution, and the relationship between the structural parameters, bone mineral density and the elastic modulus are also examined. In MR images, because the resolution is comparable to the trabecular dimensions, partial volume effects occur, which complicate the segmentation of the image into bone and marrow phases. Using a standardized thresholding criterion for all images we find that there is an overestimation of trabecular bone area fraction (approximately 3 times), trabecular width (approximately 3 times), fractal dimension (approximately 1.4 times) and first Betti number/ volume (approximately 10 times), and an underestimation of trabecular spacing (approximately 1.6 times) in the MR images compared with the 18-microns XTM images. However, even for a factor of 9 difference in spatial resolution, the differences in the morphological trabecular structure measures ranged from a factor of 1.4 to 3.0. We have found that trabecular width, area fraction, number, fractal dimension and Betti number/volume measured from the XTM and MR images increases, while trabecular spacing decreases, as the bone mineral density and elastic modulus increase. A preliminary bivariate analysis showed that in addition to bone mineral density alone, the Betti number, trabecular number and spacing contributed to the prediction of the elastic modulus. This preliminary study indicates that measures of trabecular bone structure using MR imaging may play a role in the study of osteoporosis.

Purpose: To quantify normal, in vivo tibio‐femoral knee joint kinematics in multiple weight bearing positions using non‐invasive, high‐resolution MRI and discuss the potential of developing future kinematic methods to assess patients with abnormal joint pathologies. Methods: Ten volunteers with clinically normal knees pushed inferiorly on the footplate of a weight bearing apparatus inside the MR scanner. The volunteers held the weight (133 N) for five scans as the knee motion was evaluated from 0° to 60° of flexion. Full extension was set as the zero point for all measured parameters. Using 3D reconstructions, tibia motion relative to the femur and flexion angle was measured as varus–valgus angle, axial rotation, anterior–posterior translation, and medial–lateral translation. Medial and lateral compartment tibio‐femoral contact areas were examined and centroids of the contract areas were calculated. Results: Tibial internal rotation averaged 4.8° at 40° of flexion and then decreased. Tibial valgus increased by 8° at 60° of flexion. Femoral roll back also increased to 18.5 mm average at 60° of flexion, while the tibia translated medially 2.5 mm. Medial compartment femoro‐tibial contact area started at 374 mm2 and decreased to 308 mm2 with flexion of 60°, while lateral compartment contact area did not change significantly from 276 mm2. Conclusions: Results correlate with previous studies of knee kinematics while providing greater three‐dimensional detail. MR imaging allows excellent non‐invasive evaluation of knee joint kinematics with weight bearing. This tool may potentially be used for assessing knee kinematics in patients with knee pathology. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.

Recently, basic fibroblast growth factor (bFGF) has been found to increase trabecular bone mass and connectivity in the proximal tibial metaphyses (PTM) in osteopenic rats. The purpose of this study was to determine the bone anabolic effects of bFGF in the lumbar vertebral body (LVB), a less loaded skeletal site with a lower rate of bone turnover than the PTM. Six-month old female Sprague-Dawley rats were ovariectomized (OVX) or sham-operated and untreated for 8 weeks to induce osteopenia. Then group 1 (sham) and group 2 (OVX) were treated subcutaneously (s.c.) with vehicle, and OVXed groups 3 and 4 were treated s.c. with PTH [hPTH (1-34) at 40 microg/kg, 5x/week] and bFGF (1 mg/kg, 5x/week), respectively, for 8 weeks. At sacrifice, the fifth LVB was removed, subjected to micro-CT for determination of trabecular bone structure and then processed for histomorphometry to assess bone turnover. The sixth LVB was used for mechanical compression testing (MTS, Bionix 858). The data were analyzed with the Kruskal-Wallis test followed by post-hoc testing as needed. After 16 weeks of estrogen deficiency, there were significant reductions in vertebral trabecular bone volume and trabecular thickness. Treatment with either bFGF or hPTH (1-34) increased BV/TV in OVX animals. Human PTH (1-34)-treated animals had significant increases in trabecular (48%) and cortical thickness (30%) and bone strength [maximum load (53%) and work to failure (175%)] compared to OVX + Vehicle animals. Treatment of osteopenic rats with bFGF increased bone volume (15%), trabecular thickness (13%), maximum load (45%) and work to failure (140%) compared to OVX + Vehicle animals (all P <0.05). Basic FGF increased trabecular bone volume in the lumbar vertebral body of osteopenic rats by restoring trabecular number, thickness and connectivity density. Also, bFGF improved bone mechanical properties (maximum force and work to failure) compared to the OVX + Vehicle group. Therefore, increasing the number, thickness and connections of the trabeculae contributes to increased bone strength in this small animal model of osteoporosis.

This study evaluated the effect of Cenestin, a synthetic conjugated estrogens product, on the maintenance of trabecular bone microarchitecture, bone strength, and of bone turnover in the ovariectomized (ovx) rat model. Two doses of Cenestin were chosen in an attempt to approximate the equivalent human oral doses of 0.3 mg and 0.625 mg. Forty-nine 6-month-old retired female breeder Sprague-Dawley rats were randomly assigned to one of four groups: (1) sham-operated + vehicle; (2) ovx + vehicle; (3) ovx + day 1 post-ovariectomy Cenestin (8.12 mg/kg); (4) ovx + day 1 post-ovariectomy Cenestin (16.24 mg/kg) for 8 weeks. Trabecular structure of the right proximal tibia of each rat was imaged noninvasively by microCT. A compression test to induce a tibial plateau fracture was performed to determine the mechanical properties of the proximal tibia. Urine was collected on days 0, 14, 28, 42 and 56 and serum on days 0, 28 and 56 to assess biochemical markers of bone turnover including deoxypyridinoline crosslinks and osteocalcin. Both biochemical markers of bone turnover were analyzed by ELISA. Trabecular bone mass, structure, and connectivity density in the Cenestin-treated groups did not differ statistically ( p>0.05) from those of the sham-operated + vehicle-treated rats, but all were significantly higher ( p<0.05) than in the ovx + vehicle-treated rats. Structure Model Index, a measure of trabecular plate morphometry, in Cenestin-treated rats maintained a more equal mix of plate- and rod-like structures similar to the sham group, whereas the ovx group had predominantly rod-like trabeculae. Fracture load in the Cenestin (16.24 mg/kg) treated group was 31% ( p<0.01) higher than in the sham + vehicle-treated group and 61% ( p<0.05) higher than in the ovx + vehicle-treated group. Both the sham-operated + vehicle-treated and Cenestin-treated groups showed significantly lower urinary deoxypyridinoline crosslink excretion at all timepoints and serum osteocalcin at day 56 compared with the ovx + vehicle-treated group. In summary, Cenestin maintained trabecular bone microarchitecture and strength in an ovariectomized rat model of estrogen deficiency.

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