Osteopenia in adolescent idiopathic scoliosis. A primary problem or secondary to the spinal deformity?

STUDY DESIGN: A cross-sectional study to assess the lumbar spinal and proximal femoral bone mineral density in girls aged 12, 13, or 14 years with adolescent idiopathic scoliosis and to compare them with bone mineral densities of an age-matched control group.

OBJECTIVES: To determine whether there is an association of osteopenia with idiopathic scoliosis, to compare bone mineral density in patients with scoliosis in different age groups with healthy controls, and to correlate bone mineral density with scoliotic parameters, including the pattern and magnitude of the curve.

SUMMARY OF BACKGROUND DATA: Routine radiographs allow very limited assessment of osteopenia. Therefore, only a few studies have compared osteopenia in patients with scoliosis with that in healthy individuals. New techniques allow a more reliable quantification of the bone mineral state in adolescent idiopathic scoliosis. Available series in the literature either had a small sample population with inadequate controls or examined a large age range.

METHODS: Using a dual energy x-ray absorptiometer, bone mineral density was measured in the predominant trabecular bone area, i.e., the lumbar spine (L2-L4) and bilateral proximal femur, in 81 girls aged 12, 13, or 14 years old with idiopathic scoliosis of various degrees of severity. Results were compared with those of 220 age-matched healthy control girls.

RESULTS: In all three age groups, scoliotic patients had significantly lower bone mineral density in all measured regions than that in the control individuals (student's t test). Sixty-eight percent of the scoliotic individuals had a significantly reduced bone mineral density. Differences in bone mineral density between bilateral hips (paired t test) were not statistically significant either in scoliotic patients or in healthy control individuals. No differences in body weight, body height, or menarche status were found between the scoliotic and control individuals. Correlation studies showed that, in scoliotic patients, the values of bone mineral density did not correlate with the curve degree or curve pattern.

CONCLUSIONS: There is a persistently lower bone mineral density in patients between 12 years and 14 years of age with idiopathic scoliosis. The decreased bone mineral density occurred in patients with idiopathic scoliosis before the age of 12 years, with no further progression from the age 12 to age 14, and did not correlate with the scoliosis degree or pattern. These findings suggest that the osteopenia in idiopathic scoliosis may be related to the primary etiology of the disease rather than secondary to the asymmetrical mechanical forces associated with the back deformities.