Journal of Gerontology: MEDICAL SCIENCES 2007, Vol. 62A, No. 6, 652–657
Copyright 2007 by The Gerontological Society of America
Hyperkyphotic Posture and Risk of Injurious Falls in Older Persons: The Rancho Bernardo Study Deborah M. Kado,1 Mei-Hua Huang,1 Claude B. Nguyen,2 Elizabeth Barrett-Connor,3 and Gail A. Greendale1 1
Division of Geriatrics, Department of Medicine, David Geffen School of Medicine at University of California, Los Angeles. 2 Medical College of Wisconsin, Milwaukee. 3 Department of Family and Preventive Medicine, School of Medicine, University of California, San Diego.
Objective. Falls among older adults can have serious physical and emotional consequences, ultimately leading to a loss of independence. Improved identification of those at risk for falls could lead to effective interventions. Because hyperkyphotic posture is associated with impaired physical functioning, we hypothesized that kyphosis may also be associated with falls. Methods. Participants were 1883 older adults from the Rancho Bernardo Study. Between 1988 and 1991, kyphosis was measured using a system of 1.7-cm blocks placed under the participants’ heads if they were unable to lie flat without neck hyperextension. Data on falls including injurious falls, demographics, health, and habits were obtained from a selfadministered questionnaire completed at the same visit. Results. Hyperkyphosis was defined as requiring the use of 1 blocks (n ¼ 595, 31.6%). In this cohort, men were more likely to be hyperkyphotic than were women ( p , .0001). Of those who fell, 36.3% were hyperkyphotic, versus 30.2% among those who did not fall ( p ¼ .015). Those who fell were older, more likely to be women, had lower body mass index, did not exercise, did not drink alcohol, and had poor self-reported physical and emotional health. In age- and sex-adjusted models, those with hyperkyphosis were at 1.38-fold increased odds of experiencing an injurious fall (95% confidence interval [CI], 1.05–1.91; p ¼ .02) that increased to 1.48 using a cutoff of 2 blocks versus 1 blocks (95% CI, 1.10–2.00; p ¼ .01). Although women were more likely to fall, after adjustment for possible confounders, men with moderate hyperkyphosis were at greatest fall risk. Conclusions. Moderate hyperkyphotic posture may signify an easily identifiable independent risk factor for injurious falls in older men, with the association being less pronounced in older women.
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ALLS among elderly persons can have serious consequences, both physical and emotional. Falls are also responsible for most fractures, and the risk of falling increases with age (1,2). Other common age-related conditions may amplify the severity of falls, including low bone mineral density, reduced muscle mass, and diminished muscle reflexes (1). Because falls in older persons can ultimately lead to a loss of independence, identifying fall risk factors could have important health implications. One possible risk factor associated with falls is hyperkyphotic or forward leaning posture. Whereas kyphosis is defined as the natural curvature of the thoracic spine, hyperkyphotic posture is an abnormal condition that refers to increased thoracic spine curvature. Hyperkyphotic posture is commonly observed in elderly patients and has been associated with many conditions, including osteoporosis, degenerative joint disease, decreased physical function, impaired pulmonary function, and increased mortality (3–7). Prior research also suggests that hyperkyphotic posture alters fundamental characteristics of balance, which could explain some falls (8–10). A few small studies have yielded conflicting results as to whether hyperkyphosis itself is a fall risk factor (8,11,12). Nonetheless, there is a popular conception that hyperkyphosis does lead to increased falls despite the fact that no studies to date have accounted for possible confounding factors. Given the connection between
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hyperkyphotic posture and loss of physical function, we hypothesized that increased kyphosis would be associated with an increased risk of falls in older persons. To test this hypothesis, we assessed the association between hyperkyphotic posture and self-reported falls (including injurious falls), using data from the Rancho Bernardo Study. We also assessed several potential confounders, including age, sex, bone mineral density, and self-reported health and physical functioning. METHODS
Participants We used data from the Rancho Bernardo Study, a population-based cohort of predominantly white, middle- to upper-middle-class, and relatively well-educated men and women residing in Rancho Bernardo, California. This ongoing study originated in 1972 when 82% of the community-dwelling eligible residents agreed to participate in a survey of heart disease risk factors. Participants were representative of the total community (13). We analyzed data obtained between 1988 and 1992, when 80% of community-dwelling and ambulatory surviving cohort members aged 45–95 years agreed to participate in a study of osteoporosis. The Institutional Review Board of
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Table 1. Kyphosis Measured by Number of Blocks, Stratified by Sex Number of Blocks* 0 1 2 3 4 5 6 7 or more Total
Men 410 105 94 67 33 19 13 11
(54.5%) (13.9%) (12.5%) (8.9%) (4.4%) (2.5%) (1.7%) (1.5%) 752
Women 878 98 88 30 13 11 10 3
(77.6%) (8.7%) (7.8%) (2.7%) (1.1%) (0.9%) (0.9%) (0.3%) 1131
Note: *Occiput-to-table distance was measured in number of 1.7 cm blocks.
the University of California, San Diego, approved the study protocol, and all participants gave written informed consent.
Kyphosis Posture Measurement We used a series of wooden blocks to measure the degree of kyphosis. Hyperkyphotic persons are unable to comfortably rest their head on a flat surface while in the supine position. To measure this phenomenon, we stacked blocks that are 1.7 cm in thickness upon each other and placed them underneath the participant’s head until the participant had a line of sight perpendicular to the plane of the body, without needing to flex or extend the head to lie supine. We defined normal kyphosis as not requiring any blocks to lie in a neutral position; when blocks were required, the participant was defined as having hyperkyphotic posture. This block method has been reported previously in other studies (4–6) and in a sample of 72 men and women aged 65– 90 years. The interrater reliability (assessed by intraclass correlation) of the blocks method was 0.91 (G. Greendale, unpublished data, 2006). Examinations Participants had bone mineral density measured at the total hip, femoral neck, and lumbar spine (L1–L4) using dual-energy x-ray absorptiometry (DXA) (QDR 1000; Hologic, Inc., Waltham, MA) during the baseline osteoporosis visit in 1988–1991. Using a phantom standard, the DXA scanners were calibrated daily and had measurement precisions of 1% for the spine and 1.5% for the hip. Height and weight were measured in participants wearing light clothing without shoes. Body mass index was calculated as weight in kilograms divided by the square of height in meters. Questionnaire Participants completed a self-administered, standardized questionnaire designed to assess lifestyle, demographic, and health information. They provided basic information, including age, sex, level of education (high school or above), tobacco use (current vs past or never), alcohol use (. 12 drinks in the past month), regular exercise (3 times per week), health (both emotional and physical, rated on a scale of 1–5, with 5 indicating very limited health), and
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functional status (stair climbing and walking, assessed by any self-reported difficulty in climbing a flight of stairs or walking 2–3 blocks on level ground). To assess a history of falls, participants were asked if during the past 12 months they had fallen and landed on the floor or ground or had fallen and hit an object such as a table or chair. If they answered ‘‘yes’’ to a history of falling, then they were asked about the number of falls in the past year. They were also asked about injuries resulting from falls that included (i) a broken or fractured bone; (ii) a blow to the head; (iii) sprain or strain; (iv) bruises; (v) bleeding; (vi) other injury; and (vii) no injury.
Statistical Analysis Kyphosis measurement using the blocks method ranged between 0 and 15 blocks. Because few individuals required 3 blocks, we created three different categories of hyperkyphosis for analyses, those with 1 block, 2 blocks, or 3 blocks compared to those with no blocks. Logistic regression analyses were used to determine the odds of either one or more, two or more, or any injurious falls in the past year. Participants’ characteristics were stratified by those who reported one or more falls in the past year versus those who did not. To assess for potential confounders between hyperkyphotic posture and falls, we considered a list of variables thought to be associated with both. We used chi-square or Student’s t tests to test for significant associations between the candidate variable and either kyphotic posture or falls ( p , .10). If the candidate variable met the criteria of association with either falls or kyphotic posture and falls, it was added to the multivariable model, and backward selection ( p , .10) was used to create the final multivariable model. Data were analyzed using the STATA statistical package (version 7.0; College Station, TX). RESULTS We analyzed data from 1883 participants, 60% female, ages 45–98 years. Among these older men and women (mean age 73.6 6 8.9 years for men; 72.7 6 9.0 years for women), hyperkyphotic posture, defined as requiring the use of 1 blocks, was present in 31.6%. Twice as many men were hyperkyphotic (45.5%) as women (22.4%), and there was a consistent trend for a higher proportion of men to be hyperkyphotic at each level of block usage (Table 1). Overall, 24.4% reported one or more falls within the past year; 9.8% reported two or more falls. Of those who fell, 75.4% reported sustaining an injury such as fracture (9.9%), bleeding (13.2%), head trauma (14.7%), sprain (15.8%), and/or bruise (50%). Whereas men were more likely to be hyperkyphotic, women were more likely to fall ( p ¼ .004), and were more than twice as likely as men to sustain an injury if they fell. Participants who reported falls were older (mean age 74.9 years) compared to those without a history of falls (mean age 72.5 years) ( p , .0001). Compared to participants who did not fall, fallers tended to rate their own physical and emotional health more poorly, and reported greater difficulty with walking and climbing, as shown in Table 2. Thirty-six
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Table 2. Study Participant Characteristics, Stratified by History of Falls Variable
No Fallers (N ¼ 1162–1539)
Fallers (N ¼ 370–496)
p Value
430 (30.2) 276 (19.4) 154 (10.8) 72.5 6 8.9 897 (58.3) 986 (84.9) 25.3 6 3.8 0.97 6 0.21 24 (1.9) 425 (32.7) 67 (4.4) 9 (0.6) 925 (71.9) 136 (8.9) 1026 (79.7) 1.66 6 0.81 1.34 6 0.66 95 (7.4) 85 (6.6)
165 (36.3) 116 (25.5) 56 (12.3) 74.9 6 9.3 329 (66.3) 320 (86.5) 24.8 6 3.6 0.96 6 0.21 12 (2.9) 149 (35.4) 32 (6.5) 11 (2.4) 255 (62.2) 39 (7.9) 292 (71.4) 2.00 6 0.96 1.54 6 0.84 57 (13.9) 55 (13.3)
.015 .005 .38 ,.0001 .002 .44 .03 .35 .193 .303 .055 .001 .0002 .50 .0004 ,.0001 ,.0001 ,.0001 ,.0001
1 Blocks, No. (%) 2 Blocks, No. (%) 3 Blocks, No. (%) Age (y), mean 6 SD Female sex, No. (%) Education (. 12 y), No. (%) Body mass index (kg/m2), mean 6 SD Spine bone density (gm/cm2), mean 6 SD Baseline spine fracture, No. (%) Osteoarthritis, No. (%) Stroke, No. (%) Parkinson’s disease (%) Exercise, No. (%) Current smoker, No. (%) Alcohol user (. 12 drinks in past mo), No. (%) Self-reported physical health, mean 6 SD, ranking 1–5: 5 ¼ limited Self-reported emotional health, mean 6 SD, ranking 1–5: 5 ¼ limited Self-reported difficulty climbing, No. (%) Self-reported difficulty walking, No. (%) Notes: Samples sizes vary due to missing values. SD ¼ standard deviation.
1.03–2.00; p ¼ .01–.02). Because men were more likely than women to be hyperkyphotic (potentially signifying postural differences between the sexes with corresponding differences in fall risk), we tested for and found evidence of a significant interaction between kyphotic posture, sex, and injurious falls ( p ¼ .10). Whereas women with hyperkyphotic posture (defined as 1 or 2 blocks) had a 1.5-fold increased odds of reporting a previous injurious fall in the past year, the odds decreased to 1.28–1.30 and were no longer statistically significant after adjustment for age (Table 3). In contrast, men with hyperkyphotic posture defined as 2 blocks retained a significantly increased odds of injurious falls, a risk that persisted after adjusting for age and self-reported health (OR ¼ 1.59, 95% CI, 1.0–2.54; p ¼ .05), age and alcohol use (OR ¼ 1.65, 95% CI, 0.98–2.78; p ¼ .059), or age and any other covariate considered in this analysis (Table 4). Results from the backward selection procedure revealed that with adjustment for age, alcohol use, and selfreported health, the OR decreased by , 10% to 1.47, but the findings were no longer significant ( p ¼ .16), likely due to a loss of power. To determine whether the sex differences could be explained by Parkinson’s disease, we performed other analyses adjusting for or excluding participants with Parkinson’s disease; these adjustments did not materially change the results. In addition, as hyperkyphosis is con-
percent of those who reported falling in the past year had hyperkyphotic posture, versus 30% of those who did not ( p ¼ .015). In crude logistic regression analyses, those with hyperkyphotic posture (1 blocks) were 1.32 times more likely to report a fall in the past year than were those with normal kyphosis (95% confidence interval [CI], 1.05–1.64; p ¼ .015). Using a more rigid criterion of 2 blocks versus 1 block to define hyperkyphotic posture showed an increased odds ratio (OR) of 1.42 (95% CI, 1.11–1.82; p ¼ .005) compared to the original criterion of 1 block. In analyses examining the odds of falling at least once in the past year by 1, 2, or 3 blocks, the ORs ranged from 1.10 for 1 block to 1.69 for 2 blocks to 1.25 for 3 blocks compared to no blocks. Analyses examining the odds of injurious falls revealed similar patterns. The associations between hyperkyphotic posture, defined as either 1 or 2 blocks, and all falls were no longer statistically significant in models adjusted for age or age and sex. In models adjusted for sex only, however, there remained a highly significant association between hyperkyphotic posture (defined as either 1 or 2 blocks) and all falls (OR ¼ 1.47–1.59; 95% CI, 1.16–2.05; p ¼ .001–.0004). In addition, for injurious falls, whether the cutoff definition for hyperkyphotic posture was 1 or 2 blocks, there remained significant associations in age- and sex-adjusted models (OR ¼ 1.38–1.48; 95% CI,
Table 3. Odds of 1 Injurious Fall in the Past Year, Stratified by Sex and Degree of Kyphosis Sex
Hyperkyphotic Posture Definition
Men Women
1 2 1 2
block (n ¼ 342) blocks (n ¼ 237) block (n ¼ 252) blocks (n ¼ 154)
Note: OR ¼ odds ratio; CI ¼ confidence interval.
Crude OR(95% CI), p Value 1.86 2.17 1.50 1.52
(1.22–2.85), (1.42–3.31), (1.08–2.07), (1.03–2.23),
p p p p
¼ ¼ ¼ ¼
.004 .003 .01 .035
Age-Adjusted OR (95% CI), p Value 1.50 1.73 1.30 1.28
(0.96–2.36), (1.10–2.75), (0.92–1.83), (0.85–1.92),
p p p p
¼ ¼ ¼ ¼
.08 .02 .14 .24
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Table 4. Bivariate-Adjusted Models of Hyperkyphotic Posture and Injurious Falls, in Men Only Adjusted for Age þ One Covariate at a Time Alcohol use Self-reported health Body mass index Spine bone density Baseline spine fracture Osteoarthritis Stroke Parkinson’s disease Exercise*,y Current smoking Self-reported emotional health Self-reported difficulty climbing Self-reported difficulty walkingy
1 Block and Injurious Falls OR (95% CI), p Value 1.44 1.41 1.57 1.60 1.46 1.50 1.47 1.46 1.43 1.55 1.44 1.49 1.43
(0.87–2.37), (0.89–2.22), (1.00–2.48), (1.01–2.53), (0.89–2.41), (0.95–2.37), (0.93–2.33), (0.93–2.29), (0.87–2.36), (0.99–2.44), (0.91–2.27), (0.90–2.46), (0.87–2.35),
p p p p p p p p p p p p p
¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼
.16 .14 .05 .05 .14 .08 .10 .11 .16 .06 .12 .12 .16
2 Blocks and Injurious Falls OR (95% CI), p Value 1.65 1.59 1.82 1.93 1.66 1.67 1.72 1.69 1.62 1.78 1.63 1.70 1.63
(0.98–2.78), (1.00–2.54), (1.14–2.90), (1.21–3.10), (0.99–2.80), (1.05–2.68), (1.08–2.75), (1.06–2.68), (0.97–2.73), (1.12–2.82), (1.03–2.60), (1.01–2.87), (0.96–2.75),
p p p p p p p p p p p p p
¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼ ¼
.06 .05 .01 .006 .06 .03 .02 .03 .07 .01 .04 .05 .07
Notes: *Defined as regular exercise three or more times a week. Neither exercise ( p ¼ .24) nor self-reported walking ( p ¼ .82) was significantly associated with injurious falls; they therefore were not considered as confounders. A history of baseline spine fracture was marginally associated with a history of falls ( p ¼ .10). OR ¼ odds ratio; CI ¼ confidence interval. y
sidered a geriatric condition and the original study sample included participants who were as young as 45 years, we conducted other analyses excluding those who were younger than 65 years from the study sample and found no difference in the study results. In analyses of hyperkyphotic posture and multiple falls, the results were significant only in the crude analyses, where the 595 participants who required 1 blocks compared to those who needed no blocks were 1.36 times (95% CI, 1.0–1.87; p ¼ .05) more likely to have reported falling 2 or more times in the past year. These associations were no longer significant after adjustment for age, and there were no other significant findings for multiple falls in other analyses involving hyperkyphotic posture defined as requiring 2 blocks or in sex-stratified models. DISCUSSION In this cohort of older men and women, women were more likely to fall, but men had more hyperkyphosis and hyperkyphotic men were at increased risk of an injurious fall in the past year. In women, the association of hyperkyphosis with falls was not independent of age (ORs ¼ 1.0–1.1) and was not further changed by individual adjustment for other covariates. In contrast, men with hyperkyphosis ( 2 blocks) had significantly increased odds of 1.5–1.7 for injurious falls, even after adjusting for age, or age and any other covariate that was significantly associated with injurious falls. Whether the finding of hyperkyphotic posture in men signifies a truly independent risk factor for injurious falls may be of debate. After simultaneously adjusting for age, alcohol use, and self-reported health, the OR decreased from 1.73 to 1.47 and lost significance ( p ¼ .16); however, because hyperkyphosis itself may lead to poor self-reported health, adjusting for health status may be inappropriate as poor self-reported health is likely to be in the causal pathway leading to falls. Furthermore, even after multivariable
adjustment and concomitant decreased power to detect an effect of hyperkyphosis, the magnitude of the OR decreased by , 10%, demonstrating that, even after accounting for poor health, hyperkyphosis remained an important determinant of injurious falls. The kyphosis OR estimate in predicting injurious falls remained stable no matter which covariates were added to the model (Table 4). If hyperkyphosis is an independent risk factor for falls, its affect on risk may be mediated by posture-induced changes in body mechanics. Lynn and colleagues (9) and Sinaki and colleagues (10) have conducted small comparison studies between women with osteoporosis-related kyphosis and healthy controls, and have demonstrated that those with kyphosis have greater balance abnormalities assessed by computerized dynamic posturography. Specifically, they reported that women with osteoporosis-related kyphosis had greater mediolateral displacement and increased mediolateral velocity compared to controls (10). Lateral spontaneoussway amplitude has been reported to be the single best predictor of future risk of falls (14). In the current study, we did not assess postural dynamics or fall directionality, and therefore are unable to comment if increased lateral postural sway associated with hyperkyphosis could have been a mechanism of increased fall risk in our study population. To our knowledge, this is the first study to show that hyperkyphotic posture increases fall risk to a greater degree in men than in women. Why this should be the case is unclear. It may be that, although older women are much more likely to fall than are older men, with aging the effects of hyperkyphotic posture on fall risk in women become negligible compared to other risk factors such as decreased muscle strength and fear of falling, whereas for men, the finding of hyperkyphotic posture may indicate a degree of frailty or lack of flexibility that is independent of age. Because men are physically stronger than women to begin with, men’s decline in muscle strength with age may not be as strong a risk factor for falls as it is in women. Several
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other observational studies demonstrate that older men tend to be more physically fit than older women (15–18), but they are notably less flexible (19). We also considered whether our findings might be explained by Parkinson’s disease, which is more common in men than in women (20–22). Stooped posture is one of the clinical manifestations of Parkinson’s, and patients with Parkinson’s disease are known to be at increased risk for falls (23). In our study, there were 19 participants (9 men) who reported a diagnosis of Parkinson’s disease. Only 3 of the 10 women with Parkinson’s disease were classified as hyperkyphotic, whereas 89% of the men with Parkinson’s disease were hyperkyphotic. However, adjustment for Parkinson’s disease did not explain the male association of hyperkyphosis with falls, and there was no change in the results after excluding those with self-reported Parkinson’s disease from the analyses. The similar selfreported prevalence of Parkinson’s disease between the sexes in our study may reflect survivor bias in this elderly cohort. Although our results support a sex difference in the association between hyperkyphotic posture and injurious fall risk, sex-specific post hoc power analyses revealed limited power of only 60% to detect a significant association in women. The low power was due to a low representation of women with hyperkyphotic posture. Thus, the finding of hyperkyphotic posture in women may still signify an increased fall risk, but the magnitude of the association does appear to be smaller than that observed for men. We have previously reported sex differences of hyperkyphotic posture in this cohort (4,5). Using the block method that is influenced by cervical as well as thoracic spine curvature, we found that men have twice the prevalence of hyperkyphosis as women, no matter the cutoff used to define it. In a previous study of the same cohort using a radiographic method of the Cobb’s angle to define hyperkyphosis, only 36% of the participants had evidence of underlying vertebral fractures (3). Thus, these study findings challenge the continuing belief that hyperkyphosis is more common in women and results mainly from osteoporosis. When taking into account the cervical spine changes that also contribute to stooped posture, men appear to be more affected, and may suffer from a greater degree of health risks. Our previous studies on hyperkyphotic posture that showed impaired physical function and increased mortality did not reveal significant interactions between sex, hyperkyphotic posture, and either poor physical function or mortality, but it is notable that the mortality rate in men with hyperkyphosis was greater than that for any other subgroup (4). This study had several limitations. First, this was a crosssectional study, so the direction of causality—whether the hyperkyphotic posture causes an increased risk of falls or vice versa—is unclear. The graded dose response speaks against reverse causality, however. Second, we did not collect information on the directionality of falls, and therefore were unable to explore how hyperkyphotic posture might influence the biomechanics of falling. Finally, , 10% of this cohort reported repeated falls, likely to be more meaningful than a single fall for predicting adverse health; we therefore had
inadequate power to assess hyperkyphosis and repeated falls. We were able to demonstrate a significant association between hyperkyphosis and injurious falls, the outcome of clinical consequence. The 75% injury rate for any reported fall points to a plausible selective recall for serious falls, improving the probable validity of this report.
Conclusion Although we have shown that both older men and women with hyperkyphotic posture are more likely to report having any fall or injurious fall in the past year, this association in women appears to be explained by age. In contrast, men with hyperkyphotic posture were at increased risk for sustaining an injurious fall, independent of age and other factors. These results suggest that the simple clinical observation of being unable to lie flat with the head positioned within a margin of 3.4 cm from the examination table could potentially aid in identifying older men at high risk for future injurious falls, so that targeted interventions can be made. These findings deserve confirmation in prospective studies. ACKNOWLEDGMENTS This work was supported by National Institute on Aging grant AG07181 and RO1 AG24246, the Claude D. Pepper Older Americans Independent Center (5P60AG10415-11), and by the American Federation of Aging Research (AFAR) Geriatric Scholars Program.
CORRESPONDENCE Address correspondence to Deborah M. Kado, MD, David Geffen School of Medicine, 10945 Le Conte Ave., Suite 2339, Los Angeles, CA 90095. E-mail:
[email protected]
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Received March 15, 2006 Accepted August 30, 2006 Decision Editor: Luigi Ferrucci, MD, PhD
