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Unipedal stance testing as an indicator of fall risk among older outpatients
Unipedal Stance Testing as an Indicator of Fall Risk Among Older Outpatients Edward A. Hurvitz, MD, James K. Richardson, MD, Robert A. Werner. MD, Anne M. Ruhl, MD, Matthew R. Dixon, MD ABSTRACT. Hurvitz EA, Richardson JK, Werner RA, Ruhl AM, Dixon MR. Unipedal stance testing as an indicator of fall risk among older outpatients. Arch Phys Med Rehabil 2000;8 1: 587-9 I. Objective: To test the hypothesis that a decreased unipedal stance time (UST) is associated with a history of falling among older persons. Design: Fifty-three subjects underwent a standardized history and physical examination and three trials of timed unipedal stance. Setting: The electroneuromyography laboratories of tertiary care VeteransAdministration and university hospitals. Subjects: Ambulatory outpatients 50 years and older referred for electrodiagnostic studies. Outcome Measures: UST and fall histories during the previous year. Results: Twenty subjects (38%) reported falling. Compared with the subjects who had not fallen, those who fell had a significantly shorter UST (9.6 [SD I I .6] vs 31.3 [SD 16.31 seconds, using the longest of the three trials, p < .OOOOl).An abnormal UST (<30sec) was associated with an increased risk of having fallen on univariate analysis and in a regression model (odds ratio 108; 95% confidence interval 3.8, >lOO; p < .007). The sensitivity of an abnormal UST in the regression model was 91% and the specificity 75%. When UST was considered age was not a predictor of a history of falls. Conclusions: UST of <30sec in an older ambulatory outpatient population is associated with a history of falling, while a UST of r30sec is associated with a low risk of falling. Key Words: Accidental falls; Posture; Aging; Equilibrium 0 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation
ALLS ARE A SIGNIFICANT cause of morbidity and F mortality in the elderly.’ It is estimated that approximately one third of persons older than 65 years of age living in the community fall each year.2The economic cost of falls to society is great,3 and the physical and psychological cost to the individual may be even greater. Many who fall are injured,4 but even those who are not injured often do not regain full physical and psychological function.5 Clearly, preventing falls is an important aspect of caring for older patients; however, it is From the Department of Physical Medicine and Rehabilitation, University of Michigan Medical Center. Ann Arbor, MI. Submitted January 25. 1999. Accepted in revised form July 31. 1999. No commercial party having a direct financial interest in Ihe results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to James K. Richardson, MD, University of Michigan Medical Center. Department of Physical Medicine and Rehabilitation, 1500 East Medical Cemer Drive, Room I D204, Ann Arbor. MI 48109-0042. 0 2C00 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation ooO3-9993/00/8105-5439%3.00/O doi: 10.1053/mr.2ooO.6293
difficult to determine which patients are at highest risk for falls and therefore in need of evaluation and intervention. Many strategieshave been used to identify which patients are at greatest risk for a fall. Such strategies often include technology not usually available in the clinical setting,6 detailed history,’ neurologic/musculoskeletal examinations and functional evaluations,E or some combination of tbese.9 Each of these strategies has drawbacks for the busy clinician who often does not have the equipment, expertise, or the time needed to successfullyimplement these techniques.Aquick, easily learned, and reproducible technique that is highly sensitive would be ideal for screening patients for fall risk. In other work, we have found decreased unipedal stance time (UST) to be a sensitive marker of peripheral neuropathy (PN) in older patients (unpublished data). Older subjects with PN have significantly more difficulty maintaining unipedal stance for even 3 seconds compared with age and sex-matched controls, and they demonstrate greater instability during the brief time they are able to balance on one foot.1° More important, we have noted in a small group of older subjects with PN that those with a decreasedUST were significantly more likely to have fallen in the previous year than were those subjects with PN but a greater UST.ll In addition, Studenski and associates’2 found that significantly fewer older subjects with a history of unexplained falls could successfully balance on one foot than similarly aged control subjects without a fall history. Given this background, our primary hypothesis was that a decreased UST would be associatedwith a history of falls among older subjects. In other work, we have correlated UST and PN’O (also unpublished data), as well as PN and a history of faIls.“*‘3 We were concerned that UST might simply identify those subjects with PN (who often fall) and therefore would be equivalent to a careful peripheral neuromuscular examination. Our secondary hypothesis was that UST would identify fallers more effectively than a physical examination designed to detect PN. METHODS Patients The protocol for this study was approved by the review boards of both institutions involved. All patients referred to the electroneuromyography laboratory were assessedfor eligibility for the study. Patients were included if they were: referred for a study of the lower extremities, or for a generalized problem such as peripheral neuropathy or weakness; at least 50 years old; able to ambulate in the community without assistive device; and able and willing to complete the protocol. Patients were excluded from the study if they reported: a history of central nervous system abnormalities; lower extremity musculoskeletal problems (significant arthritis, plantar fasciitis, etc) that might affect unipedal stance; symptoms that might interfere with unipedal stancetesting, such as dizziness,lightheadedness, or pain; or lower extremity amputation. After the study was explained to the subjects, they were questioned about possible significant central necrologic. trauArch
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matic, or arthritic disorders that would exclude them from the study. If all criteria were met, informed consent was obtained. Examinations and Data Collection A standardized history and physical examination was performed. The protocol for this evaluation was adapted from the Michigan Neuropathy Screening Instrument (MNSI) developed by Feldman and colleagues,t4 which provides a standardized history and neurologic examination with a grading scale for the detection and staging of PN. Seven of the 15 questions from the MNSI were used for the clinical history. The other 8 questions were excluded for the sake of brevity and because they lacked relevance to the general population. The physical examination included motor, sensory, and reflex testing. Each area tested was graded from 0 to 2, with higher scores being more abnormal. For motor testing and sensory testing, a score of 0 was normal, a 1 represented decreased function, and a 2 represented no function. For muscle stretch reflex testing, 0 was a normal reflex, 1 was a reflex present only with facilitation, and a 2 represented no reflex. In addition, a history of any falls in the past year was obtained. A fall was defined as an unintentional change in body posture that resulted in the person being on a lower level. Each patient’s unipedal stance was then tested. Patients chose the leg they preferred for the test. They were instructed to keep their legs from touching and to maintain unipedal stance for as long as possible. “Failure” was defined as shifting the stance foot or placing the lifted foot on the floor. The test was stopped and considered normal if the UST reached 45 seconds. Although some investigators have used 30 seconds as a standard,i5 Briggs and associatesI6 believed that a 45-second time limit would reduce any ceiling effect and provide a more normal distribution of times. Subjects were given three trials, unless they achieved 45 secondson the first or second trial. Analysis Responses to clinical history were analyzed individually to determine their correlation with history of falls using 2 X 2 tables. The physical examination scores were analyzed as the total Michigan Diabetic Neuropathy Score (MDNS) and as subsections of that score (motor, sensory, and reflex scores). These values were then compared with falling history using either the Student’s t test or the Kruskal-Wallis test, if there was a difference of variance in the samples. For UST, the longest trial for each patient was analyzed using the Student t test. Normal vs abnormal results on UST were compared with a positive history of falling, using chi square analysis. In addition, the sensitivity and specificity of the ability to maintain unipedal stance for different intervals were determined. Successively lower values for a “normal” UST were used to find the shortest time that would still provide differentiation between fallers and no&hers. All univariate analyses were performed using Epi Info 6.04.” A logistic regression model was created and analyzed using stepwise logistic regression to determine which independent variables correlated best with a positive history of falling in the past year. A similar model was created excluding any information on UST but including the MDNS to compare the two measures and their respective abilities to predict fall history. Similar analyses were performed using multiple falls as the outcome variable. In all analyses, a p < .05 was considered significant and ap 2.05 and C.10 was considered a trend. The analyses were performed with STATA software.r8 Arch
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RESULTS Background Information Fifty-three patients met the criteria for the study. Forty-seven (88.6%) were male. The mean age was 65.7 years (SD = 8.5). Fifty-one percent were referred for electrodiagnostic study on suspicion of a radiculopathy. 43% on suspicion of peripheral neuropathy, and the remainder for other causes. Twenty subjects (38%) reported a fall in the previous year. Fifteen (28% of all subjects. and 75% of those who reported any fall) had a history of multiple falls in the previous year. Patients who reported falls were older than those who did not fall (mean [SD] of 69.8yrs [7.8] vs 63.2yrs [8.0], p < .Ol). History and Physical Examination There were no significant differences in responses to questions relating to peripheral neuropathy between failers and nonfallers. There were, however, differences between failers and nonfallers on the MDNS physical examination scores(table 1). Subjects with a history of falls demonstrated a significantly higher (more abnormal) sensory score than subjects who did not fall (p = .03, using t test.) In addition, the motor score and the total score demonstrated trends toward higher or more abnormal scores (p = .05 and .07, respectively) in the group with a history of falling. Consistent with our previous work, impairments in peripheral neurologic function were associated with a history of falls. Unipedal Stance Data Analyses were performed evaluating the longest UST of the three trials. The average time for the longest trial for all subjects was 23.1 seconds (SD = 18.1). Eighteen subjects (34.0%) achieved a maximum UST of 45 seconds.The average UST for subjects with a history of falling was significantly decreased in comparison with the USTs of subjects without a history of falling (9.6 seconds [SD = 11.61 vs 31.3 [SD = 16.31 seconds, p < .OOOOl[t test]). Analyses were performed with successively lower USTs to determine a threshold that would be clinically useful. Subjects with UST of less than 30 seconds were significantly more likely to report a history of falling than were subjects with UST of 30 seconds or greater (relative risk 11.6; 95% confidence interval [CI] 1.7, 80). Using a UST of 30 seconds as a threshold yielded a sensitivity of 95% and a specificity of 58% (table 2). Logistic regression analysis using the most significant variables, including UST, demonstrated a model that explained 47% of the variability (R2 value of .47; table 3). The same analysis performed while substituting the results of the neurologic examination for the UST results produced a model that explained only 34% of the variability (R* value of .34; table 4). The regression model using UST also demonstrated excellent sensitivity (91%) and fairly good specificity (75%) while the clinical model was lesssensitive (84%) and lessspecific (65%). Age was also a statistically significant predictor of falls in the model with the neurologic examination, with persons of older Table
1: Results
of Clinical
Testing
score TVP~ Total Sensory Motor Reflex Abbreviation: l By ttest.
Average 15.8 6.7 4.5 4.8
(SD)
(10.5) (3.8) (4.3) (4.4)
+Fall 19.2 8.1 5.9 5.3
NS, not significant.
(10.9) (3.4) (5.1) (4.7)
-Fall 13.7 (9.8) 5.8 (3.8) 3.6 (3.5) 4.1 (4.2)
Significance* p= .07 p = .03 p = .05 NS
UNIPEDAL
Table
2: Univariate
UST Parameter
Analyses
of UST
Failers, nl%l
Nonfallers, “I%)
Versus
STANCE
Risk Factors
14 (42.4%)
RR 11.6,95%
z30sec
UST
1 (5%)
19 (57.6%)
80f Negative
9.6 (11.6)
31.3
value, 95%’ p CT .OOOOl
(set)
(16.3)
* Risk of falling with UST of <30sec. ’ Percentage of subjects with UST of z30sec
who
Cl 1.7,
predictive
did not fall.
age more likely to report a fall (p = .02). The odds ratio, however, was close to one with a 95% CI of 1.02 to 1.2. indicating that age was only a weak risk factor. Furthermore, when UST was considered in the model, age was no longer a significant factor related to fall history (p = .33). Some researchers believe that a history of multiple falls is more significant than a single fall.19 Therefore, subjects who had a history of multiple falls were compared with the subjects with no history of falls or only a single fall. Patients with abnormal UST (less than 30 seconds) were found to be at significantly higher risk of having a history of multiple falls (odds ratio 8.5 [95% CI, 1.6 to 601). The sensitivity and specificity of UST with reference to multiple failers was 93% and 50%, respectively. Regression analyses using procedures similar to those described above produced similar results. Abnormal UPS testing was the only variable identified as being a significant predictor of multiple falls, with an odds ratio of 55 (95% CI 2.2, > 100). None of the clinical score variables were identified as predictive of a history of multiple falls. DISCUSSION The major finding is that our primary hypothesis, which proposed that a decreased UST would be associated with falls, was strongly supported. Subjects with a history of falls demonstrated a significantly decreasedmaximal UST over three trials compared with the subjects without a history of falls (9.6 [ 1I.61 and 31.3 [ 16.31 seconds, respectively, p < .OOOOl). Using 30 seconds as a cutoff between “normal” and “abnormal” UST appears useful in that all subjects (but one) who were classified as failers demonstrated an abnormal UST. In addition, only one subject with UST greater than 30 secondshad fallen in the previous year. These data suggest that UST of less than 30 secondswas a sensitive means to identify postural instability of clinical significance in this population. It also suggests that older outpatients with an ability to maintain 30 seconds or more of one-legged stance are at decreasedrisk for falls. A secondary finding is that UST appears to be a more effective means of identifying patients at high risk for a fall than a relatively detailed peripheral neurologic examination. Since peripheral nerve dysfunction has been highly correlated with Table
3: Logistic
Model
Risk Factors for Fall History Abnormal UPS test Numbness Burning in feet History of open sore Pain with walking Age
With
UPS Time, Odds Ratio
589
Hurvitz
4: Logistic
Model
With
Odds Ratio
for Fall History
Clinical
Scores
p Value
95% Cl
Significance
19 (95%)
UST
FALLS,
Table
UST
(SD)
AND
Falls
<30sec
Mean
TESTING
Normal
Versus
Abnormal
p Value
95% Cl
.006 .08
3.8, > 100 .004, 1.4 .04, 1.3
108 .07 .24 11.3 6.4 1.1
Pseudo R2 = .47. Model sensitivity, 75%; model specificity, 91%. False positive rate, 9%; false negative rate, 25%. Positive predictive value, 83%; negative predictive
.I0 .I4 .I5 .33
.45, >I00 .5,81 .94. 1.2
value,
86%.
Age
1.1
Burning in feet Pain with walking
.2 5.5 .2
Temperature Cramps Numbness
sensation
.02 .08 .12
.65,46 .02,2.2 .5,14 .04, 2.3
.I8 .25 .25 .13 44
2.6 .3 1.2 1.1 .94
Motor score Sensory score Reflex score
1.02,1.2 .03, 1.2
.94, 1.6 .85. 1.4 .73. 1.2
.65
Pseudo R2 = .34. Model sensitivity, 65%; model specificity, 84%. False positive rate, 15%; false negative rate, 35%. Positive predictive value, 72%; negative predictive
value,
80%.
falls and reduced UST, it was possible that UST would simply identify those with PN who are already known to be at high risk for a fall. However, regression analysis suggested that UST explained more of the variance associatedwith a history of falls than an examination designed to detect and quantify peripheral neuropathy. This suggeststhat UST does more than just identify neuropathy, but identifies those with or without neuropathy at risk for falls. The relation between UST and falls remained when subjects with multiple falls were compared with the other subjects. This is important, since some researchersbelieve that a history of multiple falls more readily identifies those with an underlying musculoskeletal or neuromuscular disorder.i9 Subject age was a minimally significant predictor of a history of falls when UST was not included, and was no longer relevant when it was included. This suggeststhat an older patient with a normal UST, as defined in this study, is at low risk for a fall. Is it reasonable that UST should so effectively correlate with fall history? Our earlier work i” identified decreased UST as a characteristic of PN, which in turn has been clearly associated with falls.“~i3 It follows that decreased UST would be associated with falls. Furthermore, a decreased UST was found to differentiate failers from nonfallers in a small group of older subjects, all of whom had PN,” and a decreasedUST was found in a small group of older subjects with a history of unexplained falls.i* Decreased UST has also been identified as a predictor of injurious falls among older persons20and falls in general among older men.*i In the latter study, UST was also found to correlate well (r? = .72) with an accepted balance scale.** The biomechanics of gait and balance also suggest that UST should correlate with fall history. Walking might be conceptualized as transiently balancing on one foot and then the other. If this concept is accepted, then UST is an intuitively reasonable test of walking and balancing ability. Walking, however, is better thought of as a controlled fal1.23 A person waIking maintains the center of mass anterior and slightly medial to the base of support. This allows the “fall” to occur forward and slightly toward the swing limb, which then “catches” the center of mass and in turn guides it forward and again slightly medial. With both conceptualizations it is clear that given the shape of the feet, maintaining balance in the frontal plane is of critical importance in preventing a lateral fall. Maintaining balance in the frontal plane requires precise information from the foot and ankle, rapid processing of that information, and rapid adjustment of lower extremity joint torques to compensate for migrations of the center of mass outside of the base of support. Unipedal balance appears to be a convenient way to evaluate these capabilities. Although all subjects but one who fell demonstrated a Arch
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decreased UST and all subjects but one with normal USTs did not fall, a significant number of subjects with a decreased UST did not fall. It is likely that these subjects have some neuromuscular or central neurologic impairment and may be at increased risk for a fall. However, the propensity to fall, and especially to be injured in a fall, is also related to cognitive ability and judgment”; the subjects with a decreasedUST but negative fall history may have a greater ability to compensate for their decreased balance by greater innate caution, intelligence, or both Whatever the reason, the data do not indicate that everyone with a decreased UST is necessarily at high risk for falls. Other clinical measures have been used to determine a patient’s fall risk. Two multi-item scales have been found to be associated with falls8*25;however, these scales take longer to administer than UST, with each including more than 10 separate assessments,and the work demonstrating their association with falls has involved older, frailer subjects as compared with this study. Both of the scales use UST as one of the assessments with 5 and 10 seconds as maximum
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cular and functional status. Assessing one-legged balance provides a quick and simple technique with which to assess overall neuromuscular status and fall risk in ambulatory outpatients older than 50 years of age. The results suggest that in such patients the risk for falls is low for those who have the ability to achieve 30 seconds of balance on one foot on any one of three trials. Inability to maintain unipedal balance for 30 seconds in the same population was commonly, but not universally, associated with a history of falls. The findings therefore suggest that in this population, patients who cannot maintain 30 seconds of unipedal stance deserve a more careful neurologic. musculoskeletal, or functional evaluation and, possibly, intervention to reduce their fall risk.
I.
2. 3. 4. 5. 6. 7. 8. 9. 10. II. 12. 13. 14.
15. 16.
References Gryfe Cl. Amies A, Ashley MJ. A longitudinal study of falls in an elderly population: I. Incidence and morbidity. Age Ageing 1977;6:201-IO. Prudham D, Evans JG. Factors associated with falls in the elderly: a community study. Age Ageing I98 I ; IO: I4 I-6. Alexander BH, Rivara FP, Wolf ME. The cost and frequency of hospitalization for fall-related injuries in older adults. Am J Public Health 1992:82: 1020-3. Tinetti ME. Speechley M, Ginter SF. Risk factors for falls among elderly persons living in the community. N Engl J Med 1988~319: 1701-l. Murphy J, lsaacs B. The post-fall syndrome. Gerontology 1982;28: 265-70. Lord SR, Clark RD. Webster IW. Physiological factors associatedwith falls in an elderly population. J Am Geriatr Sot 1991;39: I l94- 1200. Campbell AJ. Borrie MJ, Spears GE Risk factors for falls in a community-based prospective study of people 70 years and older. J Gerontol 1989;44:M I 12-7. Tinetti ME, Williams FT, Mayewski R. Fall risk index for elderly patients based on number of chronic disabilities. Am J Med 1986:80:429-34. Cutson TM. Falls in the elderly. Am Fam Phys I994;49: 149-56. Richardson JK, Ashton-Miller JA, Lee SG, Jacobs K. Moderate peripheral neuropathy impairs weight transfer and unipedal balance in the elderly. Arch Phys Med Rehabil 1996;77: I 152-6. Richardson JK, Hurvitz EA. Peripheral neuropathy: a true risk factor for falls. J Gerontology: Med Sci 1995;50A:M21 l-5. Studenski S, Duncan PW, Chandler J. Postural responses and effector factors in persons with unexplained falls: results and methodologic issues. J Am Geriatr Sot I991 ;39:229-34. Richardson JK, Ching C, Hurvitz EA. The relationship between electromyographically documented peripheral neuropathy and falls. J Am Geriatr Sot 1992;40:1008-12. Feldman EL, Stevens MJ, Thomas PK. Brown MB, Canal N, Greene DA. A practical two-step quantitative clinical and electrophysiological assessment for the diagnosis and staging of diabetic neuropathy. Diabetes Care 1994; 17: 128 l-9. Bohannon RW, Laskin PA, Cook AC, GearJ, Singer1. Decreasein timed balance test scores with aging. Phys Ther 1984;64: 1067-70. Briggs RC, Gossman MR. Birch R, Drews JE, Shaddeau SA. Balance performance among noninstitutionalizedelderly women.
PhysTher 1989;69:748-56.
17. Epi Info version 6.04. Atlanta (GA): Centers for Disease Control, E$demiology ProgramOffice; 1996. 18. STATA4.0. College Station (TX): Stata Corooration; 1995 19. Nevitt MC, Cumkings SR: K&Id S, Black D. Risk factors for recurrent nonsyncopal falls-a prospective study. JAMA 1989;261: 2663-8. 20. Vellas BJ, Wayne SJ, Romero L, Baumgartner RN. Rubenstein LZ, Garry PJ. One-leg balance is an important predictor of injurious falls in older persons. J Am Geriatr Sot 1997;45:735-8. 21. Vellas BJ, Wayne SJ, Garry PJ, Baumgartner RN. A two-year longitudinal study of falls in 482 community-dwelling elderly adults. J Gerontol Med Sci 1998;53:264-74.
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22. Tinetti ME. Performance-oriented assessment of mobility problems in the elderly. J Am Geriatri Sot 1986;36:613-6. 23. Winter DA. The biomechanics and motor control of human gait: normal, elderly and pathological. 2nd ed. Waterloo, Ontario: University of Waterloo Press; 1991. 24. Tinetti ME, Doucette J, Claus E, Marotolli R. Risk factors for serious injury during falls by community elderly persons. J Am GeriatrSoc 1995;43:1214-21. 25. Berg K, Wood-Dauphinee S, Williams JI, Maki B. Measuring balance in the elderly: validation of an instrument. Can J Public Health 1992;83 Suppl 2:S7-1 I. 26. Podsiadlo D, Richardson S. The timed “up and go:” a test of basic mobility for frail elderly persons. J Am Geriatr Sot 1991;39: 142-8.
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27. Duncan PW, Studenski S. Chandler J, Prescott B. Functional teach: predictive validity in a sample of elderly male veterans. J Gerontol i992;47:M93-8. 28. Wemick-Robinson M, Krebs DE, Giorgetti MM. Functional reach: does it really measure dynamic balance? Arch Phys Med Rehabil 1999;80:262-9. 29. Hayes WC, Myers ER, Norris JN, Gerhart TN, Yett HS, Lipsitz LA. Impact near the hip dominates fracture risk in elderly nursing home residents who fall. Calcif Tissue Int 1993;52:192-8. 30. Cummings SR, Nevitt MC, Kidd S. Forgetting falls-the limited accuracy of recall of falls in the elderly. J Am Geriatr Sot 1988;36:613-6. 31. Vogt TM. Falls, fallacies, and hypertension [editorial]. J Am Geriatr Sot 1995;43: 1169.
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ALLS ARE A SIGNIFICANT cause of morbidity and F mortality in the elderly.’ It is estimated that approximately one third of persons older than 65 years of age living in the community fall each year.2The economic cost of falls to society is great,3 and the physical and psychological cost to the individual may be even greater. Many who fall are injured,4 but even those who are not injured often do not regain full physical and psychological function.5 Clearly, preventing falls is an important aspect of caring for older patients; however, it is From the Department of Physical Medicine and Rehabilitation, University of Michigan Medical Center. Ann Arbor, MI. Submitted January 25. 1999. Accepted in revised form July 31. 1999. No commercial party having a direct financial interest in Ihe results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated. Reprint requests to James K. Richardson, MD, University of Michigan Medical Center. Department of Physical Medicine and Rehabilitation, 1500 East Medical Cemer Drive, Room I D204, Ann Arbor. MI 48109-0042. 0 2C00 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation ooO3-9993/00/8105-5439%3.00/O doi: 10.1053/mr.2ooO.6293
difficult to determine which patients are at highest risk for falls and therefore in need of evaluation and intervention. Many strategieshave been used to identify which patients are at greatest risk for a fall. Such strategies often include technology not usually available in the clinical setting,6 detailed history,’ neurologic/musculoskeletal examinations and functional evaluations,E or some combination of tbese.9 Each of these strategies has drawbacks for the busy clinician who often does not have the equipment, expertise, or the time needed to successfullyimplement these techniques.Aquick, easily learned, and reproducible technique that is highly sensitive would be ideal for screening patients for fall risk. In other work, we have found decreased unipedal stance time (UST) to be a sensitive marker of peripheral neuropathy (PN) in older patients (unpublished data). Older subjects with PN have significantly more difficulty maintaining unipedal stance for even 3 seconds compared with age and sex-matched controls, and they demonstrate greater instability during the brief time they are able to balance on one foot.1° More important, we have noted in a small group of older subjects with PN that those with a decreasedUST were significantly more likely to have fallen in the previous year than were those subjects with PN but a greater UST.ll In addition, Studenski and associates’2 found that significantly fewer older subjects with a history of unexplained falls could successfully balance on one foot than similarly aged control subjects without a fall history. Given this background, our primary hypothesis was that a decreased UST would be associatedwith a history of falls among older subjects. In other work, we have correlated UST and PN’O (also unpublished data), as well as PN and a history of faIls.“*‘3 We were concerned that UST might simply identify those subjects with PN (who often fall) and therefore would be equivalent to a careful peripheral neuromuscular examination. Our secondary hypothesis was that UST would identify fallers more effectively than a physical examination designed to detect PN. METHODS Patients The protocol for this study was approved by the review boards of both institutions involved. All patients referred to the electroneuromyography laboratory were assessedfor eligibility for the study. Patients were included if they were: referred for a study of the lower extremities, or for a generalized problem such as peripheral neuropathy or weakness; at least 50 years old; able to ambulate in the community without assistive device; and able and willing to complete the protocol. Patients were excluded from the study if they reported: a history of central nervous system abnormalities; lower extremity musculoskeletal problems (significant arthritis, plantar fasciitis, etc) that might affect unipedal stance; symptoms that might interfere with unipedal stancetesting, such as dizziness,lightheadedness, or pain; or lower extremity amputation. After the study was explained to the subjects, they were questioned about possible significant central necrologic. trauArch
Phys
Med
Rehabil
Vol81,
May
2000
588
UNIPEDAL
STANCE
TESTING
AND
FALLS,
Hurvitz
matic, or arthritic disorders that would exclude them from the study. If all criteria were met, informed consent was obtained. Examinations and Data Collection A standardized history and physical examination was performed. The protocol for this evaluation was adapted from the Michigan Neuropathy Screening Instrument (MNSI) developed by Feldman and colleagues,t4 which provides a standardized history and neurologic examination with a grading scale for the detection and staging of PN. Seven of the 15 questions from the MNSI were used for the clinical history. The other 8 questions were excluded for the sake of brevity and because they lacked relevance to the general population. The physical examination included motor, sensory, and reflex testing. Each area tested was graded from 0 to 2, with higher scores being more abnormal. For motor testing and sensory testing, a score of 0 was normal, a 1 represented decreased function, and a 2 represented no function. For muscle stretch reflex testing, 0 was a normal reflex, 1 was a reflex present only with facilitation, and a 2 represented no reflex. In addition, a history of any falls in the past year was obtained. A fall was defined as an unintentional change in body posture that resulted in the person being on a lower level. Each patient’s unipedal stance was then tested. Patients chose the leg they preferred for the test. They were instructed to keep their legs from touching and to maintain unipedal stance for as long as possible. “Failure” was defined as shifting the stance foot or placing the lifted foot on the floor. The test was stopped and considered normal if the UST reached 45 seconds. Although some investigators have used 30 seconds as a standard,i5 Briggs and associatesI6 believed that a 45-second time limit would reduce any ceiling effect and provide a more normal distribution of times. Subjects were given three trials, unless they achieved 45 secondson the first or second trial. Analysis Responses to clinical history were analyzed individually to determine their correlation with history of falls using 2 X 2 tables. The physical examination scores were analyzed as the total Michigan Diabetic Neuropathy Score (MDNS) and as subsections of that score (motor, sensory, and reflex scores). These values were then compared with falling history using either the Student’s t test or the Kruskal-Wallis test, if there was a difference of variance in the samples. For UST, the longest trial for each patient was analyzed using the Student t test. Normal vs abnormal results on UST were compared with a positive history of falling, using chi square analysis. In addition, the sensitivity and specificity of the ability to maintain unipedal stance for different intervals were determined. Successively lower values for a “normal” UST were used to find the shortest time that would still provide differentiation between fallers and no&hers. All univariate analyses were performed using Epi Info 6.04.” A logistic regression model was created and analyzed using stepwise logistic regression to determine which independent variables correlated best with a positive history of falling in the past year. A similar model was created excluding any information on UST but including the MDNS to compare the two measures and their respective abilities to predict fall history. Similar analyses were performed using multiple falls as the outcome variable. In all analyses, a p < .05 was considered significant and ap 2.05 and C.10 was considered a trend. The analyses were performed with STATA software.r8 Arch
Phys
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RESULTS Background Information Fifty-three patients met the criteria for the study. Forty-seven (88.6%) were male. The mean age was 65.7 years (SD = 8.5). Fifty-one percent were referred for electrodiagnostic study on suspicion of a radiculopathy. 43% on suspicion of peripheral neuropathy, and the remainder for other causes. Twenty subjects (38%) reported a fall in the previous year. Fifteen (28% of all subjects. and 75% of those who reported any fall) had a history of multiple falls in the previous year. Patients who reported falls were older than those who did not fall (mean [SD] of 69.8yrs [7.8] vs 63.2yrs [8.0], p < .Ol). History and Physical Examination There were no significant differences in responses to questions relating to peripheral neuropathy between failers and nonfallers. There were, however, differences between failers and nonfallers on the MDNS physical examination scores(table 1). Subjects with a history of falls demonstrated a significantly higher (more abnormal) sensory score than subjects who did not fall (p = .03, using t test.) In addition, the motor score and the total score demonstrated trends toward higher or more abnormal scores (p = .05 and .07, respectively) in the group with a history of falling. Consistent with our previous work, impairments in peripheral neurologic function were associated with a history of falls. Unipedal Stance Data Analyses were performed evaluating the longest UST of the three trials. The average time for the longest trial for all subjects was 23.1 seconds (SD = 18.1). Eighteen subjects (34.0%) achieved a maximum UST of 45 seconds.The average UST for subjects with a history of falling was significantly decreased in comparison with the USTs of subjects without a history of falling (9.6 seconds [SD = 11.61 vs 31.3 [SD = 16.31 seconds, p < .OOOOl[t test]). Analyses were performed with successively lower USTs to determine a threshold that would be clinically useful. Subjects with UST of less than 30 seconds were significantly more likely to report a history of falling than were subjects with UST of 30 seconds or greater (relative risk 11.6; 95% confidence interval [CI] 1.7, 80). Using a UST of 30 seconds as a threshold yielded a sensitivity of 95% and a specificity of 58% (table 2). Logistic regression analysis using the most significant variables, including UST, demonstrated a model that explained 47% of the variability (R2 value of .47; table 3). The same analysis performed while substituting the results of the neurologic examination for the UST results produced a model that explained only 34% of the variability (R* value of .34; table 4). The regression model using UST also demonstrated excellent sensitivity (91%) and fairly good specificity (75%) while the clinical model was lesssensitive (84%) and lessspecific (65%). Age was also a statistically significant predictor of falls in the model with the neurologic examination, with persons of older Table
1: Results
of Clinical
Testing
score TVP~ Total Sensory Motor Reflex Abbreviation: l By ttest.
Average 15.8 6.7 4.5 4.8
(SD)
(10.5) (3.8) (4.3) (4.4)
+Fall 19.2 8.1 5.9 5.3
NS, not significant.
(10.9) (3.4) (5.1) (4.7)
-Fall 13.7 (9.8) 5.8 (3.8) 3.6 (3.5) 4.1 (4.2)
Significance* p= .07 p = .03 p = .05 NS
UNIPEDAL
Table
2: Univariate
UST Parameter
Analyses
of UST
Failers, nl%l
Nonfallers, “I%)
Versus
STANCE
Risk Factors
14 (42.4%)
RR 11.6,95%
z30sec
UST
1 (5%)
19 (57.6%)
80f Negative
9.6 (11.6)
31.3
value, 95%’ p CT .OOOOl
(set)
(16.3)
* Risk of falling with UST of <30sec. ’ Percentage of subjects with UST of z30sec
who
Cl 1.7,
predictive
did not fall.
age more likely to report a fall (p = .02). The odds ratio, however, was close to one with a 95% CI of 1.02 to 1.2. indicating that age was only a weak risk factor. Furthermore, when UST was considered in the model, age was no longer a significant factor related to fall history (p = .33). Some researchers believe that a history of multiple falls is more significant than a single fall.19 Therefore, subjects who had a history of multiple falls were compared with the subjects with no history of falls or only a single fall. Patients with abnormal UST (less than 30 seconds) were found to be at significantly higher risk of having a history of multiple falls (odds ratio 8.5 [95% CI, 1.6 to 601). The sensitivity and specificity of UST with reference to multiple failers was 93% and 50%, respectively. Regression analyses using procedures similar to those described above produced similar results. Abnormal UPS testing was the only variable identified as being a significant predictor of multiple falls, with an odds ratio of 55 (95% CI 2.2, > 100). None of the clinical score variables were identified as predictive of a history of multiple falls. DISCUSSION The major finding is that our primary hypothesis, which proposed that a decreased UST would be associated with falls, was strongly supported. Subjects with a history of falls demonstrated a significantly decreasedmaximal UST over three trials compared with the subjects without a history of falls (9.6 [ 1I.61 and 31.3 [ 16.31 seconds, respectively, p < .OOOOl). Using 30 seconds as a cutoff between “normal” and “abnormal” UST appears useful in that all subjects (but one) who were classified as failers demonstrated an abnormal UST. In addition, only one subject with UST greater than 30 secondshad fallen in the previous year. These data suggest that UST of less than 30 secondswas a sensitive means to identify postural instability of clinical significance in this population. It also suggests that older outpatients with an ability to maintain 30 seconds or more of one-legged stance are at decreasedrisk for falls. A secondary finding is that UST appears to be a more effective means of identifying patients at high risk for a fall than a relatively detailed peripheral neurologic examination. Since peripheral nerve dysfunction has been highly correlated with Table
3: Logistic
Model
Risk Factors for Fall History Abnormal UPS test Numbness Burning in feet History of open sore Pain with walking Age
With
UPS Time, Odds Ratio
589
Hurvitz
4: Logistic
Model
With
Odds Ratio
for Fall History
Clinical
Scores
p Value
95% Cl
Significance
19 (95%)
UST
FALLS,
Table
UST
(SD)
AND
Falls
<30sec
Mean
TESTING
Normal
Versus
Abnormal
p Value
95% Cl
.006 .08
3.8, > 100 .004, 1.4 .04, 1.3
108 .07 .24 11.3 6.4 1.1
Pseudo R2 = .47. Model sensitivity, 75%; model specificity, 91%. False positive rate, 9%; false negative rate, 25%. Positive predictive value, 83%; negative predictive
.I0 .I4 .I5 .33
.45, >I00 .5,81 .94. 1.2
value,
86%.
Age
1.1
Burning in feet Pain with walking
.2 5.5 .2
Temperature Cramps Numbness
sensation
.02 .08 .12
.65,46 .02,2.2 .5,14 .04, 2.3
.I8 .25 .25 .13 44
2.6 .3 1.2 1.1 .94
Motor score Sensory score Reflex score
1.02,1.2 .03, 1.2
.94, 1.6 .85. 1.4 .73. 1.2
.65
Pseudo R2 = .34. Model sensitivity, 65%; model specificity, 84%. False positive rate, 15%; false negative rate, 35%. Positive predictive value, 72%; negative predictive
value,
80%.
falls and reduced UST, it was possible that UST would simply identify those with PN who are already known to be at high risk for a fall. However, regression analysis suggested that UST explained more of the variance associatedwith a history of falls than an examination designed to detect and quantify peripheral neuropathy. This suggeststhat UST does more than just identify neuropathy, but identifies those with or without neuropathy at risk for falls. The relation between UST and falls remained when subjects with multiple falls were compared with the other subjects. This is important, since some researchersbelieve that a history of multiple falls more readily identifies those with an underlying musculoskeletal or neuromuscular disorder.i9 Subject age was a minimally significant predictor of a history of falls when UST was not included, and was no longer relevant when it was included. This suggeststhat an older patient with a normal UST, as defined in this study, is at low risk for a fall. Is it reasonable that UST should so effectively correlate with fall history? Our earlier work i” identified decreased UST as a characteristic of PN, which in turn has been clearly associated with falls.“~i3 It follows that decreased UST would be associated with falls. Furthermore, a decreased UST was found to differentiate failers from nonfallers in a small group of older subjects, all of whom had PN,” and a decreasedUST was found in a small group of older subjects with a history of unexplained falls.i* Decreased UST has also been identified as a predictor of injurious falls among older persons20and falls in general among older men.*i In the latter study, UST was also found to correlate well (r? = .72) with an accepted balance scale.** The biomechanics of gait and balance also suggest that UST should correlate with fall history. Walking might be conceptualized as transiently balancing on one foot and then the other. If this concept is accepted, then UST is an intuitively reasonable test of walking and balancing ability. Walking, however, is better thought of as a controlled fal1.23 A person waIking maintains the center of mass anterior and slightly medial to the base of support. This allows the “fall” to occur forward and slightly toward the swing limb, which then “catches” the center of mass and in turn guides it forward and again slightly medial. With both conceptualizations it is clear that given the shape of the feet, maintaining balance in the frontal plane is of critical importance in preventing a lateral fall. Maintaining balance in the frontal plane requires precise information from the foot and ankle, rapid processing of that information, and rapid adjustment of lower extremity joint torques to compensate for migrations of the center of mass outside of the base of support. Unipedal balance appears to be a convenient way to evaluate these capabilities. Although all subjects but one who fell demonstrated a Arch
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decreased UST and all subjects but one with normal USTs did not fall, a significant number of subjects with a decreased UST did not fall. It is likely that these subjects have some neuromuscular or central neurologic impairment and may be at increased risk for a fall. However, the propensity to fall, and especially to be injured in a fall, is also related to cognitive ability and judgment”; the subjects with a decreasedUST but negative fall history may have a greater ability to compensate for their decreased balance by greater innate caution, intelligence, or both Whatever the reason, the data do not indicate that everyone with a decreased UST is necessarily at high risk for falls. Other clinical measures have been used to determine a patient’s fall risk. Two multi-item scales have been found to be associated with falls8*25;however, these scales take longer to administer than UST, with each including more than 10 separate assessments,and the work demonstrating their association with falls has involved older, frailer subjects as compared with this study. Both of the scales use UST as one of the assessments with 5 and 10 seconds as maximum
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AND
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cular and functional status. Assessing one-legged balance provides a quick and simple technique with which to assess overall neuromuscular status and fall risk in ambulatory outpatients older than 50 years of age. The results suggest that in such patients the risk for falls is low for those who have the ability to achieve 30 seconds of balance on one foot on any one of three trials. Inability to maintain unipedal balance for 30 seconds in the same population was commonly, but not universally, associated with a history of falls. The findings therefore suggest that in this population, patients who cannot maintain 30 seconds of unipedal stance deserve a more careful neurologic. musculoskeletal, or functional evaluation and, possibly, intervention to reduce their fall risk.
I.
2. 3. 4. 5. 6. 7. 8. 9. 10. II. 12. 13. 14.
15. 16.
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