Vertebral deformities and fractures are associated with MRI and pQCT measures obtained at the distal tibia and radius of postmenopausal women

SUMMARY

We investigated the association of postmenopausal vertebral deformities and fractures with bone parameters derived from distal extremities using MRI and pQCT. Distal extremity measures showed variable degrees of association with vertebral deformities and fractures, highlighting the systemic nature of postmenopausal bone loss.

INTRODUCTION

Prevalent vertebral deformities and fractures are known to predict incident further fractures. However, the association of distal extremity measures and vertebral deformities in postmenopausal women has not been fully established.

METHODS

This study involved 98 postmenopausal women (age range 60-88 years, mean 70 years) with DXA BMD T-scores at either the hip or spine in the range of -1.5 to -3.5. Wedge, biconcavity, and crush deformities were computed on the basis of spine MRI. Vertebral fractures were assessed using Eastell's criterion. Distal tibia and radius stiffness was computed using MRI-based finite element analysis. BMD at the distal extremities were obtained using pQCT.

RESULTS

Several distal extremity MRI and pQCT measures showed negative association with vertebral deformity on the basis of single parameter correlation (r up to 0.67) and two-parameter regression (r up to 0.76) models involving MRI stiffness and pQCT BMD. Subjects who had at least one prevalent vertebral fracture showed decreased MRI stiffness (up to 17.9 %) and pQCT density (up to 34.2 %) at the distal extremities compared to the non-fracture group. DXA lumbar spine BMD T-score was not associated with vertebral deformities.

CONCLUSIONS

The association between vertebral deformities and distal extremity measures supports the notion of postmenopausal osteoporosis as a systemic phenomenon.

Micro-finite element analysis applied to high-resolution MRI reveals improved bone mechanical competence in the distal femur of female pre-professional dancers

Micro-finite element analysis applied to high-resolution (0.234-mm length scale) MRI reveals greater whole and cancellous bone stiffness, but not greater cortical bone stiffness, in the distal femur of female dancers compared to controls. Greater whole bone stiffness appears to be mediated by cancellous, rather than cortical bone adaptation.

INTRODUCTION

The purpose of this study was to compare bone mechanical competence (stiffness) in the distal femur of female dancers compared to healthy, relatively inactive female controls.

METHODS

This study had institutional review board approval. We recruited nine female modern dancers (25.7±5.8 years, 1.63±0.06 m, 57.1±4.6 kg) and ten relatively inactive, healthy female controls matched for age, height, and weight (32.1±4.8 years, 1.6±0.04 m, 55.8±5.9 kg). We scanned the distal femur using a 7-T MRI scanner and a three-dimensional fast low-angle shot sequence (TR/TE=31 ms/5.1 ms, 0.234 mm×0.234 mm×1 mm, 80 slices). We applied micro-finite element analysis to 10-mm-thick volumes of interest at the distal femoral diaphysis, metaphysis, and epiphysis to compute stiffness and cross-sectional area of whole, cortical, and cancellous bone, as well as cortical thickness. We applied two-tailed t-tests and ANCOVA to compare groups.

RESULTS

Dancers demonstrated greater whole and cancellous bone stiffness and cross-sectional area at all locations (p<0.05). Cortical bone stiffness, cross-sectional area, and thickness did not differ between groups (>0.08). At all locations, the percent of intact whole bone stiffness for cortical bone alone was lower in dancers (p<0.05). Adjustment for cancellous bone cross-sectional area eliminated significant differences in whole bone stiffness between groups (p>0.07), but adjustment for cortical bone cross-sectional area did not (p<0.03).

CONCLUSIONS

Modern dancers have greater whole and cancellous bone stiffness in the distal femur compared to controls. Elevated whole bone stiffness in dancers may be mediated via cancellous, rather than cortical bone adaptation.

Implications of noise and resolution on mechanical properties of trabecular bone estimated by image-based finite-element analysis

Recent advances in micro-magnetic resonance imaging (microMRI) now allow noninvasive assessment of mechanical properties of trabecular bone (TB) in vivo by micro finite-element analysis. The first aim of this work was to address the implications of limited resolution and signal-to-noise ratio on elastic properties of TB derived under conditions of in vivo imaging via simulation at various resolutions and noise levels on the basis of models derived from microCT images at 21 microm isotropic voxel size from cores of cadaveric human TB (n = 13) from three anatomic sites. The second aim was to compare how elastic constants derived from actual MR images at 9.4 Tesla at 50 microm isotropic voxel size compare with those from high-resolution microCT. Elastic moduli computed from simulated in vivo microMR images were highly correlated with those obtained from microCT (R(2) = 0.99) and the data were relatively immune to noise. Correlations of similar strength were obtained between estimated moduli from microCT and acquired high-field MR images. Systematic errors manifesting in significant deviations of the slopes from unity are caused by higher apparent bone-volume fraction of the MR images but can potentially be corrected with appropriate histogram-standardization techniques.