Hyperkyphosis Associated With Increased Mortality in Older Women With Vertebral Fractures

Deborah Brauser

June 02, 2009

June 2, 2009 — In older women with previous vertebral fractures, increased kyphosis can predict an increased risk for death, independent of the extent and severity of their underlying spinal osteoporosis, according to the results of a prospective cohort study reported in the May 19 issue of the Annals of Internal Medicine.

"It is well known that vertebral fractures are associated with an increased risk for death in older persons, but the explanation for this is unknown," write Deborah M. Kado, MD, MS, from the MacDonald Research Laboratory in Los Angeles, California, and colleagues. "Our previous work suggested that those with vertebral fractures were more likely to die of a pulmonary cause in particular, possibly because of vertebral fracture–induced changes in the thoracic kyphotic curvature that could detrimentally affect respiratory function."

They note that other studies have suggested that hyperkyphosis itself may be a risk factor for death. However, these studies could not explain whether the increased mortality risk came from increased thoracic curvature or the presence of clinically undetected vertebral fractures.

So Dr. Kado and her team sought to determine whether hyperkyphosis is associated with an increased risk for death independent of vertebral fractures and low bone mineral density. They evaluated a cohort of 610 participants from the Study of Osteoporotic Fractures, an ongoing prospective study of 9704 women 65 years and older recruited from Baltimore, Maryland; the Monongahela Valley, Pennsylvania; Minneapolis, Minnesota; and Portland, Oregon, from 1986 to 1988. Black women and all men were excluded because of the low expected incidence of fractures in these groups.

During the 2-year follow-up visit, 610 women (aged 67 - 93 years), representing all 4 clinic centers, were consecutively sampled to undergo flexicurve measurements to document the degree of thoracic curvature (kyphosis index) and dual-energy x-ray absorptiometry to measure total hip and spine bone mineral density. In addition, prevalent radiographic vertebral factures at baseline were defined by morphometry, and mortality was assessed during an average follow-up of 13.5 years. Also, all study participants completed a baseline questionnaire on education, medical history, and health behaviors, and completed a second visit questionnaire that included cigarette use.

End-of-study results showed that in age-adjusted models, each SD increase in kyphosis carried a 1.14-fold increased risk for death (95% confidence interval [CI], 1.02 - 1.27; P = .023). After adjusting for age and other predictors of mortality (including such osteoporosis-related factors as low bone density, moderate and severe prevalent vertebral fractures, and number of prevalent vertebral fractures), women with greater kyphosis were at increased risk for earlier death (relative hazard per SD increase, 1.15; 95% CI, 1.01 - 1.30; P = .029).

On stratification by prevalent vertebral fracture status, only women with prevalent fractures were at increased mortality risk from hyperkyphosis, independent of age, self-reported health, smoking, spine bone mineral density, number of vertebral fractures, and severe vertebral fractures (relative hazard per SD increase, 1.58; 95% CI, 1.06 - 2.35; P = .024).

"To date, most clinicians and patients attribute their hyperkyphotic posture to underlying osteoporosis; however, our data confirm that postural changes provide important clinical predictive ability that is not provided by markers of osteoporosis alone," write the study authors. "Our results suggest that women with vertebral fractures and hyperkyphosis are at greater risk for death than women with only vertebral fractures or only hyperkyphosis."

Limitations of the study include the participation of white women only, so the findings were not generalizable to men or to nonwhite women. In addition, because the morphometric reading of vertebral fractures was based on vertebral height ratios only, it may have led to misclassification of other causes of decrements in height ratios, such as Scheuermann's disease.

The correlation between kyphotic index and either the kyphotic angle or clinical measures of the distance from occiput to wall was also not known. "So clinically relevant comparisons are difficult to make," write the study authors. "However, each measure has been shown to have construct validity, and the flexicurve measure may even be superior to those that depend on specific vertebral edges, such as the more widely used Cobb angle."

Dr. Kado's team writes that the study also had several strengths. "First, this was a prospective study with substantial long-term and 95% complete follow-up over 13.5 years. Second, all women underwent standardized testing for underlying vertebral fractures; thus, we obviated a limitation of previous studies — inability to exclude underlying vertebral fractures as a mechanism of the association of hyperkyphosis and ill health."

They conclude, "Because it is readily observed and is associated with ill health in older persons, hyperkyphosis should be recognized as a geriatric syndrome — a 'multifactorial health condition that occurs when the accumulated effect of impairments in multiple systems renders a person vulnerable to situational challenges.' "

This study was supported by grants from the National Institute of Arthritis and Musculoskeletal and Skin Diseases and the National Institute on Aging. The study authors have disclosed no relevant financial relationships.

Ann Intern Med. 2009;150:681-687.

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