This study found that longitudinal increases in kyphosis angle were independently associated with increases in TUG times. To the knowledge of the authors, this is the first study to suggest the presence of an independent association between kyphosis and mobility in longitudinal analysis. It showed that changes in kyphosis are correlated with concurrent changes in mobility, strengthening the evidence for a causal link. Accounting for the increase in mobility in the fully adjusted model, TUG performance times were 0.02 seconds (95% confidence interval (CI) =0.01–0.03 seconds) longer for every 5° increase in kyphosis angle, more than the increase in mobility time of 0.01 seconds (95% CI =0.005–0.03) over 1 year observed in this cohort. These effects were small in magnitude but clearly independent of other known correlates of impaired mobility, including age, self-reported poor health, grip strength, BMD, and history of vertebral fractures. Furthermore, these effects would likely accrue given more time or after an intervention.
Although baseline kyphosis and change in kyphosis were significantly associated with worsening mobility in age-adjusted models, the association with change remained significant and was twice as strong in the fully adjusted model. Thus, worsening kyphosis may be a more-sensitive marker of increasing impairment than any single kyphosis measurement. Kyphosis increased by 3.9 ± 8.6° in this cohort over 4 years, more than the 1.7° increase over 10 years observed in men and women aged 50 years old at baseline without vertebral fractures10
but less than the 5.6 ± 0.7° increase over 3 years reported in postmenopausal women with a recent vertebral fracture.9
The current cohort had TUG performance times of 9.6 ± 2.7 seconds at baseline, comparable with those of other age-matched cohorts,25
and the 0.70 ± 2.0-second increase in TUG observed over 4 years in the current study was comparable with the increase in TUG reported by able-bodied adults who transitioned to disabled over 2 years.26
Furthermore, for every new vertebral fracture over the 4.4 years of this study, TUG performance increased 0.40 seconds (95% CI =0.24–0.55), more than the increase in performance time from baseline or increasing kyphosis. Thus, the increasing kyphosis and worsening TUG observed might indicate an underlying decline in physical status that could be clinically important.
A recent consensus report aimed at preventing or delaying functional decline and disability in frail older people recommended targeting treatments at all of the impairments that increase risk of frailty.27
The current data suggest that increasing kyphosis predicts longer TUG, thus increasing the risk for falls, functional decline, disability, and frailty. Although age, health status, grip strength, BMI, change in hip BMD, and new vertebral fractures are associated with longer mobility time, increasing kyphosis is a significant factor that should also be considered when developing interventions aimed at preventing functional decline. Increasing kyphosis may be part of an aging syndrome associated with bone loss, fractures, and muscle weakness leading to decline in mobility, but it is important to recognize that greater kyphosis can be easily clinically identified and that effective treatments that reduce kyphosis are available.13,15,17,28
Further work is needed to identify the specific mechanisms involved in increasing kyphosis and to determine whether attenuating the expected age-related rise in level of kyphosis can slow mobility decline.