J Bone Miner Res 2006 (Mar); 21 (3): 419—423 ~ FULL TEXT
Huang MH, Barrett-Connor E, Greendale GA, Kado DM
Division of Geriatrics,
Department of Medicine,
David Geffen School of Medicine at University of California,
Los Angeles, California 90095, USA
It is unknown whether kyphosis of the thoracic spine is an independent risk factor for future osteoporotic fractures. In 596 community-dwelling women, we found that with increasing kyphosis, there was a significant trend of increasing fracture risk that was independent of previous history of fractures or BMD (bone mineral density).
INTRODUCTION: It is unknown whether kyphosis of the thoracic spine is an independent risk factor for future osteoporotic fractures.
MATERIALS AND METHODS: We conducted a prospective cohort study of 596 community-dwelling women, 47–92 years of age. Between 1988 and 1991, BMD of the hip and spine and kyphosis were measured. Kyphosis was measured by counting the number of 1.7–cm blocks necessary to place under the occiput so participants could lie flat without neck hyperextension. New fractures were reported over an average follow-up of 4 years.
RESULTS: Using a cut-off of at least one block, 18% of the participants had hyperkyphotic posture (range, one to nine blocks). There were 107 women who reported at least one new fracture (hip, spine, wrist, clavicle, shoulder, arm, hand, rib, pelvis, leg, or ankle). In logistic regression analyses, older women with hyperkyphotic posture (defined as at least one block) had a 1.7–fold increased risk of having a future fracture independent of age, prior fracture, and spine or hip BMD (95% CI: 1.00–2.97; p = 0.049). There was a significant trend of increasing fracture risk with increasing number of blocks, with ORs ranging from 1.5 to 2.6 as the number of blocks increased from one to at least three blocks compared with those with zero blocks (trend p = 0.03; models adjusted for age, baseline fracture, spine or hip BMD). Stratification by baseline fracture status and controlling for other possible confounders or past year falls did not change the results.
CONCLUSION: Whereas hyperkyphosis may often result from vertebral fractures, our study findings suggest that hyperkyphotic posture itself may be an important risk factor for future fractures, independent of low BMD or fracture history.
From the FULL TEXT Article:
HYPERKYPHOSIS, OR EXAGGERATED forward thoracic curvature, is often equated with osteoporosis because vertebral fractures are assumed to be a major causative factor. However, recent evidence suggests that hyperkyphosis itself is an important clinical entity and that up to one-half of those with clinical complications seen in the setting of severe hyperkyphosis have no evidence of underlying vertebral fractures. [1, 2] Known complications from hyperkyphosis include poor respiratory function, [3–5] compromised physical function, [6–8] and increased mortality. 
Whereas not all studies of hyperkyphosis and various adverse health outcomes have measures of underlying vertebral fractures, those that did have shown that the kyphotic deformity itself may have important clinical implications. For example, in the article by Leech et al,  the correlation between the Cobb's angle of kyphosis and reduced pulmonary function was stronger than the effect of the sum of the number of vertebral fractures. With regards to studies on poor physical function, in a small study of postmenopausal women, those who were more kyphotic had worse physical fitness, and only 2 of 35 women had mild radiographic vertebral deformities.  In the Rancho Bernardo study, we previously showed that hyperkyphotic posture was strongly associated with worse self-reported and performance-based physical function independent of clinical spine fractures. 
It is well established that prior osteoporotic fractures are a strong risk factor for future fractures,  but it is unknown whether hyperkyphosis itself is also a risk factor for osteoporotic fracture. We tested the hypothesis that hyperkyphosis is associated with an increased risk for future fractures, unexplained by osteoporosis. We studied participants from the Rancho Bernardo Study who had BMD and kyphosis measured between 1988 and 1991, and we ascertained the number of new clinical fractures that occurred over an average follow-up of 4 years.
In this cohort of community-dwelling, ambulatory, older women, modest hyperkyphosis predicted an increased risk of fracture over the next 4 years, independent of age, history of previous fracture, spine or hip BMD, body mass index, and lifestyle. There are at least two plausible reasons why hyperkyphotic posture might be associated with an increased risk of future osteoporotic fractures. The first is that hyperkyphotic posture is a good surrogate marker for underlying osteoporosis. Previous studies have shown that hyperkyphotic persons tend to have lower BMD, [14, 15] and it is well accepted that vertebral fractures can cause hyperkyphosis. A second reason hyperkyphotic posture might be associated with an increased risk of future osteoporotic fractures may be that hyperkyphosis alters balance,  leading to falls and subsequent fracture. Our previous research suggests that hyperkyphosis measured by the block method can adversely affect both self-reported and measured physical function,  and it is known that poor physical function is a risk factor for falls. 
We studied both mechanisms and found that neither completely explained the kyphosis-fracture association. Analyses adjusted for BMD and baseline fractures, and stratified analyses excluding those with any baseline fracture, did not materially change the results. Furthermore, the subpopulation with hyperkyphosis and no morphometric vertebral fracture at the follow-up visit still retained a 1.7–fold increased risk of future clinical fracture. Additional evidence that hyperkyphosis is not simply a marker of underlying osteoporosis comes from an earlier paper from the Rancho Bernardo cohort showing that a radiographic measurement of kyphosis was not associated with radiographic thoracic vertebral fractures in the majority of older women (63%).  In this study, a history of falls did not explain the association between hyperkyphotic posture and new fractures. Thus, hyperkyphosis seems to be an aging-related phenotype related not only to osteoporosis, but also other physiologic processes.
We suggest that hyperkyphosis may be a potential marker of accelerated aging, with fracture risk increasing not only with chronological age, but also with increasing kyphosis based on increasing number of blocks (Table 3). It is remarkable that such a small increment of 1.7 cm (equals one block) could have such strong clinical implications. Inability to lie flat without neck hyperextension is a good clinical marker of increased fracture risk. That this is a clinically important association is supported by previous reports from the cohort that persons who are unable to lie flat are at increased risk of poor physical function and earlier mortality. [8, 9]
Other researchers have also suggested that postural changes in the absence of osteoporosis have clinical importance and that women with hyperkyphosis and no known vertebral fractures suffer from worse health than those without hyperkyphosis even if they have underlying spine fractures. [18, 19] One study of 140 older women with chronic low back pain reported that functional limitations and quality-of-life measures were similarly impaired in those with spine deformation whether or not there were underlying vertebral fractures.  In another study of 756 women 31–89 years of age, women who reported a previous fracture without associated postural changes did not differ from those without prior fractures, but those that had no fractures and a height loss of >5 cm or kyphosis had significantly more physical difficulty.  Although the numbers were small in our study, only those with previously reported spine fractures and hyperkyphosis, as opposed to just a history of spine fracture, experienced a subsequent fracture. Thus, hyperkyphosis, regardless of its causes, is a clinically important finding.
Previous studies have found vertebral fractures to be a particularly strong risk factor for future fractures. [11–13] This study raises the possibility that it is not just the vertebral fracture, but the postural changes, that are driving the increased fracture risk. To our knowledge, no previous studies have accounted for how postural changes might affect the risk between spine fractures and future osteoporotic fractures.
Study limitations should be noted. The majority of spine fractures are subclinical and are undiagnosed, and we did not have spine X-rays at baseline. However, we were able to ascertain the presence of prevalent vertebral fractures at the follow-up visit and showed that the study results were unchanged even after excluding those with later radiographic evidence of a vertebral fracture. Second, although diagnostic detection bias could have increased the diagnosis of spine fractures in women who had hyperkyphosis, the amount of the kyphosis was small, as was the number of reported clinical spine fractures. Furthermore, only one-half of the women with reported spine fractures had kyphosis by the block method. Finally, whereas we were able to control for a history of falls at baseline, we did not assess falls during the 4–year follow-up. This would not have changed the observed association, but could show a mechanism whereby falls associated with forward posture explain fracture risk.
The strength of this study is the well-characterized community-dwelling cohort of older women unselected for hyperkyphosis or osteoporosis, making it more generalizable than previous studies of patients. If confirmed, the simple block measure of kyphosis could be easily applied for clinical use. The results allow clinicians to draw attention to the potential importance of very small changes in posture.
In summary, older women with modest hyperkyphotic posture are at increased risk of developing clinical fractures, independent of a history of fractures. These results remained after excluding participants who had radiographically detected vertebral fractures. We suggest that small changes in forward posture deserve clinical attention. Application of this method would suggest those patients who are unable to lie flat on the examining table without neck hyperextension should be evaluated for spine fractures, because spine fractures are an indication for treatment to prevent additional fractures. Whether and how to treat women with hyperkyphosis without fractures is unclear and deserves further study.