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Halo Vest Effect on Balance James K. Richardson, MD, Alan D. Marr Ross, MD, Barth Riley, PhD, Robert L. Rhodes, MPA, CO ABSTRACT. Richardson JK. Ross ADM. Riley B. Rhodes RL. Halo vest effect on balance. Arch Phys Med Rehabil 2000;8 I :255-7. Objective: To determine the effect of a halo vest. a cervical orthosis. on clinically relevant balance parameters. Design: Subjects performed unipedal stance (with eyes open and closed. on both tirm and soft surfaces) and functional reach. with and without the application of a halo vest. Subjects: A convenience sample of I2 healthy young subjects, with an equal number of men and women. Outcome Measures: Seconds for unipedal stance (maximum 45): inches for functional reach. Results: Both unipedal stance times and functional reach (mean -C standard deviation) were significantly decreased with the halo vest as compared to without it (29.1 ? 5.8 vs 32.8 -t 6.4 seconds,/> = ,002: 12.9 2 I .4 vs 15.1 2 2.1 inches. p < .Ol). Conclusion: A halo vest causes an acute impairment in balance in the healthy young. It is likely that the impairment would be greater in older or injured patients. thus increasing their risk for a fall, which could have devastating consequences. Key Words: Orthotic devices; Equilibrium; Posture; Proprioception: Rehabilitation. 0 2000 by the American Cmgress cine rind the Arnericm Academy Rehabilitation

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T HAS BEEN OUR clinical observation that a halo vest, Ideleterious commonly used to stabilize high cervical fractures.’ has a effect on balance; however. little has been written on the effect of cervical orthoses on balance. What work has been done suggests that cervical orthoses have no clinically relevant effect on balance. Burl and colleagues’ found that a cervical collar had no acute effect on standing balance as determined by force plate sway velocity. Karlburg and associates3 also found that a cervical collar had no acute effect on balance or eye movements in young healthy subjects; however, after 5 days of using the collar subjects demonstrated decreased velocity of voluntary saccades and subtle deterioration in anterior-posterior body sway induced by vibration at the calf muscles. The authors concluded that “restriction of cervical movement only marginally affects postural control.“’ Despite these somewhat equivocal studies,there is experimental and theoretical evidence that links cervical structures and balance. It has been reported that trauma to the second cervical roots leads to disordered balance,” and that cervical radiculopaFrom the Department of Physical Medicine and Rehabiliration. Universily of Michigan Medical Center, Ann Arbor. Ml. Dr. Ross is currently afliliated with fhe Department of Medicine, Augusla Campus. Main General Hospital. Augusla. ME. Submilted for publicalion January 25. 1999. Accepted in revised form June 9. 1999. No commercial party having B direct financial interest in Ihe results of the research supporting this article has or will confer a benefil upon the authors or upon any organization with which the authors are assocked. Reprint requests to James K. Richardson. MD. Assislanl Professor. Department of Physical Medicine and Rehabilitation. 1500 E. Medical Crnkr Drive. Ann Arbor. Ml 48 1094042. 0 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation OGO3-9993/00/8103-5440%3.OO/O

thy impairs performance on posturography. which then improves after surgical decompression.s There is evidence that neck muscle proprioceptors are used by higher cortical structures to determine body orientation in space6 and have a significant effect on control of eye movements in patients with unilateral labyrinthine dysfunction.’ Unilateral local anesthesia of the upper posterior cervical roots leads to nystagmus8 and ataxia in animals.’ Similar anesthesia in humans produces increased ipsilateral extensor tone and disordered gait.‘O Some believe that lesions in the upper cervical regions lead to a “cervical vertigo.” but this remains controversial.” If such a syndrome does exist, Brandt suggeststhat “restraining cervical mobility by rigid neck collars” is one possible model.” Given our clinical observations and the apparent relation between cervical muscle proprioception and postural control, we hypothesized that a halo vest would impair high-level balance activities. More specifically, we hypothesized that a halo vest would acutely impair the ability of young healthy subjectsto maintain unipedal stanceand perform a functional reach. METHODS Subjects. Twelve healthy young subjects (ages 24 to 38) who were all free of neuromuscular and musculoskeletal diseasewere recruited for the study. There were equal numbers of men and women. Halo vest application. A 4-inch cotton stockinet was placed over the subject’s head to cover potential pin sites. Three to four layers of 2-inch Soft Cast,* a fiberglass molding material, were then wrapped around the subject’s head to cover pin sites; excess stockinet inferior to the Soft Cast was then trimmed away. A Bremmer halo crownb was then applied using the recommended protocol. Pin modification was also necessary. The crown was secured on the early subjects by reducing the point of the pin by approximately one third. Later subjects used pins recently designed for pediatric use; these were felt to be more comfortable and were associated with less erythema when removed. The pins were applied to a finger tightness that was comfortable to the subject; experience showed this to be 1 to 2 foot-lbs of torque. The vest and superstructure were then applied with the subject in the supine position. The halo vest did not interfere with shoulder flexion, retraction, or protraction. Measurements. The subjects performed unipedal balance under eight different conditions. The conditions included eyes open on a hard and soft surface, and eyes closed on a hard and soft surface. The soft surface was a 15-cm thick foam mat. These four conditions were performed with and without the halo vest in place. One half the subjects underwent testing without the halo first, while the other half were tested initially in the halo vest. For unipedal balance testing, the subjects were asked to stand with their arms folded across their chest on the foot of their choice for as long as possible. Failure was defined as touching the floor with the nonstance foot, unfolding the arms, or hopping/shifting on the stance foot. The test continued for a maximum of 45 seconds. Each subject was given three opportunities under each condition. The subjects’ functional reach was also measured, again with and without the halo vest. Functional reach was determined as Arch

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has been described.i* Briefly, a yardstick was fixed to a wall at shoulder height. The subjects then stood comfortably and flexed their shoulder forward 90” with the elbow fully extended so that the arm was parallel to the floor. The distance to the distal third digit was recorded. The subject then reached forward as far as possible without losing balance or taking a step, and the distance to the distal third digit was again recorded. The difference between the two measures was determined and recorded as the subject’s functional reach. Subjects performed a practice trial and then one trial for measurement, with and without a halo vest applied. Statistical analysis. The unipedal stance times were analyzed using each subject’s best time of the three trials in each condition, and also the average of the three trials in each condition. When using the best times in each condition analyses of covariance were used to control for differing numbers of trials acrossvarious conditions. When using the average time in each condition, a two-tailed t test was performed unless the data were non-normative, in which case the Wilcoxon signed rank test was used. The functional reach data were also analyzed using a paired. two-tailed t test. Statistical significance was set at p < .05. RESULTS Unipedal Stance Ties All of the subjects were able to achieve the maximum unipedal stance time of 45 seconds with eyes open, whether on a firm or soft surface, with or without the halo vest. When the average of the subjects’ three trials under each condition were analyzed, unipedal stance times were significantly decreased with the halo as compared to without (mean + SD, 29.1 + 5.8 set vs 32.8 2 6.4 set, respectively; p = .002) and on the soft surface as compared to the firm (26.6 + 6.0 set vs 35.3 5 7.1 set, respectively; p < .OOl). The eyes-open data for unipedal stance were not normally distributed; however, the difference between unipedal stance times with the eyes closed as compared to open was still significant by the Wilcoxon signed rank test (18.3 ? 10.4sec vs 43.7 ? 2.3sec, respectively; Z(12) = -3.06,~ = .002; table 1). Analyses of covariance using each subject’s best time in each condition demonstrated that the subjects’ unipedal stance times were significantly decreased in the halo vest as compared to without it across the two floor type conditions (p < .OS).In addition, unipedal stance times were significantly decreased with eyes closed as compared with eyes open (p < .05). However, unipedal stance time was not significantly decreased as a function of halo status or floor type across all conditions (table 2). Table

1: Measurements Under

Unipedal Halo Halo Eyes Eyes

Stance vest on vest off closed open

of Unipedal Stance and Various Conditions

Firm surface Functional Reach Halo vest on Halo vest off

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(seconds) 29.1 f 32.8 -t 18.2 2 43.7 2 26.6 + 35.3 +-

Soft surface

Results

Functional

5.8 6.4 10.4

t = 3.991,

2.3 6.0 7.1

Z= t=

-3.061, 5.281,

(inches) 12.9 + 1.4 15.1 2 2.1 as mean

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p < .Ol

p = .002

p =

.002

p < .OOl

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Table 2: Subjects’ Conditions: Analysis Condition Halo on vs off

Eyes closed Soft floor l

vs open vs firm

Best Unipedal of Covariance

Stance Times Under Various Controlling for Number of Trials

F: Halo On/Off

E Condition

t? Halo y Condition

1.42 .04

6.67*

6.67*

6.00*

.47

.47

p < .05.

Functional Reach Distances The subjects demonstrated a significantly decreasedfunctional reach with as compared to without the halo vest (I 2.9 + I .4 vs 15.1 ? 2.1 inches,respectively;p < .Ol; table 1). DISCUSSION The major finding of this study was that healthy young subjects demonstrated a decrease in both unipedal stance time and functional reach with a halo vest compared to without one. To our knowledge this is the first time that a cervical orthotic has been found to have an acute effect on clinically relevant balance parameters. The only other study that found a cervical orthotic affected balance suggested that the effect was subtle and became evident only after 5 days of continuous orthotic use.3 Although we found a clear impairment in balance with the acute use of a halo vest, our study may underestimate the real impact of a halo vest on postural stability. Given that a halo vest is usually worn for 3 to 4 months, the impact on balance may be much greater in clinical practice. Furthermore, many patients who require a halo vest may have had a period of bed rest, a myelopathy, or other neurologic or orthopedic trauma that will impair balance further. Therefore, the decrement in balance we found in healthy young subjects would likely be amplified in a typical patient population. Does a halo-induced decreasein functional reach or unipedal stance have any relevance to clinical practice? These outcomes were used because of their association with balance and fall risk among older persons. Functional reach has been found to be a reliable, reproducible measure that correlates well with high technology parameters of postural stability I2 and has been found to be prospectively associated with fallsi Furthermore, fall risk has been found to increase progressively as functional reach declines. This would suggest that the decrease in functional reach we noted among healthy young subjects when wearing a halo vest would translate into an increased fall risk among older persons or frail patients. At the least the results would suggest that patients in a halo vest have a decreased reach that would likely affect their performance of activities of daily living. Unipedal stance time has also been found to identify older persons at increased risk for a fall. Cho and Kameni4 found that idiopathic failers demonstrated a decreased unipedal stance time compared with healthy age-matched older persons, and Vellas and colleaguesi5si6 noted that unipedal stance was a predictor of injurious falls among older subjects of both genders and for any fall among older men. We have also found that a decreased unipedal stance time is associatedwith a history of falls among ambulatory outpatients” and among subjects with peripheral neuropathy.i8 Because the outcomes used in this study have been tightly linked to fall risk and falls in older persons, who usually have a decreasedfunctional reserve, it is likely that the outcomes would apply to patients requiring a halo vest who also tend to have a decreased functional reserve. The findings therefore suggest that patients wearing a halo vest are likely at increased risk for lossesof balance and falls.

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Although the mechanism by which the halo vest causes the apparent adverse influence on balance was not investigated, some mechanisms can be postulated. As previously mentioned, cervical muscle proprioception has been found to influence eye movement and balance. Stabilizing the neck would prevent cervical muscle motion and likely lessen the efficiency of the involved proprioceptors. while stabilizing the head may prevent optimal positioning of the vestibular apparatus. The halo vest, which weighs approximately 8 pounds, would elevate the center of mass, which would make challenging balance maneuvers more difficult. In addition, although the weight of the halo vest might seem minimal, its mass is acting over a long lever during unipedal stance and functional reach and would therefore increase ankle muscle fatigue. Ottaviani and colleaguesI have found that near maximal ankle strength is required when the center of mass migrates near the edge of the foot during unipedal stance. Head motion may also be useful in terms of using the head’s mass for counter-balancing strategies when balance is being lost. This is likely particularly true for the functional reach, during which subjects without the halo vest were noted to extend their head and neck so as to keep their center of mass as posterior as possible while reaching forward. It is likely that a combination of these mechanisms is responsible for the balance impairment we have noted with the halo vest. Our results suggest that a halo vest causes a minor, acute impairment in balance in healthy young persons. Given the likely mechanisms of this impairment and findings from previous research, it is likely that the impairment would be greater in older or injured patients who are required to wear a halo vest for a period of months. Patients and families should be taught that even after recovery from any acute injuries the patient in the halo vest will have impaired balance, particularly when performing more challenging tasks of mobility and activities of daily living, such as climbing stairs and reaching for objects. The environment should be modified and assistance provided to minimize the chance of a fall, which might have devastating consequences in this vulnerable population. Acknowledgments: The authors would like to thank Mr. Eric Smith and Mr. Hank Brown of the Acromed Corporation, distributor of Bremmer products, for their support and assistance. References

I. Johnson RM, Hart DL, Simmons EF, Ramsby GL, Southwick WD. Cervical orthoses. A study comparing their effectiveness in restricting cervical motion in normal subjects. J Bone Joint Surg Am 1977;59:332-9. 2. Burl MM, Williams JG, Nayak USL. Effects of cervical collars on standing balance. Arch Phys Med Rehabil 1992;73:1181-5.

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3. Karlberg M, Magnusson M, Johansson R. Effects of restrained cervical mobility on voluntary eye movements and postural control. Acta Otolaryngol (Stockh) 1991;111:664-70. 4. Behrrnan S. Traumatic neuropathy of second cervical spinal nerves. BMJ (Clin Res Ed) 1983;286: 1312-3. 5. Persson L, Karlberg M, Magnusson M. Effects of different treatments on postural performance in patients with cervical root compression. A randomized prospective study assessing the importance of the neck in postural control. J Vestib Res 1996;6:439-53. 6. Kamath HO. Subjective body orientation in neglect and the interactive contribution of neck muscle proprioception and vestibular stimulation. Brain 1994;117: 1001-12. 7. Bronstein AM, Hood JD. The cervico-ocular reflex in normal subjects and patients with absent vestibular function. Brain Res 1986;373:399-408. 8. Igarashi M, Miyata H, Alford BR, Wright WK. Nystagmus after experimental cervical lesions. Laryngoscope 1972;82: 1609-2 I. 9. Igarashi M, Alford BR, Watanabe T, Maxian PM. Role of neck proprioceptors for the maintenance of dynamic bodily equilibrium in the squirrel monkey. Laryngoscope 1969;79:1713-27. IO. de Jong PTVM, de Jong JMBV, Coohen B, Jongkees LBW. Ataxia and nystagmus induced by injection of local anesthetics in the neck. Ann Neurol 1977; I :240-6. Il. Brandt T. Cervical vertig-reality or fiction? Audio1 Neurootol 1996;1:18-96. 12. Duncan PW, Weiner DK, Chandler J, Studenski S. Functional reach: a new clinical measure of balance. J Gerontol 1990;45: Ml92-7. 13. Duncan PW. Studenski S, Chandler J, Prescott B. Functional reach: predictive validity in a sample of elderly male veterans. J Gerontol 1992;47:M93-8. 14. Cho CY, Kamen G. Detecting balance deficits in frequent failers using clinical and quantitative evaluation tools. J Am Geriatr Sot 1998;46:426-30. 1.5. 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. 16. Vellas BJ, Wayne SJ, Philip GJ, Baumgartner RN. A two-year longitudinal studv of falls in 482 communitv-dwelling elderly adults. J Gerontol*1998;53A:M264-74. 17. Hurvitz EA. Richardson JK. Werner RA. Ruhl A. Dixon M. Unipedal stance testing and falls [abstrait]. Arch’ Phys Med Rehabil 1997;78: 1028. 18. Richardson JK, Hurvitz EA. Peripheral neuropathy: a true risk factor for falls. J Gerontol 1995;50A:M21 l-5. 19. Ottaviani RA, Ashton-Miller JA, Kothari SU, Wojtys EM. Basketball shoe height and the maximal muscular resistance to applied ankle inversion and eversion moments. Am J Sports Med 1995;23: 418-23. Suppliers

a. 3M Health Care, St. Paul, MN 55144-1000. b. Bremmer Medical, 4801 Dawn Rd., Jacksonville, FL 32207-95 12.

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