Factors Associated With Kyphosis and Kyphosis Progression in Older Men: The MrOS Study

Hyperkyphosis (HK), or increased anterior curvature of the thoracic spine, is common in older persons. Although it is thought that vertebral fractures are the major cause of HK, only about a third of those with the worst degrees of kyphosis have underlying vertebral fractures. In older men, HK is associated with increased risk of poor physical function, injurious falls, and earlier mortality, but its causes are not well understood. We studied 1092 men from the Osteoporotic Fractures in Men (MrOS) Study aged 64 to 92 years (mean age 72.8 years) who had repeated standardized radiographic measures of Cobb angle of kyphosis to identify risk factors for HK (defined as ≥50 degrees) and kyphosis progression over an interval of 4.7 years. Specifically, we examined the associations with age, body mass index (BMI), weight, weight loss, health behaviors, family history of HK, muscle strength, degenerative disc disease (DDD), bone mineral density (BMD), prevalent thoracic vertebral fractures, and incident thoracic vertebral fractures (longitudinal analyses only). Men had an average baseline kyphosis of 38.9 (standard deviation [SD] 11.4) degrees. Fifteen percent had HK (n = 161) with a mean Cobb angle of 56.7 (SD = 6.0) degrees; these men were older (p < 0.01), had lower BMI (p < 0.01), lower BMD (p < 0.01), were more likely to have family history of HK (p = 0.01), and prevalent thoracic vertebral fracture (p < 0.01) compared with the men without HK. During follow-up, men experienced an average of 1.4 degrees of kyphosis progression with DDD (p = 0.04) and lower hip BMD (p < 0.01) being identified as statistically significant and incident vertebral fractures (p = 0.05) nearly significant factors associated with worse progression. These results suggest that in older men, HK results from not only low BMD and vertebral fractures but that DDD also may play a significant role in kyphosis progression.