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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 61:866-870 (2006)
© 2006 The Gerontological Society of America

Foot and Ankle Risk Factors for Falls in Older People: A Prospective Study

Hylton B. Menz, Meg E. Morris and Stephen R. Lord

1 Musculoskeletal Research Centre, Faculty of Health Sciences, La Trobe University, Bundoora, Victoria, Australia.
2 School of Physiotherapy, University of Melbourne, Parkville, Victoria, Australia.
3 Prince of Wales Medical Research Institute, University of New South Wales, Randwick, Australia.

Address correspondence to Hylton B. Menz, PhD, NHMRC Australian Clinical Research Fellow, Musculoskeletal Research Centre, School of Physiotherapy, Faculty of Health Sciences, La Trobe University, Bundoora, Victoria 3086, Australia. E-mail: h.menz{at}latrobe.edu.au


   Abstract
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 Abstract
Methods
 Results
 Discussion
 References
 
Background. Foot problems are common in older people and are associated with impaired balance and functional ability. Few prospective studies, however, have been undertaken to determine whether foot problems are a risk factor for falls.

Methods. One hundred seventy-six people (56 men and 120 women, mean age 80.1, standard deviation 6.4 years) residing in a retirement village underwent tests of foot and ankle characteristics (including foot posture, range of motion, strength, and deformity) and physiological falls risk factors (including vision, sensation, strength, reaction time, and balance) and were followed for 12 months to determine the incidence of falls.

Results. Seventy-one participants (41%) reported falling during the follow-up period. Compared to those who did not fall, fallers exhibited decreased ankle flexibility, more severe hallux valgus deformity, decreased plantar tactile sensitivity, and decreased toe plantarflexor strength; they were also more likely to have disabling foot pain. Discriminant function analysis revealed that decreased toe plantarflexor strength and disabling foot pain were significantly and independently associated with falls after accounting for physiological falls risk factors and age.

Conclusions. Foot and ankle problems increase the risk of falls in older people. Interventions to address these factors may hold some promise as a falls prevention strategy.

FOOT problems are reported by approximately 30% of community-dwelling older people (1–4), and are associated with reduced walking speed (1) and difficulty performing activities of daily living (1,4,5). There is also emerging evidence that foot problems may impair balance in older people. A cross-sectional study of 135 older people demonstrated that an overall measure of foot impairment based on the observation of foot lesions and structural deformities was independently associated with performance on clinical tests of balance and functional ability (6). More recently, we reported that ankle flexibility, plantar tactile sensitivity, and toe plantarflexor strength were significant and independent predictors of balance and functional test performance, explaining up to 59% of the variance in these measures (7).

Several studies have suggested that foot problems may be a risk factor for falls. Four retrospective studies (4,8–10) have shown that older people who suffer from foot problems are more likely to have fallen in the previous 12 months. Prospective data to confirm this association are limited, however. In a prospective study of 100 men aged 65–85 years, Gabell and colleagues (11) reported that undefined "foot problems" were associated with a 4-fold increased risk of falling; however, people with disabling foot conditions were excluded and no adjustment for confounders was undertaken. Tinetti and colleagues (12) found that the presence of a "serious foot problem" (defined as a moderate to severe bunion, toe deformity, ulcer, or deformed nail) doubled the risk of falling in 336 people older than 75 years. A prospective study of 979 people older than 70 years in Finland found that those with bunions were twice as likely to fall than were those without (13). More recently, a study of musculoskeletal pain in 1002 women older than 65 years found that the foot was the only pain site that was significantly associated with an increased risk of falling (14).

The major limitation of the evidence pertaining to foot problems and falls is the lack of standard definitions and assessments of foot conditions. Furthermore, a range of foot and ankle characteristics that may not be considered to be "foot problems"—such as foot posture, range of motion (ROM), and strength—have been shown to be associated with balance (7,15) but have not yet been evaluated as potential falls risk factors in a prospective study. Therefore, the aim of this investigation was to examine whether a range of standardized tests of foot and ankle characteristics previously shown to be associated with impaired balance are also risk factors for falls in older people.


   METHODS
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 Abstract
 Methods
Results
 Discussion
 References
 
Participants
The study sample comprised 176 people (56 men and 120 women) aged 62–96 years (mean 80.1, standard deviation = 6.4) who were residing in a retirement village (Table 1). Recruitment was via a mail-out to all residents. Residents were deemed ineligible for the study if they were unable to ambulate household distances without an assistive device or if they scored <7 on the Short Portable Mental Status Questionnaire (16). The participation rate was 54%. Age and sex data were available for nonresponders. Non-responders were of similar age (mean 80.1, standard deviation = 7.3) and sex (38% men) to participants. The Human Ethics Committee at La Trobe University approved the study, and written informed consent was obtained from all participants.


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  		Table 1. Self-Reported Prevalence of Major Medical Conditions, Medication Use, Participation in Physical Activity, and Mobility and Activities of Daily Living (ADL) Limitations in the Study Population.

 
Foot and Ankle Characteristics
Foot and ankle characteristics were tested across six domains: foot posture, foot ROM, foot deformity and lesions, foot strength, foot sensation, and foot pain. Foot posture was assessed using the foot posture index, arch index, and navicular height (17). Navicular height was corrected for differences in foot size by dividing it by the length of the foot. Ankle flexibility was measured in degrees using a modified version of the weight-bearing lunge test (18). First metatarsophalangeal joint (1st MPJ) ROM was measured in a non-weight-bearing position with a goniometer while the examiner maximally extended the hallux (19). The presence and severity of hallux valgus was determined using the Manchester scale (20). An overall measure of hallux valgus severity was determined by summing the scores for right and left feet. Presence of lesser digital deformity, corns, and calluses was determined (18), and a sum of the total number of each of these abnormalities for both feet was documented. The strength of the plantarflexor muscles of the hallux and lesser toes was determined using the paper grip test (21). Tactile sensitivity of the 1st MPJ was evaluated with an aesthesiometer using a two-alternative forced choice protocol (18). Foot pain was assessed using the case definition of the Manchester Foot Pain and Disability Index (MFPDI), which required participants to have current pain, to have pain lasting for at least 1 month, and to report at least one of the items on the MFPDI questionnaire (22). Reliability coefficients for each of the foot and ankle tests when administered to older people are as follows: foot posture index, 0.61; arch index, 0.99; navicular height, 0.64; ankle flexibility, 0.87; 1st MPJ ROM, 0.85; Manchester scale for hallux valgus, 0.77; paper grip test, 0.65; 1st MPJ tactile sensitivity, 0.70 (18).

Physiological Falls Risk
Participants' falls risk was assessed using the Physiological Profile Assessment (PPA) (23). Based on performance in five physiological domains, the PPA computes a fall risk score (standardized score) for each individual; this measure has a 75% predictive accuracy for falls in older people (24,25). Falls risk scores below 0 indicate a low risk of falling, scores between 0 and 1 indicate a mild risk of falling, scores between 1 and 2 indicate a moderate risk of falling, and scores above 2 indicate a high risk of falling. The tests from the short form PPA assessment are described in Table 2.


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  		Table 2. Physiological Profile Assessment (PPA) Short Form Assessment.

 
Falls Ascertainment
Participants were followed for 1 year to determine the incidence of falls. Falls were defined as events that resulted in a person coming to rest unintentionally on the ground or other lower level, not as the result of a major intrinsic event or overwhelming hazard. Participants were provided with monthly calendars to document falls, and a standardized postfall interview was conducted as soon as possible following each fall. Falls reports were also cross-referenced with those collated by the village nurse. Participants were then classified as fallers (those who fell at least once during the follow-up period) or nonfallers (those who did not fall). Participants who fell but did not complete the entire 12-month follow-up were included in the analysis as fallers. One participant died soon after commencement of the study and was excluded from the analysis.

Statistical Analysis
Variables with right-skewed distributions were log transformed. Differences in foot and ankle characteristics and physiological falls risk scores between fallers and nonfallers were assessed using independent samples t tests (for continuously scored variables), Mann–Whitney U tests (for nonparametric variables), or chi-square tests (for dichotomous variables). Variables found to significantly differ between nonfallers and fallers were then entered into two separate discriminant function analyses to determine their relative importance in discriminating between the two groups. The first analysis involved entering the foot and ankle variables in isolation using the enter method. The second analysis used the stepwise method, with foot and ankle variables, physiological risk factor scores, and age included. After deriving each discriminant function, cross-validation was carried out using the jackknife procedure. The data were analyzed using SPSS for Windows (SPSS, Inc., Chicago, IL).


   RESULTS
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 Methods
 Results
Discussion
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Falls
Of the 175 participants included in the follow-up analysis, 71 (41%) fell at least once during the 12-month follow-up period. Fallers were significantly older than nonfallers (81.4 ± 6.4 vs 79.1 ± 6.3 years, t173 = –2.32, p =.022). There were no differences in the prevalence of major medical conditions between the two groups.

Foot and Ankle Characteristics
Foot and ankle characteristics for nonfallers and fallers are shown in Table 3. There were no differences between the groups for any of the foot posture variables, 1st MPJ ROM, or the number of corns, calluses, or lesser toe deformities. However, fallers exhibited reduced ankle flexibility, more severe hallux valgus deformity, reduced tactile sensitivity, and were more likely to fail the paper grip test of the lesser toes and to have disabling foot pain than nonfallers.


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  		Table 3. Foot and Ankle Characteristics in Nonfallers and Fallers.

 
Physiological Falls Risk
Physiological falls risk scores ranged from –1.47 to 5.17, indicating that participants' levels of risk ranged from very low to very high. Fallers exhibited significantly higher physiological falls risk scores compared to nonfallers (1.23 ± 1.51 vs 0.67 ± 1.20; t173 = –2.70, p =.008).

Discriminant Function Analysis
The discriminant function analyses are presented in Table 4. The first discriminant model, in which only the foot and ankle variables were considered, revealed that disabling foot pain, the paper grip test of the lesser toes, tactile sensitivity of the 1st MPJ, ankle flexibility, and hallux valgus severity were significantly and independently associated with falls. The second discriminant model, in which foot and ankle variables, physiological risk factor scores, and age were entered in a stepwise manner, revealed that only the paper grip test of the lesser toes and disabling foot pain were independently associated with falls. The classification accuracy of the two models was similar.


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  		Table 4. Results of Discriminant Function Analyses.

 

   DISCUSSION
Top
 Abstract
 Methods
 Results
 Discussion
References
 
The aim of this study was to determine whether a series of tests of foot and ankle characteristics are associated with falls in older people. Compared to nonfallers, fallers exhibited reduced ankle flexibility, more severe hallux valgus deformity, and reduced plantar tactile sensitivity. Fallers were also more likely to have weak toe plantarflexor muscles, and had a higher prevalence of disabling foot pain. Interestingly, many of the foot and ankle variables found to differ between fallers and nonfallers were also found to be independent predictors of balance and functional ability in our cross-sectional analysis of the baseline data (7), which suggests that the increased risk associated with these characteristics is mediated by reduced balance and reduced ability to perform functional tasks. Two of these foot and ankle characteristics (toe plantarflexor weakness and disabling foot pain) remained significantly and independently associated with falls after including age and physiological falls risk in the discriminant function model.

The observation of reduced ankle flexibility in fallers is consistent with two previous retrospective studies (26,27). Reduced ankle dorsiflexion may increase risk of falling by impairing balance and the ability to perform functional tests integral to daily living. Mecagni and colleagues (15) found significant associations between ankle ROM and Performance-Oriented Mobility Assessment and functional reach scores. Similarly, our analysis of baseline data revealed ankle flexibility to be an independent predictor of postural sway, leaning balance, alternate stepping, sit to stand, and walking speed (7).

Hallux valgus was found to be more pronounced in fallers than in nonfallers. This finding is consistent with those of Koski and colleagues (13), who found that the presence of an undefined "bunion" was associated with a 2-fold increased risk of falls. We have previously shown that hallux valgus impairs balance (7) and that older people with moderate to severe hallux valgus demonstrate less rhythmic movements of the upper body when walking on uneven ground (28), which may contribute to falls. Similarly, reduced tactile sensation was evident in fallers, consistent with previous prospective studies (24,25) and investigations reporting associations between sensory loss and impaired balance (7,29).

An interesting finding was the higher prevalence of toe plantarflexor weakness in fallers. Although age-related reductions in toe plantarflexor strength have been previously reported (30), to our knowledge the association between toe weakness and falls is a novel finding. The toes appear to play an important role in stabilizing the body when the center of mass is displaced in both standing and walking; therefore, the reduced grasping ability of the toes may contribute to loss of balance and falls. In our analysis of the baseline data, we found reduced toe strength to be a significant independent predictor of balance tasks involving forward leaning, an alternate stepping test, and sit to stand (7).

The strengths of this study are the use of clearly defined, validated measures of foot and ankle characteristics and the inclusion of a well-established physiological falls risk score in the multivariate model. It is acknowledged, however, that the study has certain limitations. First, the participants were recruited from a retirement village, and the results may not be generalizable to a more active community-dwelling population. Indeed, the falling rate (41%) is considerably higher than the 30% rate commonly reported in community samples. Second, we used a simple faller versus nonfaller comparison as the study was not sufficiently powered to evaluate differences between once-only and multiple fallers, which may explain the relatively low classification accuracy of the discriminant function model.

These findings have implications for falls prevention, as the identified risk factors are potentially modifiable. Ankle flexibility may be increased with stretching (31), Tai Chi (32), and water exercise (33) programs. Similarly, preliminary evidence suggests that "grasping" exercises to strengthen the muscles of the toes results in improved standing balance in older people (34). Reduction in foot pain is associated with improved functional ability (35), and surgical realignment of hallux valgus deformity has been shown to normalize the loading patterns under the hallux (36), which may improve gait stability (28). Finally, there is emerging evidence that augmenting tactile sensory information from the sole of the foot by the use of insoles with raised projections improves responses to perturbation (37). The efficacy of each of these interventions in reducing falls warrants further investigation.

Conclusion
This study provides prospective evidence that foot and ankle characteristics—particularly reduced ankle flexibility, hallux valgus deformity, decreased tactile sensitivity, decreased toe plantarflexor strength, and foot pain—are important risk factors for falls in older people. Intervention strategies to address these modifiable risk factors may be beneficial in reducing falls.


   Acknowledgments
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This study was supported by an RM Gibson Fellowship from the Australian Association of Gerontology and by the NHMRC Health Research Partnerships Grant: Prevention of Injuries in Older People.

Dr. Menz is currently NHMRC Australian Clinical Research Fellow (id: 234424).

We thank Michael Smythe (Manager) and Margaret Smythe (Director of Nursing) of the La Trobe Retirement Village for their assistance.


   Footnotes
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 Discussion
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Decision Editor: Luigi Ferrucci, MD, PhD

Received September 29, 2005

Accepted February 12, 2006


   References
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