Volume 87, Issue 9 , Pages 1250-1256, September 2006
Disability in Patients With Degenerative Lumbar Spinal Stenosis
Article Outline
Abstract
Lin S-I, Lin R-M, Huang L-W. Disability in patients with degenerative lumbar spinal stenosis.
Objective
To determine factors associated with disability in patients with degenerative lumbar spinal stenosis.
Design
One-group cross-sectional study.
Setting
University hospital.
Participants
One hundred eight patients with degenerative lumbar spinal stenosis.
Interventions
Not applicable.
Main Outcome Measures
Oswestry Disability Index and 4 categories of factors, including patient demographics (age, sex, number of comorbidities, medications), symptom-related factors (intensity, location, onset duration, neurogenic claudication), body structure and function as described in the International Classification of Functioning, Disability and Health model (muscle strength, vibration sense, spine flexibility), and stenotic condition (type and number of spinal segments involved).
Results
Patients with symptoms in both back and leg reported greater disability than those with symptoms only in the leg or back (P=.008). Greater disability correlated significantly with greater symptom intensity (r=.385, P<.001) and higher vibration threshold (r=.236, P=.014). While controlling the variance in patient demographics in the regression analysis, vibration sense and symptom location each added 10% of the variance in disability, and symptom intensity and strength each added 5%, with a total of 44% variance explained (P=.044).
Conclusions
Symptom intensity and location, vibration sense, and muscle strength were identified as significant factors and, together with patient demographics, accounted for 44% of the variance explained in disability. Further investigations are needed to determine if causal relationships exist between these factors and disability.
Key Words: Disability evaluation , Rehabilitation , Sensation , Spinal stenosis
LUMBAR SPINAL STENOSIS is a condition characterized by narrowing of the spinal canal, nerve root canals, or intervertebral foramina, and can lead to compression of the cauda equina or nerve root.1, 2 Pain is typically the primary complaint and also the main reason for seeking medical attention.1, 3, 4, 5, 6 In addition, signs of neurologic involvement due to nerve compression, such as reduced deep tendon reflexes, sensory impairments, and muscle weakness, are common.4, 6, 7, 8, 9 Degenerative lumbar spinal stenosis, which occurs mostly in adults more than 50 years old, has been noted as the most common indication for lumbar spinal surgery in the elderly in the United States,10 and is reported to be associated with substantial health care costs.11, 12
In addition to pain and neurologic involvement, poor standing balance, difficulty in rising from a seated position, and limitation in activities of daily living (ADLs) are common in patients with degenerative lumbar spinal stenosis.4, 6, 8, 9, 13, 14 Most alarming is that a majority of patients report mild to high levels of disability.6, 15, 16, 17 Thus, disability appears to be a common problem and therefore needs to be addressed clinically. A better understanding of the factors associated with disability might provide information that could lead to the development of more effective preventive and intervention strategies.
Patients generally believe that limitation in functional capacity is related to the severity of their symptoms. Research findings, however, only partly support this belief. In an early retrospective study9 that used information obtained from clinical records of, or mailed questionnaires from, 148 patients, pain intensity explained 18% of the variance in physical functional performance. A more recent study18 of 50 patients from our laboratory, in which we used standardized quantitative measures, found that pain intensity explained 17% of the variance in disability. These findings indicate that pain severity is only moderately associated with disability. It is unclear whether there would be a greater association if other symptom-related factors, such as neurogenic claudication and location of the symptoms, were also considered.
In addition to symptom-related factors, nonsymptom-related factors have also been associated with disability. A study4 that used clinical rank-order measures to test the physical function of 43 patients with degenerative lumbar spinal stenosis showed that severe pain, together with female sex and impaired balance ability, were successful in identifying 81% of patients with severe walking difficulty. Comorbidity, neuromuscular impairments, and sensory dysfunction or impairment have also been associated with disability.9, 18
Although some factors that contribute to disability have been identified, our understanding of these issues is incomplete. Previous studies have been limited by a lack of standardized measurements9 or by small sample sizes.4, 18 What is more, there is a lack of comprehensive research into many of the contributing factors to disability and their interactions. In this study, by using standardized quantitative measures of multiple dimensions of potential contributing factors and a fairly large sample size, we sought to identify factors associated with disability in patients with degenerative lumbar spinal stenosis.
Methods
Participants
Subjects were recruited from a spine clinic in a tertiary care hospital. The diagnosis was made by an orthopedic physician with more than 20 years of clinical experience. The diagnostic criteria were: more than 50 years old, with low back and/or leg pain for more than 1 month, with neurogenic claudication or exacerbation of pain with lumbar extension, and radiologic findings (magnetic resonance imaging [MRI], radiography) indicating central or lateral compression of the cauda equina. A total of 125 consecutive patients met the inclusion criteria and were interviewed by a researcher who used structured forms to obtain information about medical and surgical history, comorbidity, and medications. Systematic reviews of medical charts were also conducted to confirm the patients’ self-reports. Two trained researchers, both physical therapists, conducted all the interviews, tests, and data extraction. Patients with the following conditions were excluded: previous lumbar spine surgery, painful musculoskeletal conditions in the lower extremity (eg, arthritis, gout), and a history of central nervous system lesions that could affect functional performance (eg, stroke, Parkinson’s disease). Seventeen patients were excluded because of previous lumbar surgery, painful arthritis, stroke, traumatic brain injury, Parkinson’s disease, and marked leg-length discrepancy combined with hip pain. A total of 108 patients participated in the study.
This study was approved by the institutional review board of the hospital where the research was conducted. All the subjects gave their informed consent.
Disability
We used the Oswestry Disability Index (ODI), which is a condition-specific measurement of how pain affects ADLs, to measure disability.19, 20 Percentage scores (relative to the maximal applicable scores) were used for data analysis. The higher the score, the greater the disability reported by the patient. This questionnaire has been shown to have high reliability and validity.15, 16, 19, 21
Associated Factors
Four categories of potential factors, including patient demographics (age, sex, number of comorbidities and medications), stenotic condition (type and number of spinal segments involved), symptom-related factors (onset duration, intensity, location, neurogenic claudication), and body structure and function as described in the International Classification of Functioning, Disability and Health22 (muscle strength, vibration sense, spine flexibility) were investigated. Information about number of comorbidities and medications was obtained through structured questionnaires and systematic review of medical charts.
Stenotic conditionMRI was used to classify lumbar stenosis into central, lateral, or combined types.23, 24, 25, 26 Central stenosis was defined as when the central canal and thecal sac became flattened ovals or triangular in shape, with obliteration of cerebrospinal fluid in the axial view. Lateral stenosis was defined when there was a loss of tail of fat shadow in the sagittal view, or trefoil narrowing of the lateral recess, or angular pinch-like encroachment of the lateral margin of the canal with obliteration of cerebrospinal fluid surrounding the nerve root in the axial view. A combined type was diagnosed in the prescnce of both central and lateral stenosis. Each patient’s MRI was viewed by a radiologist and an orthopedic surgeon, who were unaware of the nature of this study, or of the interpretation made by the other. When classifications differed, a consensus was reached through a meeting of the referring physician, the radiologist, and the orthopedic surgeon.
Symptom-related factorsWe evaluated symptom intensity with a visual analog scale (VAS), with 0 indicating no pain and 10 indicating the worst pain. In this evaluation, patients were asked to draw a vertical line on a 10-cm horizontal line to indicate the intensity of their worst pain within the past month. The distance between the zero point and the vertical line was used to indicate symptom intensity. The reliability of the VAS is high.27 Self-reported location of the symptom was classified as back only, leg only, or both. Positive neurogenic claudication was defined as exacerbation of pain in the buttocks and/or legs resulting from prolonged standing or walking, and relief of the symptoms from lying, sitting, or back bending.1, 2
Body structure and functionWe assessed muscle strength, vibration sense, and spine forward-bending flexibility to represent body structure and function. Isometric strength of bilateral hip flexion, knee extension and flexion, and ankle dorsiflexion was measured using a hand-held dynamometera with standardized testing procedures.28 Hip flexion, knee extension, and ankle dorsiflexion were tested with the patients seated in an elevated chair, trunk upright, and knees bent over the edge of the table. For hip flexion, patients were asked to raise the thigh about 7.6cm (3in) from the table; the dynamometer was placed at the anterior thigh above the knee joint. For knee extension, patients raised the knee to near full extension and the dynamometer was placed against the lower leg above the ankle. Ankle dorsiflexion was tested at approximately 20° of dorsiflexion, with the dynamometer placed at the dorsum of the foot above the metatarsal bones. For knee flexion strength, patients were positioned prone with the knee bent at 50° to 70° and the dynamometer placed against the lower leg immediately above the calcaneus. The interrater reliability of the Nicholas hand-held dynamometer on the strength of the knee muscles of a similar group of patients has been shown to be high.29 For hip and ankle strength in other populations, hand-held dynamometer measurement has also been shown to have high test-retest reliability30, 31, 32, 33, 34, 35 and validity.36 The ability to detect an externally applied vibration was tested to represent vibration sense. Three sites were tested: the first metatarsal head, lateral malleolus, and tibial tuberosity; we used a vibrameterb that delivers vibration at 120Hz, with adjustable amplitudes. The test was conducted with subjects in the supine position and the vibration amplitude was increased gradually by the researcher until the patient indicated verbally that the vibration was clearly perceived. A finger-to-floor test, which required the patient to bend forward as far as possible while standing barefoot, was used to measure the flexibility of the spine. The vertical distance between the tip of the middle finger and the floor was recorded. This test has excellent reliability and criterion validity (when compared with radiographic analysis).37, 38
Statistical Analysis
We used the computer software package, SPSSc for Windows for statistical analyses. For muscle strength (normalized to body weight) and vibration sense, we used the means of the 2 legs for data analysis. Analysis of variance (ANOVA) was conducted on disability for categorical factors that had more than 3 levels, such as age by sex (3 age groups: <60, 60–69, ≥70y), number of comorbidities (4 groups: 0, 1, 2, ≥3), number of medications (3 groups: 0–2, 3, >3), symptom location (3 groups: back only, leg only, both), stenotic type (3 groups: central, lateral, combined), and number of stenotic segments (4 groups: 1, 2, 3, >3). Tukey post hoc tests were conducted when ANOVA showed significant effects. Independent t test was conducted for claudication (2 levels: present, absent). The Spearman’s rank correlation was conducted between disability and all the continuous measurements.
We conducted a blockwise (hierarchical) regression analysis to determine what factors contributed to disability. The rationales for using hierarchical regression were that this model allowed for factors of different categories to be entered sequentially on a theoretical basis, and for the control variables to be forced to remain in the equation. The first block entered in the regression was “patient demographics,” including age, sex, and number of comorbidities and medications. These are factors that patients have little or no ability to control. All variables in this block were forced entered and remained in the equation to serve as control variables. The second block entered was “symptom-related factors” (onset duration, intensity, location, claudication) because they are believed to interfere with ADLs. “Body structure and function” (muscle strength, vibration sense, spine flexibility) was entered as the third block because these factors are important in movement performance. “Stenotic condition” (type of stenosis, number of segments involved) was the last block entered because its association with symptoms or outcome remains controversial.1, 13, 39, 40, 41, 42, 43 Stepwise selection, with the criteria for entering and removal as P values smaller than .05, and larger than 0.1, respectively, were used for blocks 2 to 4 to allow for competition for additional explained variability within each block. Categorical variables, including sex, symptom location, claudication, stenotic type, and number of segments involved, were dummy-coded before being entered into the equation. For muscle strength and vibration sense, we did a principal component analysis separately to generate factor scores for use in the regression analysis to reduce the number of independent variables. Statistical significance was set at α level of less than .05.
Results
Patients varied markedly in their demographics and symptoms (Table 1, Table 2), as well as in disabilities (Fig 1, Fig 2). The numbers of comorbidities and medications reported by the patients were also variable (see table 2). Results of ANOVA and t tests showed that the only significant factor was symptom location (fig 3): patients with symptoms in both back and leg had greater disability than those with symptoms in the back only (table 3). Relationships between disability and potential associated factors are shown in table 4. Greater disability was significantly related to greater symptom intensity and higher vibration threshold at the lateral malleolus.
Table 1. Disability, Patient Demographics, Pain, Vibration Threshold, Strength, and Spine Flexibility
| Item | Mean ± SD | Range |
|---|---|---|
| Disability (ODI) (%) | 31±16 | 3–73 |
| Age (y) | 63.6±10.71 | 50–82 |
| Onset duration (mo) | 23.6±43.6 | 1–240 |
| Symptom intensity (VAS) (cm) | 5.6±1.8 | 0.8–10 |
| Strength (% body weight) | ||
 Hip flexion | 49±15 | 12–85 |
| Knee flexion | 28±9 | 13–51 |
| Knee extension | 49±20 | 14–126 |
| Ankle dorsiflexion | 44±15 | 13–102 |
| Vibration sense (μm) | ||
| First metatarsal head | 4.39±4.73 | 0.54–31.71 |
| Lateral malleolus | 4.70±3.78 | 0.53–27.57 |
| Tibial tuberosity | 4.86±5.287 | 0.36–28.40 |
| Spine flexibility (finger-to-floor distance) (cm) | 21.65±14.9 | 0.0–54.7 |
Table 2. Frequency Counts for Patient Demographics, Stenotic Conditions, and Symptom-Related Factors
| Item | No. of Patients |
|---|---|
| Age | |
| 50−59y (fifth decade) | 37 |
| 60−69y (sixth decade) | 39 |
| ≥70y (seventh decade) | 24 |
| Sex (female) | 82 |
| Comorbidities (n) | |
| 0 | 18 |
| 1 | 40 |
| 2 | 32 |
| >2 | 18 |
| Medications (n) | |
| 0 | 5 |
| 1 | 4 |
| 2 | 8 |
| 3 | 36 |
| >3 | 38 |
| Not available | 17 |
| Type of stenosis⁎ | |
| Central | 18 |
| Lateral | 13 |
| Combined | 70 |
| Stenosis segments (n) | |
| 1 | 41 |
| 2 | 37 |
| 3 | 24 |
| 4 | 6 |
| Neurogenic claudication (positive) | 79 |
| Symptom location | |
| Back | 16 |
| Leg | 19 |
| Back and leg | 73 |
⁎ Based on MRI. Seven patients did not have MRI. |
Fig 1.
Disability in patients of different age, comorbidity, and medication groups. None of the within-group differences were significant.
Fig 2.
Disability in patients in different symptom groups. The only significant within-group difference was found between patients with primary symptoms in the back and those with symptoms in both the back and leg.
Fig 3.
Distribution of disability in patients with different symptom locations.
Table 3. Statistics for ANOVA and t Test on Disability
| Factors | P | Significant Pairwise Comparison |
|---|---|---|
| Age by sex | ||
| Age | .135 | |
| Sex | .279 | |
| Age by sex | .471 | |
| Comorbidity | .421 | |
| Medication | .103 | |
| Symptom location⁎ | .005 | Group (both) > group (back) |
| Claudication (t test) | .828 | |
| Stenotic type | .747 |
⁎ Group (both): symptom in both back and leg; group (back): symptom in back only. |
Table 4. Spearman Correlation Coefficients Between Disability and Potential Associated Factors
| Factors | Disability |
|---|---|
| Age | .088 |
| Onset duration | .039 |
| Symptom intensity | .417⁎ |
| Spine flexibility | .121 |
| Hip flexion strength | −.156 |
| Knee extension strength | −.072 |
| Ankle dorsiflexion strength | −.025 |
| Knee flexion strength | −.143 |
| First metatarsal head vibration | .185 |
| Tibial tuberosity vibration | .048 |
| Lateral malleolus vibration | .202† |
⁎ P<.01. |
† P<.05. |
Principal component analysis of strength (4 muscles) and vibration (3 sites) variables each resulted in 1 factor being extracted (for muscle strength: eigenvalue=2.731, percentage of variance=54.6; for vibration: eigenvalue=2.698, percentage of variance=76.6). The factor scores for strength and vibration thresholds were then used for regression analysis.
Five models emerged from the regression analysis (table 5). The first equation showed that the control variables (patient demographics) explained a small and nonsignificant amount of variance. An additional 10% of variance was explained when symptom location (both back and leg) was entered in the second equation. In the third equation, symptom intensity was selected and added another 5% of variance. A larger increment in R2 (.104) occurred when vibration sense was entered in the fourth equation. Adding strength factor scores in the fifth equation continued to increase the R2 significantly. The final equation selected (fifth equation) explained a total of 44% of variance and yielded 4 significant factors: symptom location, symptom intensity, vibration sense, and muscle strength (table 6).
Table 5. Models From Regression Analysis for Disability
| Model | R2 | Adjusted R2 | P | Factors Added |
|---|---|---|---|---|
| 1 | .145 | .087 | .052 | Age, female, number of comorbidities and medications |
| 2 | .243 | .177 | .008 | Symptom location (both back and leg) |
| 3 | .293 | .219 | .048 | Symptom intensity |
| 4 | .397 | .322 | .003 | Vibration sense factor score |
| 5 | .44 | .359 | .044 | Strength factor score |
Table 6. Statistics for the Final Selected Model (fifth equation) of Regression Analysis for Disability
| Factors Included | Standardized Coefficients (β) | P |
|---|---|---|
| Age | .085 | .48 |
| Female | .133 | .287 |
| Comorbidity | .127 | .251 |
| Medication | .012 | .913 |
| Symptom location: both back and leg | .237 | .038 |
| Symptom intensity | .327 | .005 |
| Vibration sense | .339 | .003 |
| Strength | −.249 | .044 |
Discussion
Problems arising from degenerative lumbar spinal stenosis are multidimensional and can predispose patients to disability. Before the exact cause(s) of disability can be identified and interventions designed, a better understanding of its associated factors is needed. Patients in this study reported a wide range of disability scores, from minimum (3%) to severe (73%), that were comparable to those reported previously.14, 15 On average, the mean disability score was 31%, indicating moderate disability and problems with sitting, lifting, and standing.18 Low but significant correlations were found between disability and symptom intensity, and vibration sense. And these 2 factors, together with symptom location and muscle strength, were significantly associated with disability.
Although age is believed to be associated with deterioration in functional capacity, it did not correlate significantly with disability. Specifically, we found that older patients (in their seventh decade or older) did not have greater disability than their younger counterparts. These findings agree with those of 2 previous studies that investigated patients from 50 to 90 years old,8, 9 and add evidence that strengthens the notion that age is not a key determinant in the extent of disability experienced by the patients.
What we found to be associated with disability were symptom-related factors, namely, intensity and location. It was not surprising to find that symptom intensity was significantly related to disability, because similar results have been reported.9, 18 What was surprising was that symptom location not only differentiated patients with different levels of disability, but also added a greater amount of explained variance than symptom intensity did in the regression analysis. The notion that pain location can be a relevant factor in functional capacity is supported by the significantly lower physical function level in patients with pain in the lower leg than in those patients whose pain did not reach the lower leg.6 Although statistical significance does not equal clinical relevance, the possibility that symptom location may deserve special attention clinically, at least in regard to disability, should not be overlooked.
Neurogenic claudication, a symptom reported in the literature to occur in 62% to 96% of patients with degenerative lumbar spinal stenosis,3, 9 was found in 73% of the patients in this study. This problem is a unique feature of this disease and is characterized by worsening of the symptoms from prolonged standing or walking that is believed to induce narrowing of the spinal canal.1, 2, 3, 44, 45 Yukawa et al17 reported that 94% of the patients with neurogenic claudication showed positive results from treadmill walking provocation test. Thus, intuitively this problem could be a primary factor in the limitation of daily activities. The present study, however, found that patients with neurogenic claudication did not report greater disability than those without, and the presence of this problem was not a significant factor. It is probable that the association between neurogenic claudication and disability was not high because most of the items in the ODI did not involve prolonged standing or walking.
Two factors in the body structure and function category, vibration sense and muscle strength, were identified as significant, with each adding 10% and 5% of variance explained, respectively. In a recent study6 in which clinical rank-order measurements were used, leg muscle strength and vibration sense showed a nonsignificant association with functional ability (as measured with the Medical Outcomes Study 36-Item Short-Form Health Survey). The discrepancy could possibly be related to differences in the sensitivity of the strength and sensory function measurements between the 2 studies. The issue of vibration sense deserves special attention because it reflects the integrity of the proprioceptive nervous system, whose function is crucial in providing sensory feedback during the performance of motor tasks.46, 47, 48, 49 Changes in vibration sense are typically subtle, however, and patients may fail to notice or report this problem. Also, the extent of this problem does not necessarily correlate with the severity of the disease. In addition to nerve root compression caused by stenosis, nonstenosis-related factors, such as the normal aging process or polyneuropathy,50, 51, 52, 53 can also cause impaired vibration sense. Thus, it is recommended that vibration sense be evaluated thoroughly in clinical management.
As for the stenotic condition, 2 studies13, 17 found that patients with lateral stenosis had less limited walking capacity than those with central stenosis. Other studies,1, 39, 41, 42 however, showed no significant differences between patients with different types of stenosis, or different numbers of spinal segments involved. Our findings support the latter. It has been suggested that nerve fibers may adapt differently to compression or structural changes over time and result in variations in clinical manifestation or presentation.54 Thus, the evidence so far suggests that stenotic condition, at least in terms of type and number of spinal segments involved, does not reflect the extent of problems experienced by the patients, and is not associated with disability.
Conclusions
The individual factors we investigated in this study had a low correlation with disability. Symptom intensity and location, vibration sense, and muscle strength were identified as significant factors and, together with patient demographics, accounted for 44% of the variance in disability. Specifically, patients with symptoms in both the back and leg, and with poorer vibration sense, were more likely to report greater disability. Further studies are needed to determine whether there is a causal relationship between these factors and disability.
Suppliers
Acknowledgment
We thank Po-Rong Lin and I-Jung Tsai for help in data collection.
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Supported by the National Science Council, Taiwan.No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.
PII: S0003-9993(06)00473-4
doi:10.1016/j.apmr.2006.05.021
© 2006 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.
Volume 87, Issue 9 , Pages 1250-1256, September 2006
