The effects of anti-resorptive therapies and estrogen withdrawal in adult scoliosis measured by sub-segmental vertebral BMD analysis

The sub-segmental analysis of dual energy X-ray absorptiometry (DXA) scans from scoliotic vertebrae has established that there are differences in bone mass between the concave and convex sides of the vertebrae. Furthermore, these differences persisted in patients with low bone mass and were related to the geometry and applied loads, suggesting that this is a good model of bone adaptation in response to external stimuli. The goal of this study was to characterize the response of the human scoliotic spine to anti-resorptive treatments and estrogen withdrawal on the concave and convex sides of the spine. A total of 576 vertebrae (199 no treatment, 214 bisphosphonate, 69 estrogen and 94 estrogen withdrawal) were analyzed from 167 postmenopausal, Caucasian women. An analysis of variance (ANOVA) was used in conjunction with post-hoc Tukey tests to examine the effects of concavity, treatment group, and age. We found that the average change in BMD per year was greater than zero on the concave and convex sides with the exception of the estrogen withdrawal group. Discontinuing estrogen therapy caused patients to maintain bone mass on the concave side, but lose substantial bone density on the convex side. A differential response was also observed with respect to age. Patients younger than 60 exhibited a decrease in total BMD per year concomitant with a small degree of straightening, while those who were 60 or over demonstrated an increase in bone mass and a slight increase in the deformity. Based on these data, it is clear that the differences in BMD between the concave and convex sides of the vertebrae are not simply a result of the deformity, but more likely due to bone accretion. Further study is needed to elucidate the relationship between biomechanical forces and the adaptive response in the spine as a function of time.

The relationship between bone mineral density and biomechanics in patients with osteoporosis and scoliosis

Nearly one-third of all women and one-sixth of all men over age 65 have osteoporosis, and this condition is often accompanied by lumbar scoliosis. Previous work has shown that, in a group of postmenopausal women with scoliosis and osteoporosis, both the bone mineral content (BMC) and bone mineral density (BMD) were greater on the concave side than the convex side. The goal of this study was to examine the structure-function relationships in the spines of patients with low bone mass and scoliosis using a patient-specific biomechanical model. We compared the percent change in BMC and the percent change in BMD with axial force, F(a), shear force, F(s), moment, M, local curvature, theta(rel), and the patient's age, A. We found that the percent change in BMC depended on the applied moment and the local curvature. The same dependence was observed for the percent change in BMD, but in this case, the shear force was also significantly inversely correlated. A population with femoral neck BMD with a T-score greater than -2.0 was similarly evaluated and yielded similar results. The percent change in BMD was related to M, theta(rel), A and negatively to the shear force. These results indicate that the osteoporotic spine is still able to respond to changes in the mechanical environment and provides a useful comparison between patients with osteoporosis and those with normal bone mass. In addition, this model may be a useful tool for the in vivo assessment of bone density changes in response to mechanical stimuli and drug treatments.

Assessment of bone quantity and distribution in adult lumbar scoliosis: new dual-energy x-ray absorptiometry methodology and analysis

STUDY DESIGN

In this study, we elucidated the bone quantity and distribution in lumbar spines of a group of 176 postmenopausal women (average age 72 years) with scoliosis.

SUMMARY OF BACKGROUND DATA

Adolescent idiopathic scoliosis is associated with a low bone mineral density, but the bone mineral density in adult lumbar scoliosis has not been well-characterized.

METHODS

Dual-energy x-ray absorptiometry analysis of the femoral neck and lumbar spines of 176 postmenopausal women were used to assess the bone mineral density and bone mineral content at both anatomic sites. Subsegmental analysis was used to determine the bone distribution within the lumbar vertebrae.

RESULTS

The lumbar spine bone mass was greater than the femoral neck as evidenced by the average lumbar spine and femoral neck T-scores, -0.493 and -1.81, and Z-scores, 1.70 and 0.12, respectively. There was also a significant correlation between the lumbar spine bone mineral density and femoral neck bone mineral density (r2 = 0.24, P < 0.0001). Individual analysis of 655 vertebrae after bisection and trisection showed that the bone mineral density of the concave side was 15% to 20% higher than the convex, and the difference between the 2 sides was at least as great for patients with low femoral neck bone mineral density as those with high femoral neck bone mineral density.

CONCLUSIONS

The quantity and distribution of bone in adult scoliosis is markedly different from adolescent scoliosis. The lumbar spine bone mass is much greater than the femoral neck, and the concave side bone mass is greater than the convex. Finally, subsegmental vertebral dual-energy x-ray absorptiometry analysis may have wider applications in research and clinical settings.