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Patients with rheumatoid arthritis can lose a substantial amount of vertebral strength over relatively short periods of time, making them vulnerable to severe osteoporosis unless they receive treatment, according to a report in November's Arthritis & Rheumatism.
Japanese researchers, led by Dr. Taro Mawatari at Kyushu University in Fukuoka, used a technique known as finite element analysis of clinical resolution 3-dimensional quantitative computed tomography to study 30 women with rheumatoid arthritis and no radiologic signs of L3 compression fractures. The women were randomized either to treatment with alendronate, 5 mg per day, or to a control group that didn't receive any antiresorptive treatment.
The finite element analysis technique, the authors explain, integrates the 3-dimensional geometry and density information contained in the CT scan into a biomechanical model. The model gives "excellent noninvasive estimates of vertebral strength and has been shown to differentiate postmenopausal women with prevalent fractures from those without fractures, when measurement of vertebral aereal bone mineral density could not."
For their current study, the investigators modified the model to yield clues to the effect of alendronate on the relative strength contribution of the trabecular and cortical compartments.
After an average of 12.2 months, there was a median decrease of 10.6% in vertebral strength in the control group but no significant change in the alendronate group. "Strength decreased more rapidly within the trabecular bone, and alendronate treatment was much more effective in the peripheral than the trabecular compartment," the authors report.
"Cadaver studies have demonstrated that vertebral compression strength generally decreases by 12% per decade throughout adulthood," they point out. "Our finding that the rheumatoid arthritis patients who did not receive antiresorptive treatment lost, on average, 10% strength in only 1 year is therefore equivalent to an 8-fold acceleration of aging effects in terms of loss of bone strength."
They continue, "This provides a plausible mechanistic explanation for the high fracture risk in rheumatoid arthritis, particularly when the disease is treated with corticosteroids. The results also explain why alendronate helps to reduce fracture rates in this population, since alendronate treatment completely arrested this loss of strength."
Monitoring their patients only with traditional dual x-ray absorptiometry (DXA) studies could have misidentified gains or losses in strength, because results of bone density studies were only weakly correlated with changes in strength as estimated by finite element analysis of the CT scans, the authors write.
"The substantial magnitude of the finite element-predicted 1-year loss of vertebral strength in the rheumatoid arthritis patients in this cohort, and its arrest by treatment with alendronate, suggest that rheumatoid patients may develop severe osteoporosis if not treated to alleviate this strength loss," the team concludes.
Arthritis Rheum 2008;58:3340-3349
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