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PHYS THER
Vol. 81, No. 3, March 2001, pp. 903-912
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Research Reports

Relationships Among Selected Measures of Impairment, Functional Limitation, and Disability in Patients With Cervical Spine Disorders

Karl M Hermann and C Shane Reese

KM Hermann, PT, PhD, is Director, The Therapy Center, College Station Medical Center, 1605 Rock Praire Rd, Ste 5, College Station, TX 77845 (USA) (hermannkarl{at}hotmail.com).
CS Reese, PhD, is Technical Staff Member, Statistical Sciences, Los Alamos National Laboratory, Los Alamos, NM. Dr Reese was a doctoral candidate in the Department of Statistics, Texas A&M University, College Station, Tex, at the time of the study

Address all correspondence to Dr Hermann


Submitted February 10, 2000; Accepted August 31, 2000


   Abstract
 
Background and Purpose. Little is known about the relationship among impairments, functional limitations, and disability in people with cervical spine disorders (CSD) despite the fact that these concepts are routinely used in clinical practice. The primary purpose of this study was to investigate the relationships among commonly assessed impairment, functional limitation, and disability measures in patients with CSD. A secondary purpose was to determine the influence of payment source and time since onset of symptoms on these same measures. Subjects. Eighty patients (mean age=45.7 years, SD=15.9, range= 20–88) with CSD who were referred for physical therapy participated in the study. Methods. Data were obtained for 3 measures of impairment, 2 measures of functional limitation, and 3 measures of self-reported disability during the initial visit. Results. All 3 sets of variables (ie, impairment, functional limitation, disability) correlated with each other, with the highest correlation occurring between the impairment measures and the functional limitation measures (r=.82). Other correlations were noted between individual variables. There was no effect of payment type or time since onset of symptoms on the variables. Conclusion and Discussion. Positive correlations were noted among the 3 sets of measures, which supports the assumption that impairments, functional limitations, and disability are related in patients with CSD.

Key Words: Cervical spine • Neck pain • Physical examination


   Introduction
Top
 Abstract
 Introduction
Method
 Results
 Discussion
 Conclusion
 References
 
Cervical spine disorders (CSD) are a common cause of neck pain. Population-based surveys have shown lifetime prevalence rates for neck pain between 67% and 71%,1,2 whereas between 13% and 22% of the population in industrialized society experiences neck pain at any point in time.1,3 Cervical spine disorders are not just limited to adults. A recent survey of Finnish high school students showed that 21% of women and 10% of men experienced neck or shoulder pain at least once per week.4 Cervical spine disorders also account for a substantial number of physical therapy outpatient visits each year. In one report, CSD accounted for 26% of outpatients seeking physical therapy treatment.5

When patients with CSD first see a physical therapist, an examination process should occur so that a plan of care can be established and treatment goals can be set.6 Although there are no research data, some authorities advise assessment of posture, joint range of motion (ROM), and strength among other variables with the assumption that these relate to functional loss.6,7 Changes in these variables are then supposed to be used to monitor progress and guide treatment. In addition, measures of cervical ROM have been used to evaluate the severity of impairment8 or disability9 in patients with work-related CSD.

Many people propose using a disablement model in physical therapy research and practice.6,10 A disablement model links a disease or pathology to functional consequences. One such model is the International Classification of Impairments, Disabilities, and Handicaps (ICIDH).11 In this model, there are 4 sequential concepts: disease, impairment, disability, and handicap. This model has been criticized for its definitions of the disability and handicap concepts in that there is some overlap leading to confusion in how to classify an individual with multidimensional limitations.10 More recently, a modified version, the ICIDH-2,12 was developed. The ICIDH-2 model classifies information at 3 levels of functioning (ie, body, activity, and society). These levels are known as "dimensions" and are named "Body Functions and Structure," "Activities," and "Participation," respectively. Each dimension consists of "domains" or categories that are used to further classify information. Contextual factors (ie, environmental and personal) that may influence an individual's state are also included.

In this study, we used a well-known disablement model initially proposed by Nagi.13 This model also contains 4 sequential concepts: pathology, impairments, functional limitations, and disability. In theory, pathology produces impairments, which then lead to functional limitations, which then result in disability. Not all impairments result in functional limitations, however, and not all functional limitations result in disability. In order for the clinician to provide effective care that will ultimately affect function and reduce the potential for disability, therapeutic interventions should, in theory, target only those impairments that are related to (or producing) the functional limitations. Indeed, it has been suggested that, through the examination process, the clinician determines the interrelationships among impairments, functional limitations, and disability for a patient with a given diagnosis and that this information then guides treatment.6 Examples of cervical spine impairments include deficits in ROM or muscle force, whereas a functional limitation might be a driver's inability to rotate the head and neck to be able to see behind when driving an automobile in reverse. If an individual is then unable to work because his or her occupation requires automobile use, that person could be considered to have a disability.

Little is known about the relationship among impairments, functional limitations, and disability concerning the cervical spine. Schenkman and coworkers14 have shown a relationship between cervical ROM and "functional axial rotation" (FAR). The FAR test is a measure of combined spinal motion that, in turn, correlates with measures of physical performance, but does not reflect function as it is often defined. In an earlier study, this same group demonstrated that measures of FAR can be used to infer the amount of rotation available for the performance of functional activities.15 However, the subjects in both of these studies were volunteers without cervical spine pathology. Hagen et al16 examined the relationship between self-reports of neck pain and limited or painful cervical ROM in 49 male machine operators. They found a weak inverse relationship between cervical ROM and pain experienced within that ROM for extension (r=–.29, P=.04) and left axial rotation (r=–.32, P=.03). Stronger relationships were observed between cervical ROM and the corresponding pain level and self-reports of pain on the Standardized Nordic Questionnaire. More recently, Riddle and Stratford17 reported weak correlations (r=.12–.40) between cervical ROM and functional status measurements obtained from the Neck Disability Index (NDI) and the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). Another investigation demonstrated a positive correlation (r=.65, P<.001) between pain scores on a visual analog scale (VAS) and self-reported disability using the NDI in subjects with neck pain.18

Relationships involving cervical muscle force and endurance have also been investigated. A recent report showed low correlations (r ≤ .20) between cervical extensor force, endurance, and ROM on the one hand, and pain and disability on the other.19 Another study documented improved cervical extensor force and endurance in patients with neck pain and also reported a 50% reduction in pain and disability.20 Subjects in this study did not show improvements in cervical flexor force or extension ROM. A relationship between postural abnormalities and the incidence of pain in the cervical region has also been demonstrated.21

We believe that these findings indicate a disparity in level of association among measures of impairment, functional limitation, and disability in subjects with CSD and suggest the need for further study. According to the disablement model developed by Nagi,13 impairment is defined as any loss or abnormality of anatomic, physiologic, mental, or emotional structure or function. Functional limitation is defined as a limitation in performance at the level of the whole organism or person.13 Disability then applies to a limitation in performance of socially defined roles and tasks within a sociocultural and physical environment.13 If the relationships among physical impairments, functional limitations, and disability in patients with CSD were known, we believe clinicians could examine patients in a more efficient manner, provide a more accurate prognosis, and gauge progress through a therapeutic regimen based on more valid measures. This information could also be useful for providing rationales for treatment to third-party payers.6 Therefore, the primary purpose of this study was to investigate the relationship among specific cervical spine impairments, functional limitations, and disability in patients with CSD. More specifically, we sought to determine the associations among 3 measures of impairment (pain, ROM, and muscle force), 2 measures of functional limitation (FAR and a test of lifting ability), and 3 self-report measures of disability (NDI and 2 summary scales from the SF-36) in this patient population. A secondary purpose was to determine the influence of payment source and time since onset of symptoms on these same measures.


   Method
Top
 Abstract
 Introduction
 Method
Results
 Discussion
 Conclusion
 References
 
Subjects

We recruited consecutive patients who were referred to a hospital-based outpatient physical therapy clinic and who met the inclusion criteria. All patients were referred by a physician (doctor of medicine or doctor of osteopathy). The inclusion criteria were (1) a primary diagnosis of neck pain or cervical pathology by the referring physician, (2) no contraindications to ROM or muscle force testing or to the performance of a functional lift test, and (3) the ability to read and write English. Subjects were excluded if they had comorbidities that would affect test performance (eg, low back pain, shoulder pathology). A total of 80 subjects (32 men, 48 women) fulfilled these criteria and were included in the study. The subjects' ages ranged from 20 to 88 years (X=45.7, SD=15.9). Subject demographic data are presented in Table 1.


View this table:
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[in a new window] 		Table 1. Demographic Characteristics of the Subjects (N=80)

 
Testing Procedure

After obtaining written informed consent, scores for 3 measures of impairment, 2 measures of functional limitations, and 3 measures of disability were obtained from each subject during the initial visit (ie, before any treatment intervention occurred). The entire testing procedure took approximately 45 minutes. Each subject was tested by 1 of 3 physical therapists who had 11, 3, and 2 years of experience, respectively.

Impairment Measures

The impairment measures were pain, cervical spine ROM, and cervical muscle force. These 3 variables were chosen because they are commonly assessed in clinical practice and because they have been used in previous studies.16,18–20,22–25 Pain was assessed through the use of a VAS consisting of a 10-cm vertical line with the anchors "Pain as bad as it could be" and "No pain at all."26 Subjects were instructed to draw a mark across the line that corresponded to their pain level at that moment. Acceptable reliability of the VAS scores has been shown previously (r=.98, N=39).27

Cervical spine ROM was assessed using the Cervical Range of Motion (CROM) device* in a manner similar to Youdas et al.25,28 Subjects were positioned sitting in a metal framed chair with their thoracic spine in contact with the chair's backrest, their feet flat on the floor, and their arms hanging at the sides. To overcome initial apprehension and to increase tissue compliance, subjects performed one movement each of cervical flexion, cervical extension, left lateral flexion, right lateral flexion, left rotation, and right rotation. They then performed 2 subsequent series of movements in the same order. Subjects were instructed to move their head and neck as far as possible until the active ROM was stopped by pain or muscle tightness or until a substitution movement occurred. The mean value for each position during these 2 movement series was then calculated and used for further analysis.

Although acceptable reliability for measuring cervical spine ROM using the CROM device has been shown previously (intraclass correlation coefficient [ICC] (1,1)>.80, N=60),25 intertester reliability for this same test as well as for muscle force and the 2 functional limitation measures was determined for the purposes of this study. Eight subjects (2 men and 6 women) ranging in age from 17 to 52 years (X=33.4, SD=11.1) with no history of cervical pathology were tested on one occasion by each tester. A minimum of 4 hours separated the tests. The testers were unaware of each other's results. Intraclass correlation coefficients (ICC [2,1])29 were calculated for each measure. For the cervical ROM measurements, intertester reliability ranged from .70 for cervical rotation to .88 for cervical flexion.

In our study, the isometric force of the cervical flexor and extensor muscles was measured with a handheld dynamometer{dagger}. The dynamometer was calibrated prior to the initiation of the study, at the end of the study, and at 6-month intervals according to the manufacturer's instructions. Cervical flexor force was measured in a manner that has been performed previously.19,23 Subjects were positioned supine with their chin retracted and neck flexed approximately 20 degrees. The dynamometer was placed over the forehead, and resistance was applied by the tester until this position could no longer be maintained (ie, break test). Cervical extensor force was measured with the subjects in a prone position and the cervical spine in approximately 20 degrees of extension. The dynamometer was placed just superior to the occiput, and resistance was applied until the test position could no longer be maintained. For each position, three 5-second contractions with 30- to 60-second rest periods were performed. The recorded force was the force the tester had to apply to break the isometric contraction and move the subject's head in the opposite direction. The mean value of the 3 measurements was then calculated for both test positions and then normalized to body weight. Similar to the findings of others,19,23 intertester reliability (ICC [2,1]29) in this study was .93 and .70 for cervical flexor force and cervical extensor force, respectively. We believe we have provided some evidence for the reliability of our measures, but we recognize that one limitation to our study was that reliability was not determined for subjects with CSD.

Functional Limitation Measures

Two measures of functional limitation were recorded: a measure of combined spinal motion (the FAR test) and a lift test. Combined spinal motion is a component of many routine daily activities (eg, reaching, looking behind oneself). Intuitively then, the FAR test could be a measure of function, although data in support of this are lacking. The FAR test was performed according to the procedure described by Schenkman et al.15 Subjects sat inside a hoop, which was suspended by 2 tripods at eye level, with their feet flat on the floor and their arms hanging at their sides. Subjects were instructed to rotate the head, neck, and trunk to either side as far as possible without lifting their buttocks from the chair seat. The pelvis was stabilized with a Velcro strap.{ddagger} The amount of motion was measured by aligning a pointer attached to the subject's head with landmarks on the hoop corresponding to degrees of rotation. Three trials to each side were performed, with the first trial serving as a warm-up. The mean value of the following 2 trials were computed and used for subsequent analysis. Intertester reliability (ICC [2,1]29) for right and left FAR was .76 and .80, respectively. There is no research to support whether this measure of impairment actually predicts function.

A test of lifting capacity, another impairment measure thought to relate to function, was used in this study.30,31 The test involved a cycle of lifting a weighted box (3.6 kg for women, 5.9 kg for men) from a 76.2-cm-high shelf to a 137.2-cm-high shelf and back again. Subjects were required to complete 4 cycles within 20 seconds. If all 4 cycles were successfully completed in the 20-second time period, the weight was increased by 2.2 kg for women and 4.5 kg for men. The test continued until 1 of 3 endpoints was reached: (1) 85% of age-adjusted maximal heart rate (220 – age) was achieved, (2) the limit of fatigue or pain was reached as determined by the subject, or (3) subject safety was at risk as evidenced by a substitution pattern. The final weight was recorded and normalized to adjusted body weight as specified by Mayer et al.30 In this study, intertester reliability (ICC [2,1]29) for the lift test was found to be .88.

Disability Measures

Both a condition-specific and a generic instrument for self-report of disability and health-related quality of life were used in our study. The NDI32 is an adaptation of the Oswestry Low Back Pain Questionnaire.33 It consists of 10 items (subscales) containing 6 statements each that evaluate pain, sleep quality, work ability, and various activities of daily living. The questionnaire was scored as a percentage. High scores indicate a high level of perceived disability, and low scores indicate a low level of perceived disability. Vernon and Mior32 found test-retest reliability (Pearson product moment correlation coefficient) for the NDI to be .89.

The generic instrument used was the SF-36,34 which is a self-administered 36-item questionnaire designed to assess general health status. The SF-36 is composed of 8 subscales, each of which measures a distinct component of health status: (1) physical functioning, (2) social functioning, (3) bodily pain, (4) role limitations due to physical problems, (5) role limitations due to emotional problems, (6) general mental health, (7) vitality (energy or fatigue), and (8) general health perceptions. Each component is scored on a scale from 0 to 100, with higher scores representing better health status for that component. In addition, 2 summary scales can be obtained: the physical component summary scale (PCS) and the mental component summary scale (MCS). These scales represent the physical and mental components of health, which are based on weighted aggregates of all 8 subscales, and they were used in this study. Acceptable reliability for the SF-36 has been reported previously.35 The SF-36 was scored using the statistical software the developers provided with the test.36

Order of Testing

The order of testing was the same for all patients, as follows: measurements of pain with the VAS, measurements of cervical ROM and FAR, measurements of force, performance of the lift test, and completion of the NDI and SF-36 questionnaires. Pain measurement was done first in an attempt to eliminate the effects of subsequent test procedures on this variable.

Data Analysis

Subjects were placed in 1 of 3 groups depending on the amount of time since the onset of symptoms (ie, acuity): acute (0–14 days), subacute (15 days–6 months), and chronic (>6 months). Descriptive statistics were used to characterize the 3 groups and their scores on the dependent measures. Before further analysis, a principal component analysis was performed on the cervical ROM, muscle force, and FAR measurements in order to reduce the number of variables entered into the correlation analysis. The main benefit of using a principal component analysis is the ability to represent the variability of several variables by a statistically determined linear combination of those variables. This reduces a multivariate problem into a univariate problem. In our study, we used principal component analysis to find the linear combination of each group of measurements (cervical ROM [6 measurements], muscle force [2 measurements], and FAR [2 measurements]) that accounted for the greatest amount of variation inherent in those measurements, making it the most representative variable to summarize that group of variables. The result is 3 variables (ROM, muscle force, and FAR) rather than the original 10.

Canonical correlations were then calculated to examine relationships among the 3 sets of variables (ie, impairment, functional limitation, disability measures) while controlling for age, sex, and acuity. Canonical correlation is a multivariate technique for assessing relationships between groups of variables. It determines which combination of variables results in the largest correlation. The resulting weights indicate how the variables within a group contribute to the relationship. To assess the relationship between individual variables, a correlation matrix was calculated while again controlling for age, sex, and acuity. Because scores on the VAS and the disability measures cannot be considered ratio levels of measurement, a Spearman rank correlation coefficient was used. In addition, because the analysis for the individual variables involved 28 correlations, we set the time since onset of symptoms at 2 levels: acute (0 days–6 months) and chronic (>6 months). This served to decrease the number of variables used in calculating the correlation matrix for the individual variables. A multivariate analysis of variance (MANOVA) was used to determine whether there were any differences due to time since onset of symptoms (acute, subacute, chronic) or source of payment (managed care or fee-for-service) for the impairment, functional limitation, and disability measures while controlling for age and sex. Because several correlations were calculated, the alpha levels for the canonical and individual correlations were adjusted to maintain an experiment-wise error rate of .05. The canonical correlations were performed at an alpha level of .015, and the individual Spearman correlations were performed at .0024.

The sample (N=80) in this study consisted of more women (n=48) than men (n=32), a finding consistent with cross-sectional studies reporting higher prevalence rates of CSD in women.1,3 All age groups were represented except for those under 20 years. Subject scores on the dependent measures are shown in Tables 2, 3, and 4. The data were variable within each group. Despite the 3 different acuity levels, however, little disparity between groups was noted. The results of the principal component analysis revealed that, for the 6 cervical ROM measurements, 66% of the variability within these measurements could be accounted for by one linear combination of the 6 ROM measurements. The linear combinations determined by principal components analysis for the FAR measurements and muscle force measurements accounted for 92% and 90% of the variability within these measurements, respectively.


View this table:
[in this window]
[in a new window] 		Table 2. Subject Scores on the Impairment Measuresa

 

View this table:
[in this window]
[in a new window] 		Table 3. Subject Scores on the Functional Limitation Measures

 

View this table:
[in this window]
[in a new window] 		Table 4. Subject Scores on the Disability Measuresa

 

   Results
Top
 Abstract
 Introduction
 Method
 Results
Discussion
 Conclusion
 References
 
The canonical correlations among the impairment, functional limitation, and disability measures are shown in Table 5. All 3 sets of variables were correlated with each other, with the highest correlation occurring between the impairment measures and the functional limitation measures (r=.82, P<.0001). The canonical correlation measures not only the correlation between groups of variables, but which variables contribute most to the relationship. For the relationship between impairment and functional limitation measures, the variable that contributed most to the relationship was ROM for the impairment measures (ROM [.69], force [.36], pain [–.17]), and FAR for the functional limitation measures (FAR [.77], lift test [.44]). The impairment measures also correlated with the disability measures (r=.73, P<.0001). In this relationship, the greatest contribution was pain for the impairment measures (pain [.73], ROM [–.47], force [.03]) and the NDI for the disability measures (NDI [1.02], MCS [.04], PCS [.01]). A weaker relationship was noted between the functional limitation measures and the disability measures (r=.54, P<.0001). Here, the greatest contribution was the lift test for the functional limitation measures (lift test [.68], FAR [.55]) and the NDI for the disability measures (NDI [–.85], PCS [.21], MCS [.00]). In this relationship, the coefficient for the NDI is negative because of its inverse relationship to the other measures (ie, higher scores for the NDI imply greater limitations, whereas high scores for the other measures imply fewer limitations). The absolute value of the coefficient denotes the relative weight contributed by a given variable to the relationship.


View this table:
[in this window]
[in a new window] 		Table 5. Canonical Correlations Between Variable Sets

 
The correlation matrix for the individual variables is presented in Table 6. Of the 28 possible individual correlations, 17 were significant. Six of the 11 correlations that were not significant involved the MCS. Particularly strong inverse relationships were noted between the PCS and the NDI (–.67) and between ROM and the NDI (–.54). Strong relationships were also noted between pain and the NDI (.65), ROM and FAR (.65), and ROM and the lift test (.56). The results of the MANOVA did not show any influence of time since onset of symptoms (P=.83) or payment type (P=.14) on the dependent measures (Tab. 7).


View this table:
[in this window]
[in a new window] 		Table 6. Spearman Rank Correlation Coefficients Between Individual Variablesa

 

View this table:
[in this window]
[in a new window] 		Table 7. Relationship Between Time Since Onset of Symptoms and Payment Type on the Measured Variables

 

   Discussion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
Conclusion
 References
 
The results of the canonical correlations lend support to what many clinicians intuitively believe to be correct: that, in patients with CSD, there are links between observed impairments and a person's ability to function and his or her perceived level of disability. The impairment measures correlated strongly with the functional limitation measures (r=.82, P<.0001). This relationship was driven primarily by the 2 variables addressing axial mobility: ROM and FAR. Cervical rotation is a component of FAR, and, therefore, it is not surprising that a positive correlation was found between the impairment measures and the functional limitation measures. A similar finding was reported by Schenkman et al14 in a population of subjects without spinal pathology. Cervical ROM is commonly assessed in patients with CSD.25,37

The impairment-disability relationship was driven primarily by pain and the NDI, 2 self-reported measures. The relationship between these 2 variables individually was also quite strong (r=.65, P<.0001). Pain intensity is 1 of the 10 areas addressed on the NDI. A relationship between these 2 variables, therefore, would be expected. The relatively minor contribution to the impairment-disability relationship by the PCS and MCS is consistent with a previous finding that showed small changes (compared with population norms) in many of the health domains of a modified version of the SF-36 in patients with neck sprain and both radiating and nonradiating neck pain.38 This finding also points out the importance of using a condition-specific instrument for assessment of self-perceived disability in patients with CSD.

The lift test and the NDI contributed most to the relationship between the functional limitation and disability measures. The lift test used in this study has been used previously to assess cervical functional ability.30,31 It involves lifting a weighted box to approximately head height and, as such, would be expected to require some degree of cervical muscle strength. This idea is supported by the individual correlation between cervical muscle force and the lift test (r=.50, P<.0001). Lifting ability is another area addressed by the NDI and, therefore, we would expect a correlation with this measure.

In this study, FAR and the lift test were considered "functional" measures, implying that they measure some aspect of a person's ability to function. The FAR test measures a person's ability to rotate the head and thorax relative to the pelvis.15 This action is essential for the performance of many daily activities such as looking over one's shoulder or rolling from a supine position to a side-lying position. The test itself is akin to looking over one's shoulder while in a seated position. In support of its use as a functional measure, Schenkman et al14 found a strong association between FAR and tests of physical performance (functional reach, moving from a supine to a sitting position, and 360° turn). Lifting is another commonly performed daily activity. Lifting ability was assessed using the methods of Mayer et al.30 The protocol measures the ability to lift a load from approximately waist height to head height as might occur when placing an object on a shelf.

Some additional correlations are noteworthy. A moderate inverse relationship was noted between pain and cervical ROM. Intuitively, one would expect that the more pain a person has, the less he or she would be willing to move the cervical region. Hagen et al16 found a similar, but weaker, relationship in forest machine operators. The relationship between pain and FAR did not reach statistical significance, which suggests that the subjects were not limited by pain in their ability to rotate the entire spinal column. Perhaps the subjects compensated during FAR by requiring more relative mobility of the thoracic and lumbar regions of the spine. As expected, there was good correlation between the FAR test and cervical ROM (r=.65, P<.0001) because both measures address axial mobility. However, the correlation between the FAR test and the NDI was not as strong (r=–.41, P<.001). The fact that the FAR test correlates more strongly with an impairment measure compared with a disability measure suggests that the FAR test is a better measure of impairment than function. Further research is needed to clarify interpretation of FAR test results in this population. A moderate inverse relationship was also noted between pain and the lift test. The most common reason for terminating the lift test was pain that may have limited the subjects' ability to exert force. However, it has also been reported that patients with CSD have weaker cervical musculature.23,24 Either of these could have contributed to this relationship. In addition, it has been shown that incorporation of strengthening exercises for the cervical musculature in rehabilitation programs is associated with improvements in pain and disability.24,37,39

The relationship between the NDI and both the PCS and MCS found in our study is similar to that reported by Riddle and Stratford.17 In their study, correlations between the NDI and the PCS and MCS were .53 and .47, respectively. In that same study, relatively low correlations were noted between the NDI and cervical ROM measurements, whereas, in our study, higher correlations were noted. This could be because we used principal component analysis for cervical ROM or because we controlled for age, sex, and acuity.

We defined acuity as the amount of time since the onset of symptoms. Others have defined acuity in patients with CSD in a similar manner.39 A surprising finding, however, was that there was no overall relationship between acuity and the measured variables. The fact that there was no difference between groups suggests that defining acuity solely in this manner may not be appropriate. Other factors may need to be considered as well (eg, pain pattern, amount of limitation in ROM).

There was also no effect of payment type (managed care or fee-for-service) on the variables measured. This finding is consistent with those of other studies that have shown no differences in health status or health outcomes in patients provided with similar interventions covered by either type of insurance.40,41

As with any correlational study, statements regarding causality cannot be made. This study was cross-sectional in nature and merely evaluated the relationships between the various measures. Changes in the impairment, functional limitation, or disability measures followed prospectively would be useful and would provide data on the predictive ability of a given measure. Another limitation of our study is the lack of random sampling. Subjects were consecutively referred to one outpatient physical therapy clinic and, therefore, may not be representative of patients with CSD as a whole. Despite these limitations, our data may be useful for developing testable hypotheses. For example, which variables are most useful for predicting outcomes as a result of therapeutic intervention? More specifically, can a given impairment measure predict a functional outcome? Because improving function is often the primary goal of treatment, those impairment measures that are most closely related to the relevant function should be recorded and followed over the course of care. It may also be that the relationships among impairments, functional limitations, and disability are different for different pathologies. The subjects in our study included those with both radiating and nonradiating neck pain. No attempt was made to delineate these 2 groups because of the small sample size. Further study is needed using a larger sample to elucidate the nature of these relationships in patients with different pathologies.


   Conclusion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 Conclusion
References
 
The relationship among selected measures of impairment, functional limitation, and disability in patients with CSD was investigated. Positive correlations were noted between the 3 sets of measures in this population, thereby affirming the assumption that impairments, functional limitations, and disability are related. In addition, acuity (as defined by the amount of time since the onset of symptoms) had no effect on the recorded variables. There was likewise no influence on the variables when comparing patients with managed care or fee-for-service payment arrangements. Limitations of the study were addressed, and suggestions for future research were made.


   Footnotes
 
Concept/research design and writing were provided by Dr Hermann and Dr Reese; data analysis was provided by Dr Reese; and data collection, project management, fund procurement, and subjects were provided by Dr Hermann.

This study was approved by the Institutional Review Board for the Use of Human Subjects in Research at Texas A&M University.

This study was funded, in part, by a grant from the Orthopaedic Section, American Physical Therapy Association.

* Performance Attainment Associates, 3550 Labore Rd #8, St Paul, MN 55110. Back

{dagger} Chatillon, 8600 Somerset Dr, Largo, FL 33773. Back

{ddagger} Velcro USA Inc, 406 Brown Ave, Manchester, NH 03108. Back


   References
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 Conclusion
 References
 

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