A clinical tool for measuring functional axial rotation.

Neck and back motion is used during many daily activities. The trunk and neck rotate relative to the pelvis when people look over their shoulders while driving or when they roll from a supine to a side-lying position. Because the axial structures (neck and torso) form the supportive base from which movement of the limbs and head occurs, die ability to move the neck and torso also influences movement of the extremities. Everyday functional activities require spinal motion that combines movements of multiple regions of the spine and in varying planes of motion.

Many devices have been developed that measure excursion or configuration of specific regions of the spine and in specific planes of motion.[1-7] For example, devices are available to measure lumbar motion,[1-4] cervical motion,[5] the degree of kyphosis,[6] and a forward head position.[7] In this technical report, we describe a device that we have developed to quantify the type of motion of the spine that is used during functional activities. During functional tasks, spinal motion generally involves many spinal segments and crosses multiple body planes (ie, triplanar motion). For convenience, we use die term "combined spinal motion" to describe die axial movements that occur during the performance of functional activities. We believe that information obtained by measuring combined spinal motion complements information that is obtained from devices that measure specific regional mobility. We use the term "functional axial rotation" (FAR) to refer to movements of the neck and torso that position the head toward the posterior as would occur when one looks behind oneself (eg, when backing a car). Functional axial rotation is a specific example of combined spinal motion. The combined motion includes movement of vertebral segments from the cervical to the lumbar spine. What we can FAR occurs predominantly in the transverse plane but may be accompanied by extension, lateral flexion, and sometimes even flexion of specific spinal regions.

This pattern of FAR has two distinct purposes. The first purpose is to allow the head and thorax to move with respect to the pelvis so that functional activities can occur. This movement is exemplified by rotation of the head and thorax relative to the pelvis, as when one rolls from a side-lying to a supine position. Axial motion can be quantified by the physical distance that the head can be moved with respect to the pelvis. The second purpose is to allow individuals to see objects positioned toward their posteriors. The ability of a person to use vision in combination with available axial mobility can be quantified by having the person identify objects located toward the posterior.

The FAR device we have developed is designed to reflect physical action (movement) and visual performance. First, the device is used to measure the physical distance that people can turn when they are not constrained to a particular strategy. This device is only intended to reflect the subject's capability for movement without determining the causes of limitations (eg, joint or soft tissue restrictions, pain). Second, the device is used to measure the range through which people can identify symbols when they turn. This ability is determined in part by FAR, but may be further limited by visual deficits (eg, loss of acuity, visual-field limitations, perceptual deficits, or other impairments of the visual system).[8] The FAR measures are designed to determine how successful a person can be in physically moving the spine and in identifying objects to the posterior without consideration for the specific impairments that might limit performance.

We had several criteria for the device. First, we wanted to be able to measure rotation of the neck and trunk relative to the fixed pelvis in order to reflect axial motion. We therefore chose to use the seated position to assist in stabilizing the pelvis. second, we wanted the device to be inexpensive, practical for use in most clinics, and portable for use in a variety of community settings. Third, we wanted it to have a minimum resolution of 5 degrees in order to be useful for detecting clinically meaningful changes over time and between subjects. Finally, we wanted to differentiate between the range of motion (ROM) of subjects and their capability to use that motion visually.

Method

Equipment

The FAR measurement tool that we developed consists of a 1-m-diameter circular hoop that is suspended, by tripods, at eye level around the seated subject (Figure). We used a commercially available child's toy hoop(*) for this purpose in our prototype. We subsequently developed a more permanent device, using a 2.54-cm-wide, flat metal band, secured by rivets to create a hoop that is 1 m in diameter. The hoop is divided into four equal quadrants by marking it with vertical lines that can be aligned with the subject's body. We placed symbols, consisting of numbers and letters, in 5-degree increments around the inner ring of the hoop (Figure). The symbols are randomly ordered to provide a value-neutral target for the subject. We constructed a key relating each symbol to the amount of rotation it represents in order to convert symbols to ROM values. A pointer is affixed to the subject's forehead, using the headpiece provided by the cervical range of motion device (CROM[TM]).[dagger5] Although we choose to use the headpiece of the CROM[TM] for convenience, we believe any method for fixing a horizontal pointer to the head could be used.

With the FAR device, combined axial motion is quantified in two ways:

1. The displacement of the subject's

head relative to the fixed pelvis is

determined by the location of the

symbol with which the headpiece

is aligned once motion is completed

(Figure). We call this measure

"functional axial rotation physical"

(FAR-p).

2. The subject's success in visualizing

objects in the transverse plane is

determined by the symbol that the

subject can read when rotating as

far as possible in one direction. We

call this measure "functional axial

rotation-visual" (FAR-v).

Subjects

Subjects were recruited from the Duke Medical Center Aging Center registry, the Department of Veteran's Affairs Medical Center in Durham (NC), and the Duke University Graduate Program in Physical Therapy. Subjects were excluded if they had pathology of the axial skeleton (eg, fusion of the spine or compression fractures), if they had reportedly been on bed rest during the past year because of back pain, or if they were currently experiencing back pain. They were also excluded they reported focal neurologic conditions that might potentially contribute to functional impairment (eg, Parkinson's disease, stroke). Nine men and eight women, ranging in age from 20 to 74 years, participated (Tab. 1). All subjects gave informed consent prior to participation in the study.

Table 1. Subject Characteristics (N=17)
               Minimum     Maximum     X[bar]        SD
Age(y)          20          74          48.8         21.6
Height(cm)(a)  152.4(60)   185.4(73)   167.9(66.1)    8.9(3.5)
Weight(kg)(b)   50.8(112)   97.5(215)   69.2(152.5)  16.2(35.6)
(a) Nonmetric equivalent (in inches) shown in parentheses.
(b) Nonmetric equivalent (in pounds) shown in parentheses.

Procedure

To position each subject, the hoop, suspended from two adjustable tripods, was placed around the seated subject (Figure). The height of the hoop was adjusted to eye level. To ensure that the hoop had the same orientation from trial to trial, the front of the hoop (0 [degree]), marked by a vertical line, was aligned with the midline of the subject's face, and the back of the hoop (180 [degrees]) was aligned with the seventh cervical vertebra. The hoop was then moved in the anterior/posterior direction until the two lines, at 90 and 270 degrees, respectively, were positioned in line with the subject's greater trochanters. To ensure that rotational motion was accomplished without lifting the pelvis, the subject's pelvis was secured to the chair seat using two straps, crossed to form a figure eight. The headpiece was then fitted over the subject's head with the pointer oriented toward the hoop.

To measure FAR, subjects were instructed to let their hands hang loosely by their sides and to turn as far to the left or right as possible and read the farthest symbol that they could see. Subjects were also instructed to move the neck and torso as much as they could but to refrain from gripping the chair seat with their hands. Subjects were not restricted with respect to the motion of the torso (eg, axial extension, lateral flexion, flexion). The tester observed the motion carefully to ensure that the subjects' buttocks were not lifted from the chair seat.

Data were obtained for rotation (FAR-p) and for reports of symbols (FAR-v) to both the left and to the right. Three trials were collected for each side, alternating from right to left side between trials. The first trial in each direction was a practice trial; the second and third trials to each side were test trials.

Measurements of FAR-p and FAR-v were taken on 2 different days (5-10 days apart) to determine test-retest reliability. On the second day of testing, FAR-p was measured by two different raters (FAR-v was not measured by two raters because this is a measure of the symbol reported by die subject).

Data Analysis

Data from die two test trials for FAR-p were averaged to determine FAR-p right and FAR-p left, respectively. Averaged values were used for further analysis. Similarly, the average values for FAR-v right and FAR-v left were determined and used m further analyses. We used the ICC[9] to determine interrater reliability (ICC[2,1]) and test-retest reliability (ICC[1,1]).

Results

For the 17 subjects and the 2 days of measurement, FAR-p ranged from 92 to 190 degrees and FAR-v ranged from 135 to 250 degrees (Tab. 2). The mean difference between days was 8 degrees for FAR-p and 9 degrees for FAR-v. Differences between raters in measuring FAR-p are shown in Table 3. The mean difference between the two raters in the determination of FAR-p was 1 degree.

Table 2. Functional Axial Rotation-Physical (FAR-p) and Functional
Axial
Rotation-Visual (Far-v) (in Degrees) in 2 Different Days (N=17)
                 Test  Minimum       Maximum
Variable  Side   Day   Displacement  Displacement  X[bar]  SD
FAR-p     Right  1     100           185           140     20
FAR-p     Right  2     105           188           141     20
FAR-p     Left   1      92           182           133     22
FAR-p     Left   2     102           190           134     21
FAR-v     Right  1     142           240           187     23
FAR-v     Right  2     150           238           185     21
FAR-v     Left   1     135           238           179     24
FAR-v     Left   2     152           250           181     24
Table 3. Functional Axial Rotation-Physical (FAR-p) (in Degrees)
Measured by
Two Different Raters (n=15)
                        Minimum       Maximum
Variable  Side   Rater  Displacement  Displacement  X[bar]   SD
FAR-p     Right  1      80            170           138      20
FAR-p     Right  2      80            170           138      22
FAR-p      Left  1      78            162           135      22
FAR-p      Left  2      80            162           134      22

Test-retest reliability was excellent for both FAR-p and FAR-v (ICC[1,1] values of .95 and .90, respectively, were obtained for rotation to the right and to the left). Interrater reliability likewise was excellent (ICC[2,1] values of .97 were obtained for rotation to the right and to the left).

Discussion

This technical report illustrates a method for estimating die extent to which a person can use combined spinal motion for function. We believe the method may provide a more functional approach to determining capability than do die specific measures of regional mobility or vision. The fact that people have a particular amount of axial mobility at specific joints--or a particular acuity, visual field, perceptual ability, and so forth--does not ensure that they will use those abilities in functional contexts. Specific regional restrictions also do not necessarily imply that people will fail in a functional context. People may adopt a movement strategy, such as leaning back while rotating, to extend the functional ROM through which they can move the torso.

The FAR-p and FAR-v measures potentially quantify two different aspects of function that depend on combined spinal movements. The FAR-p measure quantifies the available ROM through which the seated subject can turn the torso relative to the pelvis.

This measure could be limited by impairments such as joint restrictions or malalignment, soft tissue tightness, or pain. If FAR-p is limited, further testing would be required to determine the underlying causes. The FAR-v measure quantifies the person's ability to describe objects located to the posterior. In concept, this measure is related to whether a person will "see the child on the bicycle that he or she is about to back into." This measure is analogous to the FAR-p measure in that it could quantify how successfully a person can complete a functional task--not the reasons for difficulty or failure. The FAR-v measure depends on both ROM and vision. This measure, therefore, is interpreted with respect to both factors. If people demonstrate limited FAR-v relative to FAR-p, further testing would be necessary to determine whether they have deficits of acuity, visual fields, perceptual ability, or a host of other visual and/or cognitive possibilities. The FAR-v and FAR-p measures are closely related but would not necessarily have a one-to-one correlation, because the ability to describe objects located to the posterior requires more than the ability to rotate the axial skeleton. Research is needed to validate functional inferences regarding both measures.

We developed the FAR measures in order to investigate the functional importance of axial mobility.[10] It is clear from a clinical perspective that the axial structures play an important role in many functional activities. Yet, there are few physical performance measures available that capture information related to motion of the axial segments. We were particularly concerned with the functional use of rotational motion because of its importance for many daily activities, including bed mobility, dressing, and driving a car.

A first step toward using this measurement approach, either for clinical practice or for research, was to establish that the FAR measure provides reliable information. Intertester reliability is important because the device should be useful for more than one rater. Test-retest reliability is particularly important because FAR-p is not constrained to a single plane or a single region of the spine. There is no attempt to restrict how the motion is accomplished; thus, there is considerable potential for variability in the way that the task might be carried out on different occasions. Variability in performance of the task could lead to variability of the available ROM measured by the FAR device. our results indicate that this functionally relevant approach to measurement of axial motion can provide highly reliable results, both when used by different raters and when the same subjects are measured on different days. Because of our interest in determining how FAR mobility changes with age, we chose to investigate healthy individuals in this work. Additional studies are needed to determine reliability for other populations.

One potential concern in using the FAR device was that the subjects might use the symbols as a guide when repositioning their torso on repeated tests. The excellent test-retest reliability across a week argues against this. Furthermore, we have used this measure to quantify axial mobility of patients with Parkinson's disease.[10] Using an analysis of variance to compare the data obtained on 4 different days of testing, we established that there is no systematic difference by day or week of testing. In light of the data in this report, as well as the data we obtained with patients who have Parkinson's disease, it is highly unlikely that the reliability that we obtained simply reflects the subjects' ability to recall the symbols.

Improvement of a patient's mobility of the neck or back through mobilization, other manual therapy techniques, or exercise should lead to improvement of the coordinated use of spinal movements for activities such as looking over one's shoulder. Clinicians should be able to quantify improvements in this ability. The FAR measurement device is easy to construct, easy to use, and portable. The device can be used in clinical as well as research settings and can provide the clinician with a new and important measure of functional capability. Further work is under way in our laboratories to establish the reliability of this measurement approach for individuals with a specific pathology,[11] to determine how FAR relates to other aspects of physical performance,[9] and to determine whether improvements of FAR lead to improvements of ability for a variety of activities.

Conclusion

The FAR device that we have developed was designed as one means of quantifying a patient's combined axial motion as it would be used in functional contexts. The device is easy to construct, portable, and easy to use in the clinic or in the patient's home. The device provides the clinician with information regarding the patient's ability to move the spine in an integrated fashion and permits the clinician to characterize the patient's ability to see objects toward the posterior. Further research is needed to establish the reliability and validity of measurements obtained with the FAR device on other clinically relevant populations. (*) Hula Hoop[TM], Wham-O Manufacturing Co, 835 E El Monte, San Gabriel, CA 91778. [dagger]Performance Attainment Associates, 958 Lydia Dr, Roseville, MN 55113.

References

[1] Fitzgerald GK, Wynveen KJ, Rheault W, Rothschild B. Objective assessment with establishment of normal values for lumbar spinal range of motion. Phys Ther. 1983;63:1776-1781. [2] Mayer TG, Tencer AF, Kristoferson S, Mooney V. Use of noninvasive techniques for quantification of spinal range-of-motion in normal subjects and chronic low-back dysfunction patients. Spine. 1984;9:588-595. [3] Dillard J, Trafimow J, Andersson GBJ, Cronin K. Motion of the lumbar spine: reliability of two measurement techniques. Spine. 1991; 16:321-324. [4] Salisbury PJ, Porter RW. Measurement of lumbar sagittal mobility: a comparison of methods. Spine. 1987;12:190-193. [5] Rheault W, Albright B, Byers C, et al. Intertester reliability of the cervical range of motion device. J Orthop Sports Phys Ther. 1992; 15:147-150. [6] Ohlen G, Spangefort E, Tingvall C. Measurement of spinal sagittal configuration and mobility with Debrunner's Kyphometer. Spine. 1989;14:580-583. [7] Hanten WP, Lucio RM, Russell JL, Brunt D. Assessment of total head excursion and resting head posture. Arch Phys Med Rehabil. [8] Green HA, Madden DJ. Adult onset differences in visual acuity stereopsis and contrast sensitivity. Am J Optom Physiol Optics. 1987; 64:749-753. [9] Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. Psychol Bull. 1979;86:420-428. [10] Schenkman M, Cutson T, Chandler J, et al. Reliability of measures for Parkinson's disease. In: Proceedings of the Annual Meeting of the American Geriatrics Society; Los Angeles, Calif; May 21, 1994, 1994:SA-77. [11] Prescott BL, Schenkman M, Bowden MG, et al. Spinal mobility: age effects and relationship to functional performance. In: Proceedings of the Gerontological Society of America. 1992:127-128.

M Schenkman, PhD, PT, is Associate Professor, Graduate Program in Physical Therapy, Senior Fellow, Center for the Study of Aging and Human Development, and Co-Director, Claude Pepper Older American Independence Center, Duke University, Durham, NC 27710. Address all correspondence to Dr Schenkman at the Center for the Study of Aging and Human Development, Duke University Medical Center, PO Box 3003, Durham NC 27710 (USA).

MA Hughes, is Biomedical Engineer, Postural and Balance Control Laboratory, Department of Veterans Affairs, Durham, NC 27701.

MG Bowden, is Research Assistant, Postural and Balance Control Laboratory, Duke University.

SA Studenski, MD, is Director, Center for the Study of Aging and Human Development, University of Kansas, Lawrence, KS 66045. She was Director, Rehabilitative Medical Services, Department of Veterans Affairs, Durham, NC, when this work was initiated.