Postural stability measurement balances technology and treatment

[Guest guest]

Biomechanics Magazine August 2006

Postural stability measurement balances technology and treatment

A dynamic assessment of sway may help practitioners design treatment

for a range of patients.

http://biomech.com/showArticle.jhtml?articleID=192700650

By: Butera

Measuring and evaluating postural stability is an effective way for

practitioners to diagnose balance problems and to decide on treatment

for their patients at risk for falling. New tools for measuring

available data give practitioners a more complete picture of how

their patients move and can help researchers develop new methods for

treating stability issues. This in turn can advance evaluation,

rehabilitation, and performance for people with postural stability

problems.

Continually changing technology is challenging some of the processes

used to provide data for assessing movement. New ways to analyze the

comprehensive data available from testing devices such as the Biodex

Stability System and the NeuroCom International Balance Manager

System are being developed.

The NeuroCom EquiTest system comprises a movable visual surround and

a force plate that can both move backward and forward and rotate. The

system protocol includes the Sensory Organization Test (SOT) and the

Equilibrium Score (ES), a composite of the results of the SOT. The

SOT looks at how proprioception affects postural sway. The ES

averages the weighted scores of a patient's performance under the six

sensory conditions of the SOT, which all take place in the sagittal

plane. It identifies changes of coordination and interaction of the

visual, somatosensory, and vestibular systems that are the focus of

the SOT.

But there are some important balance and stability factors the ES

doesn't consider. The ES assumes a maximum anteroposterior sway angle

of 12.5 degrees before a normal person will fall. But that assumption

doesn't take into account individual differences due to age, sex,

height, or weight. By averaging the single maximum points of anterior

and posterior sway, the ES also can't distinguish between small

amounts of sway in each direction and a large sway angle in one

direction and none in the other. A subject who, say, can control

posterior movement (no sway) but not anterior (large sway angle) is

more likely to fall than someone who moves a little in both

directions-but they may both have the same ES.

A newer measure proposed for use in conjunction with the SOT is the

Postural Stability Index (PSI).1,2 A composite of movements in

several directions, the PSI uses data obtained through the SOT to

augment what can be learned from the ES. The PSI also calculates an

average sway angle. But by incorporating sway across the time of the

trial in the final number, the PSI can give a fuller picture of a

subject's functional balance.

Outcomes and findings

A study to test the efficacy of the PSI was conducted at the

facilities of the VA Medical Center in East Orange, NJ.1 The balance

of 20 subjects, 10 with chronic fatigue syndrome (CFS) and 10 armed

services veterans with no known illness, plus 10 healthy controls was

assessed on the NeuroCom EquiTest system. Prior to testing, none of

the subjects had been diagnosed with any balance problems, though the

CFS patients and vets were chosen because of links between CFS and

balance problems and the fact that the veterans had some of these

symptoms. None took any medications that are known to cause problems

pertaining to balance. Each subject participated in three identical

20-second trials for each of the six conditions. Researchers

calculated ES and PSI outcomes at five-, 10-, and 20-second intervals

to assess how time in the trial would affect final scores. For both

measures, a score of 100 represents perfect stability: the lower a

subject's score (on either measure), the more impaired his or her

balance.

ES and PSI both have a place in the measurement of postural stability

and AP sway but the PSI was created because of a need for deeper

analysis of postural stability. It can offer more practical,

reliable, and valid information for a few reasons.

Clinicians generally accept that ankle stiffness is directly related

to postural stability. The more rigid a patient's ankles, the less

stable the patient. The ES considers the foot and ankle as one unit

with the body swaying above the ankle. The PSI recognizes movement of

the foot independent of the ankle for a more accurate representation

of how ankle stiffness (less independent foot movement) affects

balance. The researchers found that PSI decreased as ankle stiffness

increased, suggesting a negative correlation between ankle stiffness

and postural stability. The ES does not have this capability because

it does not take ankle stiffness (defined as " the rate of change of

torque at the ankle with respect to the displacement (in radians) of

the COM [center of mass] " ) into consideration.2

The study found that a dependable estimate of stability could be

obtained with the PSI even if a subject fell during testing. Because

only the extremes of movement are included, the ES for a subject who

falls is zero for that trial. This is not true with the PSI because

movement through the whole of a trial is considered. In addition, of

2000 data points collected from the SOT, only two values of data for

each trial (maximum anterior sway and maximum posterior sway) are

used to form the ES. The PSI, on the other hand, uses all the data

points plotted by the SOT to measure stability patterns.

The Postural Stability Index is one of many tools that analyze

information gathered from force plate technology and can provide

unique information to the practitioner.

Practical use

A number of patients can benefit from the results of posturography

testing as practitioners can analyze the paths of neurological and

vestibular problems and evaluate existing balance disorders.

According to the American Geriatric Society,3 one-third of the

population in the U.S. over the age of 65 experience unintentional

falls.

" When problems with sluggish reflexes, the sensory system, the

vestibular system, visual changes, and minor weakness occur, there is

an increased chance of a fall, " said Ray Hedenberg, a physical

therapist with South Valley Physical Therapy in Denver. " The EquiTest

gives information about the patient's ability to use sensory systems

and how the information is integrated through the midbrain,

cerebellum, and brain stem and then coordinated with the motor

systems so the patient can respond in an appropriate fashion, " he

said.

Hedenberg works with elderly patients to more effectively use the

vestibular system and try to reactivate and use the function they

have. Posturography systems can look at postural strategies that

patients use to maintain their center of gravity on unstable surfaces.

" That information is particularly helpful with geriatric patients to

help a clinician customize treatment based on assessment findings, "

he said.

The information from the SOT is useful, he said, in determining

whether patients display an appropriate response pattern to maintain

balance under particular conditions.

" If they are using an inappropriate strategy, that puts the patient

at a very high risk for falling, " he said.

Strength and range of motion play a role in effective postural

strategies, as does a patient's cognitive level. Sometimes the

automatic responses of patients with Alzheimer's disease and dementia

can be retrained to safely recruit their muscle groups and sensory

systems and be effective even without full cognitive ability.

More than one million people in the U.S. are living with Parkinson's

disease. Difficulty with balance is one of the symptoms of the

condition.4 With no cure available yet, medication is the best form

of treatment for the neurological disorder.

Researchers at Stanford University Medical Center studied the role of

medication in postural stability for Parkinson's patients in order to

determine which medications and which dosages were most helpful.5

Posturography equipment can help track progress and note changes

medication dosage may have on a patient's tendency to sway. The

researchers used the SOT to gather data on postural sway before and

after patients were medicated. They found a correlation between

medication and tremors.

Sports and sway

Posturography may offer opportunities for evaluating athletic

performance and rehabilitation after injury. Postural stability and

neuropsychological testing are becoming integral parts of

postconcussion assessment in athletes.6 Given that one in five high

school football players sustains a concussion each year and 50% of

college athletes have a history of concussion,7 postconcussion

evaluation is important in determining whether an injured athlete can

return to play. General concussion assessment recommendations of the

Atlantic Coast Conference (ACC) for collegiate sports include general

cognitive and postural stability testing to determine the severity of

concussion. Once an athlete has been assessed postrecovery and

determined to be symptom-free, return to play can be considered.8

Guskiewicz led a recent study on postural stability and

neuropsychological deficits after concussion in college athletes. He

used the SOT to look at postural stability assessment for return to

play. He concluded that the acute balance deficits demonstrated by

athletes with cerebral concussion were likely the result of

ineffective use of information from the vestibular and visual

systems.9 These balance deficits can affect performance and place the

athlete at risk.

Limits of posturography

High equipment costs have so far kept force-plate posturography

technology from making the leap from research facilities to

rehabilitation practices.

" The expense associated with high-tech equipment can be something of

a deterrent to a clinic or a clinician, " Hedenberg said. " That

includes not just NeuroCom equipment, but also isokinetic or motion

analysis equipment. "

Reimbursement is allowable for dynamic posturography and there is an

evaluation code for Medicare, but unfortunately not all insurance

companies follow Medicare's lead.

" With today's reimbursement environment, it is a risk to buy the

systems with high cost because you may not get reimbursed and there

is the worry that you won't be able to pay for it, " Hedenberg

said. " We deal with what we have and utilize our clinical skills.

That's unfortunate but that's the way healthcare is today. "

Advancements in biomechanical devices are changing postural stability

research and evaluation. With new additions like the PSI, data

collection capabilities are evolving. Research will gain from newly

available information and practitioners fortunate enough to have

access to a dynamic posturography equipment system have a richer

assessment tool.

Butera is a freelance writer based in San Francisco with a

BS in kinesiology.

References

1. Chaudhry H, Findley T, Quigley KS, et al. Measures of postural

stability. J Rehabil Res Dev 2004;41(5):713-720.

2. Chaudhry H, Findley T, Quigley KS, et al. Postural stability index

is a more valid measure of stability than equilibrium score. J

Rehabil Res Dev 2005;42(4):547-556.

3. stein LZ. Falls and balance problems. Patient Education

Forum, American Geriatrics Society.

www.americangeriatrics.org/education/forum/falling.shtml, accessed

March 2006.

4. Parkinson's Action Network. About Parkinson's: What is

Parksinson's disease.

www.parkinsonsaction.org/aboutparkinsons/whatisparkinsons.htm,

Accessed June 2006.

5. Bronte- HM, Minn AY, Rodrigues K, et al. Postural

instability in idiopathic Parkinsons disease: the role of medication

and unilateral pallidotomy. Brain 2002;125(Pt 9):2100-2114.

6. Moser RS. Knock Knock: concussions from sports injuries. N J Med

1998;95(11):27-29.

7. Hausdorff JM, Rios DA, Edelberg HK. Gait variability and fall risk

in community-living older adults: a 1-year prospective study. Arch

Phys Med Rehabil 2001;82(8):1050-1056.

8. Guskiewicz KM. Sport-related concussions: Are we headed in the

right direction. The Atlantic Coast Conference (ACC). Sports

Sciences, October Features: Soccer.

www.theacc.com/genrel/100104aac.html, accessed June 2006.

9. Guskiewicz KM, Ross SE, Marshall SW. Postural stability and

neuropsychological deficits after concussion in collegiate athletes.

J Athl Train 2001;36(3):263-273.

---

Test Conditions For Balance Assessment

Eyes open

Surround and platform stable (condition 1)

Surround sway-referenced* (condition 3)

Platform sway-referenced* (condition 4)

Surround and platform sway-referenced* (condition 6)

Eyes closed

Surround and platform stable (condition 2)

Platform sway-referenced* (condition 5)

The platform (in conditions 4,5, and 6) and the surround (in

conditions 3 and 6) are referenced to the subject's self-generated

sway.