Abstract
Background context
Ambulation limitation is the hallmark of impairment in lumbar spinal stenosis (LSS). Capacity and performance have been defined as two distinct aspects of disability. Previous literature suggests that a person’s walking capacity may not be reflected in their daily walking performance.
Purpose
To examine the relationship between survey instruments, tested walking capacity, and daily ambulatory performance in people diagnosed with LSS.
Design/Settings
Prospective laboratory and clinical observational study at a tertiary care spine clinic.
Patient Sample
12 subjects with LSS significant enough to be scheduled for epidural injection.
Outcome measures
Questionnaire (including the Swiss Spinal Stenosis Questionnaire, Pain Disability Index, Oswestry Disability Index, Quebec Back Pain Disability Scale, and SF-36), laboratory walk testing (walking capacity) and activity monitors (community ambulation).
Methods
Subjects filled out functional questionnaires; performed a Self-Paced Walking Test (SPWT) of up to 30 minutes; and wore an Actigraph activity monitor during waking hours for 7 days.
Results
There was no statistically significant relationship between walking capacity (SPWT) and community ambulation per day (activity monitors), however the maximum time of continuous activity during community ambulation had a strong relationship (r=0.63) with the SPWT. Fifteen self-report measures of ambulation were significantly correlated with the SPWT, activity monitor, or both. Of these, 13 (87%) were more highly correlated to the SPWT than the activity monitor. The SPWT test had a strong relationship (r>.60, p<.05) with global function scales, but community ambulation did not.
Conclusions
Walking capacity and walking performance in LSS appear to be different constructs. Survey instruments appear to reflect capacity rather than performance. This dissociation between walking capacity and performance has implications for the clinical management and outcomes assessment of people with LSS.
Keywords: Back pain, international classification of function, spinal stenosis, walking, functional capacity, participation, activity monitors
Introduction
One of the most fundamental measures of physical capacity and performance is ambulation. Walking is vital to many functions needed for everyday life. In addition, moderate physical activity has been shown to significantly reduce the risk of cardiovascular disease, thromboembolic stroke, and type 2 diabetes mellitus.1 Regular walking has also been shown to delay cognitive impairment in the elderly,2 improve sleep,3 and aid in the management of depression and anxiety disorders.4 It is clear that walking is critical to overall health, and thus limitation in everyday ambulation is a serious clinical indicator that needs to be monitored by patients and their doctors.
Walking limitations are a hallmark of lumbar spinal stenosis (LSS). Anatomically, LSS is characterized by a narrowing of the lumbar spinal canal or nerve root foramen. Clinically, people with LSS present with a variety of symptoms including back pain, neurological deficits and pain in the lower limbs.5;6 The cardinal symptom of LSS is neurogenic claudication, described as leg pain and or numbness, weakness and tingling that is exacerbated by walking, standing and lumbar extension.7 Such symptoms of LSS often lead to substantial disability,8 where activities requiring walking or prolonged standing are often avoided and health related quality of life is diminished.9–11
The discussion of disability related to LSS benefits from the common conceptual framework provided by the International Classification of Functioning, Disability and Health.12 One of the fundamental principles of the classification system is the difference between capacity (an individual’s ability to perform a given task or action in a controlled setting) and performance (the activities performed by an individual on a day to day basis in the context of their own life). The distinction between capacity and performance is essential to the study of the ambulatory disability caused by LSS.
Because walking limitations play such a central role in LSS, the adequate assessment of ambulation-related disability is critical. The primary methods used to assess walking can be grouped into three major categories: 1) questionnaires to assess patients’ perceived level of walking related disability,13–18 2) laboratory walking tests to determine ambulation capacity,19–23 and 3) community ambulation measured using activity monitors to assess walking performance in daily life.24–26 Traditionally, walking has been assessed in LSS populations using self report methods or objective tests of walking capacity in the laboratory setting. However, recent research has used activity monitors to measure daily physical activity of individuals from a variety of subject populations, including the elderly, stroke survivors, and cerebral palsy patients.18;27;28 The ability to measure duration and intensity of activity along with step counts has made activity monitors the gold standard in measuring physical activity for the purpose of medical research.24–26 Yet this method has received little attention in assessment of outcomes in LSS populations.
The purpose of the present study was to examine relationships between walking capacity and performance in people with LSS by comparing results of self-report questionnaires, a walking capacity test and activity monitoring of community ambulation. We hypothesized that self-reported walking disability would be more highly correlated with performance than with capacity.
Materials and Methods
Subjects
This was a prospective laboratory and clinical observational study which took place at a tertiary care spine clinic. Possible subjects were identified through review of the clinic schedule for epidural injections at the University of Michigan Spine Program. All patients scheduled for epidural injection during a consecutive three month period who were identified as eligible for our study were called on the phone and provided information about our study.
Inclusion criteria were age over 45 years and a clinical diagnosis of LSS by either a physiatrist or a surgeon. Diagnosis was based on review of patient history, physical examination, and confirmation of anatomical stenosis on MRI. All subjects were required to have documented symptoms of neurogenic claudication (e.g. pain, numbness, weakness or tingling in the lower extremity brought on by lumbar extension, standing or walking). All subjects had been referred for epidural injection to treat lumbar spinal stenosis. Stenosis may have been at single or multiple levels. Exclusion criteria included disk herniation and/or other comorbidities that would limit walking capacity. Specific co-morbidities warranting exclusion included any other disorder that might be a limiting factor in ambulation. Examples include severe osteoarthritis of the hip or knee, peripheral vascular disease, coronary artery disease, and chronic obstructive pulmonary disease. All patients scheduled for epidural injection during consecutive three month period who were identified as eligible for our study were called on the phone and provided information about our study. Subjects agreeing to participate were scheduled for meeting with research staff the week prior to their injection and guided through the informed consent process. This project was granted approval by the Institutional Review Board IRBMed at the University of Michigan.
Data Collection and Measures
At the initial meeting, subjects filled out a questionnaire, completed a walking test and were then given an activity monitor and instructed to wear it for 7 days prior to their epidural injection.
Self-Report Measures
The questionnaire included demographic information, history of back/leg pain, walking specific questions, and five global function scales including: the Quebec Back Pain Disability Scale,29 Pain Disability Index,30 Oswestry Disability Index, 18 and the Physical Function and Symptom Severity subscales of the Swiss Spinal Stenosis Questionnaire (SSSQ).31 The walking specific questions were: “How would you say your walking capacity is today, on a scale of 0 to 10, with 0 being your worst day, and 10 being your best day?”,“ I can walk ____ feet without a rest before I MUST stop” and “When I am forced to stop walking I stop because of pain in my legs”. These walking questions are meant to provide additional walking information which is not provided by the Swiss Spinal Stenosis Questionnaire and have been shown to be reliable and valid, using the Self Paced Walking Test as a criterion measure.34
The Quebec Back Pain Disability Questionnaire (QBPDS) was used to assess pain and disability resulting from back pain. In the QBPDS, patients rate the degree of difficulty from 0 (not at all difficult) to 5 (unable to do) for performing 20 various activities, such as sleeping, standing for 20–30 minutes, and walking several miles. A total score is calculated by summing all 20 responses, with a higher score representing greater back pain related disability. Test-retest reliability for the English version is reported to be 0.93, and internal consistency for the scale is 0.95.29
The Pain Disability Index (PDI) consists of 7 items used to measure a subject’s perceived level of disability across various facets of life, including self-care, social activity, and family responsibilities. Severity of disability for each domain is rated on a 0–10 visual analog scale, with a total maximum score of 70 points. A higher score represents higher pain related disability. Psychometric analysis of the PDI has supported its construct validity and reliability.30
The 5-item Physical Function Scale of the Swiss Spinal Stenosis Questionnaire (SSSQ) is used primarily to assess walking capacity. The score was calculated as the un-weighted mean of the five items in the scale. The resulting possible scores of 1–4 represent a range from mild to severe limitation in physical function/walking.31 The 7-item Symptom Severity Scale of the SSSQ was included to examine severity of symptoms related to LSS, and is scored as the un-weighted mean of the seven items in the scale, with scores from 1–7 representing a range from mild to very severe pain. Both scales have been found to be internally consistent, reliable and responsive to clinical change.15;31–34
The Oswestry Disability Index (ODI) is a 9-item questionnaire which assesses degree of back pain-related disability. Severity of pain and disability in activities such as walking, sitting, standing and personal care are rated on Likert scales of 5 or 6 points. The ODI was calculated as a percentage of the total possible score of 53, with a greater score representing greater back related disability.9;35 The ODI has repeatedly been shown to be a valid and reproducible measure of back-pain related disability and has been used specifically to evaluate walking in LSS populations.23;36
Overall health and disability was assessed using the 36 item Short Form Health Survey (SF-36).37 Each SF-36 question is categorized into one of the following scales: General Health, Physical Functioning, Social Functioning, Role Limitation – Physical, Role Limitation – Emotional, Mental Health, Energy/Fatigue, Pain, and Comparative Health. Each scale score is calculated independently using algorithms defined by the developers.37
Walking Test and Clinical Measures
After completing the questionnaire, subjects completed a Self-Paced Walking Test (SPWT).33 In the SPWT, walking capacity is measured as the distance a person is able to walk continuously on a flat surface at a self-selected pace until being forced to stop due to symptoms of LSS, including neurogenic claudication (i.e. pain, numbness, tingling, or weakness in at least one leg or buttock) and/or low back pain, up to a limit of 30 minutes. If patients reported stopping due to reasons other than LSS symptoms (e.g. general fatigue, shortness of breath or dizziness), this was recorded and the walking test data was excluded from analysis. The SPWT was developed for use as a criterion measure of walking capacity in LSS patients and has been shown to have high re-test reliability in this population.33 Subjects completed the SPWT along a flat hallway indoors or along the even surface of an outdoor parking lot. Time was kept using a stopwatch and distance was measured via a distance wheel (Stanley DMW40, New Britain, CT, USA) directly following the path of the subject. Immediately prior to and following the test, subjects completed 100mm visual analog pain scales (VAS) for their back and legs as well as a body diagram describing the type and location of symptoms (pain, tingling, numbness, weakness) experienced at that time. During the SPWT, subjects were asked to alert the research staff when symptoms of LSS first began. The nature and location of these symptoms were recorded along with any other symptoms experienced during the test and the symptoms causing termination.
Activity Monitors
Upon completion of the walking tests, subjects were provided with an activity monitor (Actigraph GT1M, Actigraph LLC, Pensacola FL, USA) to wear for 7 days. Subjects were instructed to wear the activity monitors from the time they woke up in the morning to the time they went to bed at night for 7 days prior to their epidural injection. Activity monitors were worn on an elastic band around the waist at the level of the hip bone. Subjects were told to remove the monitor only while showering or swimming. Subjects were also instructed how to complete a daily activity log which was used in analysis to assess monitor data integrity. Activity monitors were collected by research staff at the time of the subject’s epidural injection. The GT1M measures and records time varying accelerations 30 times per second to produce ‘activity counts’ and step counts over 60 second epochs. The activity score thresholds are defined based on algorithms developed by researchers specifically for the Actigraph and the counts are determined based on mathematical modeling programs within the Actigraph software. Anything less than or equal to an activity score of 100/minute is classified as sedentary. A score between 101/min to 1,952/min is defined as light intensity activity, with moderate intensity activity ranging from 1,953/min to 5,724/min, and heavy intensity activity defined as an activity score >5,725/min.38 The Actigraph is widely accepted in the field as a valid and reliable means of assessing ambulatory physical activity.39–44
Data analysis
Pearson product moment correlation coefficients were used to examine the strength of relationships between variables. In the case of nominal or ordinal variables, Spearman correlation coefficients were used. A p value of 0.05 was used to determine the significance of correlation. An r value of >0.80 was considered a very strong relationship, 0.60 – 0.79 a strong relationship, 0.40 – 0.59 a moderate relationship, and <0.40 a weak relationship.45;46
For the activity monitor, a new variable was designed: maximum time of continuous activity. This was defined as the maximum number of continuous minutes per day at or above light intensity activity (activity score >100/minute), with no more than one minute of activity below light intensity in between. The inclusion of bouts of activity with single minutes of no activity between is to allow for the normal stop and go nature of activity in one’s life. This was decided upon because in our other work with LSS patients, in response to a question addressing the amount of time needed to recover after being forced to stop walking due to pain, the minimum time recorded was 2 minutes. Therefore we determined that allowing for a single minute of relative inactivity was acceptable and reflective of the functional demands of community activity.
Results
Each of the twelve recruited subjects completed all three phases of testing, including the self-report measures, SPWT, and activity monitor. Subject non-compliance, scheduling difficulties, and one case of an activity monitor that lost power prevented us from collecting the full 7 days of activity data on 7 (58%) subjects. The minimum number of days of collected data was 4 days, with an average of 6.3±0.9 days per subject. All subjects reported terminating the Self-Paced Walking Test due to symptoms of LSS (neurogenic claudication and/or low back pain), none were limited by other diseases..
Basic demographic and descriptive data for the subject population can be seen in Table 1. Of the total sample, 75% were male and the mean age was 66.3±9.8 years. It should be noted that all but one of the subjects had a BMI in the overweight or obese range, with an average BMI of 33.4±7.8. The majority of subjects (83%) had either back or leg pain with rest, and 100% of subjects had both back and leg pain with walking. These symptoms are in keeping with the clinical diagnosis of LSS. Scores for the ODI and Physical Function Scale of the SSSQ are similar to those found in previous studies of walking in LSS.15;33;34
Table 1.
Subject demographics, clinical presentation, and self report measures (n=12)
| All Subjects (n=12) | Standard deviation |
Min | Max | |
|---|---|---|---|---|
| Age (years) | 66.25 | 9.8 | 53 | 81 |
| Gender, % Male | 75.0 | |||
| Body Mass Index (BMI) | 33.4 | 7.8 | 18.8 | 47.1 |
| Duration of symptoms (years) | 4.7 | 1.5 | 1 | 10.8 |
| Back pain at rest | 10 (83.3%) | -- | ||
| Back pain w/ walking | 12 (100%) | -- | ||
| Leg pain at rest | 10 (83.3%) | -- | ||
| Leg pain w/ walking | 12 (100%) | -- | ||
| VAS back, pre SPWT (mm) | 39.9 | 27.0 | 0 | 78 |
| VAS back, post SPWT (mm) | 45.3 | 26 | 5 | 82 |
| VAS pain leg, pre SPWT* (mm) | 30.1 | 23.2 | 0 | 62 |
| VAS pain leg, post SPWT* (mm) | 51.8 | 26.9 | 9 | 87 |
| Quebec | 48.2 | 16.8 | 21 | 74 |
| PDI | 28.8 | 8.1 | 15.2 | 47 |
| Swiss.PF | 2.51 | 0.38 | 2 | 3.2 |
| Swiss.SS | 2.31 | 0.52 | 1.1 | 3 |
| Oswestry (%) | 48.9 | 11.6 | 28.3 | 69.8 |
| SF-36: | ||||
| General Health | 55.3 | 22.4 | 15 | 87 |
| Physical Functioning | 25.8 | 19.9 | 5 | 60 |
| Social Functioning | 52.1 | 19.8 | 25 | 75 |
| Role Limited – Physical | 14.6 | 31.0 | 0 | 100 |
| Role Limited – Emotional | 36.6 | 43.7 | 0 | 100 |
| Mental Health | 59.3 | 23.3 | 4 | 84 |
| Energy/Fatigue | 42.1 | 18.3 | 0 | 65 |
| Pain | 30.3 | 16.4 | 0 | 62 |
| Comparative Health | 56.3 | 21.7 | 25 | 100 |
| Quality of Life** | 3.2 | 0.84 | 1 | 5 |
| Overall health** | 3.3 | 1.1 | 2 | 5 |
| Life satisfaction** | 3.2 | 0.83 | 2 | 5 |
Score of most painful leg was used
from SF-36
VAS = Visual Analog Pain Scale
SPWT = Self-Paced Walking Test
Quebec = Quebec Back Pain Disability Scale
PDI = Pain Disability Index
Swiss.PF = Physical Function Scale of the Swiss Spinal Stenosis Questionnaire
Swiss.SS = Symptom Severity Scale of the Swiss Spinal Stenosis Questionnaire
Oswestry = Oswestry Disability Index
The results from both the SPWT and activity monitor data can be seen in Table 2. Our data exhibits a wide range of both capacity and performance among our subject population. This reflects the variable nature of the impact of LSS on each individual. Table 3 illustrates correlations between the SPWT, activity monitor data, and self-report measures. A strong relationship (r=0.63, p<.05) was observed between distance on the SPWT and maximum time of continuous activity per day as measured by the activity monitor (r=0.63). A moderate relationship was observed between the SPWT and overall activity per day (r=0.53), but this was not statistically significant (p=.078).
Table 2.
Physical tests of capacity and performance (n=12)
| Mean | Standard Deviation | Min | Max | |
|---|---|---|---|---|
| SPWT Distance (m) | 775.8 | 725.6 | 60 | 2065 |
| SPWT Time (sec) | 840.4 | 690.2 | 67 | 1800 |
| SPWT Distance to1stsx (m) | 202.5 | 296.1 | 10 | 900 |
| Activity count/day (Actigraph activity count) | 99958.9 | 69224.7 | 21906 | 246249 |
| Max cont activity (min) | 26.5 | 12.8 | 7.5 | 46.14 |
| Steps/day | 2821.9 | 1996.8 | 790 | 6919 |
| Meters walked/day | 1687.7 | 1447.0 | 371.3 | 4912.5 |
SPWT = Self-Paced Walking Test
SPWT Distance to1stsx = Distance to the first onset of symptoms reported by the subject during the self-paced walking test
Table 3.
Relationships between questionnaires, capacity as measured by the self-paced walking test (SPWT), and performance (as measured by the activity monitor) in LSS p
| Item | Walking Capacity (SPWT) | Walking performance (activity monitor) |
Stronger correlation |
||
|---|---|---|---|---|---|
| SPWT Distance | SPWT Distance to 1st Symptoms |
Activity count/day |
Max continuous activity |
||
| SPWT Distance | 1 | .563 | .527 | .629* | ----- |
| SPWT Time to 1st Symptoms | .563 | 1 | −.075 | .344 | ----- |
| Activity count/day | .527 | −.075 | 1 | .879** | ----- |
| Max continuous activity | .629* | .344 | .879** | 1 | ----- |
| Quebec | −.638* | −.549 | −.065 | −.162 | Capacity |
| Oswestry | −.595* | −.310 | −.148 | −.070 | Capacity |
| Swiss PF | −.610* | −.427 | .015 | −.107 | Capacity |
| SF-36 PF | .825** | .325 | .521 | .500 | Capacity |
| Walking Capacity | .682* | .422 | .304 | .265 | Capacity |
| Estimated Walking | .886** | .659* | .470 | .541 | Capacity |
| Leg Pain | .492 | .216 | .623* | .754** | Performance |
| Quebec_Stand | −.551 | −.681* | −.069 | −.269 | Capacity |
| Quebec_Walk | −.755** | −.439 | −.175 | −.274 | Capacity |
| Quebec_Reach | −.650* | −.436 | −.291 | −.282 | Capacity |
| Quebec_Run | −.664* | −.151 | −.884** | −.825** | Performance |
| Quebec_Groceries | −.727* | −.628 | −.192 | −.375 | Capacity |
| Swiss.PF_Walk | −.715* | −.622* | −.249 | −.375 | Capacity |
| Swiss.SS_Weak | −.742** | −.463 | .127 | −.081 | Capacity |
| Swiss.SS_Balance | −.673* | −.646* | .057 | −.072 | Capacity |
P<0.05
P<0.01
Quebec = Quebec Back Pain Disability Scale
Swiss.PF = Physical Function Scale of the Swiss Spinal Stenosis Questionnaire
Swiss.SS = Symptom Severity Scale of the Swiss Spinal Stenosis Questionnaire
Oswestry = Oswestry Disability Index
SF-36 PF = SF-36 Physical Functioning
Walking capacity = Response to this question: “How would you say your walking capacity is today, on a scale of 0 to 10, with 0 being your worst day, and 10 being your best day?”;
Estimated distance = Response to this question: “I can walk ____ feet without a rest before I MUST stop”
Leg Pain = Response to this question: “When I am forced to stop walking I stop because of pain in my legs”.
Quebec_Stand = Difficulty rating for standing up for 20–30 minutes
Quebec_Walk = Difficulty rating for walking several miles
Quebec_Reach = Difficulty rating for reaching up to high shelves
Quebec_Run = Difficulty rating for running two blocks
Quebec_Groceries = Difficulty rating for carrying two bags of groceries
Swiss.PF_1= Rating for walking distance
Swiss.SS_6 = Rating for severity of leg and foot weakness
Swiss.SS_7 = Rating for severity of balance problems
Fifteen self-report measures were found to have statistically significant correlations with the SPWT test, activity monitor (maximum time of continuous activity), or both. Of these 15 measures, 13 (87%) were more highly correlated to the SPWT than the activity monitor. The SPWT test had a strong relationship (r>.60, p<.05) with the Quebec Back Pain Disability Scale, Swiss Spinal Stenosis Physical Function Survey, and Oswestry Disability Index, as well as the SF-36 Physical Functioning Scale, estimates of maximum distance without stopping, and weakness in the legs and feet.
The activity monitor data was significantly correlated with only two outcome measures. Walking limited by pain in the legs exhibited a strong relationship to both average activity per day (r=0.623, p<.05) and maximum continuous activity per day (r=0.754, p<.01). Both average activity per day and maximum continuous activity per day had a very strong relationship (r=0.885 and r=0.885 respectively, p<.01) with question #12 on the QBPDS, in which subjects were asked to rate the difficult of running two blocks.
Discussion
This was the first study of its kind to examine the relationship between walking capacity and performance in people with LSS. A strong relationship was demonstrated between laboratory based walking capacity and maximum daily continuous activity measured with an activity monitor. A moderate, yet non-significant relationship was observed between walking capacity and average daily community ambulation. Questionnaires commonly used to evaluate walking in patients with LSS were shown to be mostly associated with capacity, not performance. This research also developed the activity monitor parameter of maximum continuous daily activity, which proved to be more highly correlated with walking capacity than any other measure of community-based activity.
The strengths of this study include the use of multiple, well-validated questionnaires to assess self-reported walking disability. The reliability of collected data was strengthened via use of the SPWT and the extended period of time (7 days) in which the subjects were instructed to wear the activity monitor. Limitations of this study include sample size, incomplete follow-up data, and non compliance. A lack of variation in gender and BMI among our study population may provide a degree of sampling error. Diagnostic criteria for stenosis, and thus inclusion criteria for this study, can be debated. The relationship between radiological stenosis and clinical symptoms has been seriously challenged by a number of studies.47 A recent study has shown important disagreement between expert surgeons as to the presence of neurogenic claudication among persons who have been offered surgery for spinal stenosis.48 However in keeping with current convention, a clinical diagnosis of LSS, including presence of neurogenic claudication, with anatomical stenosis confirmed on MRI, was used. Likely the population represented persons whom other reasonable clinicians would believe have spinal stenosis.
Participants in this study had lower average daily step counts than previous studies of older adults.25;49 Compared to research by Cavenaugh et al. 25 subjects in the current study had a markedly lower average daily step count (2821.9 steps/day) than both healthy older adults (9,981.7 steps/day) and older adults with ‘functional limitations’ (7,681.5 steps/day). This finding is a reminder of the severe compromise in life function imposed by clinical spinal stenosis.
This study provided new insight into the relationship between capacity and performance in LSS. Recent research by Zalewski et al.49 found that in residents of a critical care retirement community there was no relationship between performance on a clinic-based tests of walking capacity and community based walking performance. The results of the present study, however, did demonstrate a significant association between walking capacity and performance; Capacity to walk in the lab was observed to be significantly correlated with the average daily bout of maximum continuous activity in the community.
Though our results showed a correlation between walking capacity and performance in patients with LSS, our findings also suggest that walking capacity and performance are not the same, and as such should be treated as two separate entities. Maximum time of daily continuous activity appeared to be representative of walking capacity, but the more global measure of walking performance (average daily activity) was not significantly related to lab-based walking capacity. This difference between capacity and performance appears to be of vital importance to the interpretation of questionnaires commonly used to assess the disability level of people with LSS. Our data shows that self-report measures used in this study are an indicator of capacity, not performance. Therefore, the data elicited by these questionnaires gives an incomplete, and possibly misleading, picture of a patient’s level of disability.
This apparent discrepancy between walking capacity and performance has implications for both clinical practice and research related to treatment and assessment of mobility in LSS. The functional goal of interventions for LSS is thought to be improvement in performance, not capacity. A person who is made more capable of walking but does not take advantage of that capacity via increased performance will neither have an improvement in quality of life nor reap the well-documented benefits of walking participation on overall health.
Spinal stenosis is defined as an anatomical and physiological disorder. However, its impact on people’s lives is multidimensional. As such, a single mode of treatment for LSS cannot be assumed to improve all facets of the disease. Treatments for LSS are commonly based on capacity; a treatment is deemed successful if the patient’s ability to walk is improved. But if as mentioned, this improvement in capacity is not met with an improvement in performance (i.e. the actual walking done by the patient) then the patient’s participation in daily activities and quality of life has gone unchanged. Thus, the treatment of patients performing under their capacity level will not result in a significant increase in daily activity levels unless the limiting factors to performance, whether they be physical, social, or psychological, are identified and subsequently addressed. A multidisciplinary assessment and perhaps multidisciplinary treatment of spinal stenosis patients may result in better outcomes.
In terms of research and outcomes assessment, this study shows that even a single function such as ambulation has many dimensions that cannot be measured using a single test or survey. If we are using outcome tools focusing on capacity (such as the SPWT or self-report tools), we may be missing the important impact or lack of impact on patients’ day to day lives (performance). Activity monitors as used in the current study should be considered in future research with LSS patients, especially when trying to define the effects of interventions. Research into the nature of participation deficits and the factors (such as high BMI) that may lead to such deficits may result in interventions that are more specific to the actual problem of the patient. A larger database of ambulation profiles of persons with spinal stenosis will help us understand how capacity limitations affect participation and how people adapt to those limitations.
Finally, this data suggests that activity monitors may become useful in measurement of function in the clinical setting. It is possible that, in the future, the criteria for surgical intervention for spinal stenosis would include a drop in weekly activity below a certain level or a slope of decline that suggests that surgery is the better choice. A poor relationship between capacity and participation may alert the clinician that a multidisciplinary approach is needed.
Conclusion
There is a relationship between capacity to walk and actual performance in walking in the community, but it is not exact. Questions about ambulation on most standardized outcome tools appear to relate best to capacity, yet performance and participation are the more important life goals. This difference highlights the need for researchers to use tools such as activity monitors to measure participation as an ultimate outcome measure, and for clinicians to focus on the multifaceted barriers that exist between improved capacity and improved performance in daily life.
Footnotes
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