The Spine Journal 11 (2011) 816–823

Clinical Study

Walking assessment in people with lumbar spinal stenosis:capacity, performance, and self-report measures

Justin Conway, BAa, Christy C. Tomkins, PhDb, Andrew J. Haig, MDa,*aDepartment of Physical Medicine and Rehabilitation, University of Michigan, 325 E. Eisenhower, Ann Arbor, MI 48108, USA

bDepartment of Physical Education and Recreation Studies, Mount Royal University, 4825 Mount Royal Gate SW, Calgary, AB, T3E 6K6, Canada

Received 9 March 2010; revised 12 July 2010; accepted 29 October 2010

Abstract BACKGROUND CONTEXT: Ambulation li

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doi:10.1016/j.spinee.2

mitation is the hallmark of impairment in lumbarspinal stenosis (LSS). Capacity and performance have been defined as two distinct aspects of dis-ability. Previous literature suggests that a person’s walking capacity may not be reflected in theirdaily walking performance.PURPOSE: To examine the relationship between survey instruments, tested walking capacity, anddaily ambulatory performance in people diagnosed with LSS.STUDY DESIGN/SETTING: Prospective laboratory and clinical observational study at a tertiarycare spine clinic.PATIENT SAMPLE: Twelve subjects with LSS significant enough to be scheduled for epiduralinjection.OUTCOME MEASURES: Questionnaire (including the Swiss Spinal Stenosis Questionnaire,Pain Disability Index, Oswestry Disability Index, Quebec Back Pain Disability Scale, and 36-ItemShort Form Health Survey), 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 walking hours for 7 days.RESULTS: Therewas no statistically significant relationship betweenwalking capacity (SPWT) andcommunity ambulation per day (activity monitors), however, the maximum time of continuous activ-ity during community ambulation had a strong relationship (r50.63) with the SPWT. Fifteen self-report measures of ambulation were significantly correlated with the SPWT, activity monitor, or both.Of these, 13 (87%)weremore highly correlated to the SPWT than the activitymonitor. The SPWThada strong relationship (rO0.60, p!.05) with global function scales but community ambulation did not.CONCLUSIONS: Walking capacity and walking performance in LSS appear to be differentconstructs. Survey instruments appear to reflect capacity rather than performance. Thisdissociation between walking capacity and walking performance has implications for the clinicalmanagement and outcomes assessment of people with LSS. � 2011 Elsevier Inc. All rightsreserved.

Keywords: Back pain; International classification of function; Spinal stenosis; Walking; Activity monitors

status: Not applicable.

: JC: Nothing to disclose. CCT: Nothing to disclose.

ents: Rehabilitation Team Assessments (1 share,

sulting: Mainstay Medical (Financial). Other Rela-

ors, Inc. (Financial), The Center for Healthcare

rmation (Financial).

can be found on the Table of Contents and at www.

e.com.

uthor. Department of Physical Medicine and Reha-

of Michigan, 325 E. Eisenhower, Ann Arbor, MI

4) 763-4200; fax: (734) 615-1770.

ndyhaig@umich.edu (A.J. Haig)

nt matter � 2011 Elsevier Inc. All rights reserved.

010.10.019

Introduction

One of the most fundamental measures of physicalcapacity and performance is ambulation. Walking is vitalto many functions needed for everyday life. In addition,moderate physical activity has been shown to significantlyreduce the risk of cardiovascular disease, thromboembolicstroke, and type 2 diabetes mellitus [1]. Regular walkinghas also been shown to delay cognitive impairment in theelderly [2], improve sleep [3], and aid in the managementof depression and anxiety disorders [4]. It is clear that

ContextPatients with neurogenic claudication secondary to lum-

bar spinal canal stenosis sometimes present with com-

plaints of difficulty walking. Self-report outcome metrics,

an observed walking test, and newer remote surveillance

technologies have all been proposed to quantify this aspect

of the clinical problem. The authors compared patient-

reported functional outcome measures with laboratory

walking capacity testing and community ambulation

monitoring.

ContributionThe authors found that questions about ambulation in

commonly used self-reported assessment tools better

reflect ‘‘capacity’’ (how much a person can walk on de-

mand) as opposed to performance (how much they will

routinely walk daily). While interventions may be in-

tended to increase community performance, the more

commonly used metrics may be poor measures of that

outcome.

ImplicationAll attempts to measure outcomes are limited by their

focus—the answers one gets are greatly influenced by

the questions one asks. Accordingly, it is vital we ask

the right questions, and the authors have suggested that,

perhaps, we have failed to do so as it relates to ambula-

tion in stenosis. Involvement of patients’ values in set-

ting questions might be helpful as further measures

and objective outcome technologies are developed.—The Editors

817J. Conway et al. / The Spine Journal 11 (2011) 816–823

walking is critical to overall health, and thus limitation ineveryday ambulation is a serious clinical indicator thatneeds to be monitored by patients and their doctors.

Walking limitations are a hallmark of lumbar spinal ste-nosis (LSS). Anatomically, LSS is characterized by a nar-rowing of the lumbar spinal canal or nerve root foramen.Clinically, people with LSS present with a variety of symp-toms, including back pain, neurological deficits, and painin the lower limbs [5,6]. The cardinal symptom of LSS isneurogenic claudication, described as leg pain and/ornumbness, weakness, and tingling that is exacerbated bywalking, standing, and lumbar extension [7]. Such symp-toms of LSS often lead to substantial disability [8], wherethe activities requiring walking or prolonged standingare often avoided, and the health-related quality of life isdiminished [9–11].

The discussion of disability related to LSS benefits fromthe common conceptual framework provided by the Interna-tional Classification of Functioning, Disability and Health[12]. One of the fundamental principles of the classificationsystem is the difference between capacity (an individual’sability to perform a given task or an action in a controlledsetting) and performance (the activities performed by an in-dividual on a day-to-day basis in the context of their ownlife). The distinction between capacity and performance isessential to the study of the ambulatory disability causedby LSS.

Because walking limitations play such a central role inLSS, the adequate assessment of ambulation-related dis-ability is critical. The primary methods used to assesswalking can be grouped into three major categories:(1) questionnaires to assess patients’ perceived level ofwalking-related disability [13–18], (2) laboratory walkingtests to determine the ambulation capacity [19–23],and (3) community ambulation measured using activitymonitors to assess the walking performance in daily life[24–26]. Traditionally, walking has been assessed inLSS populations using self-report methods or objectivetests of walking capacity in the laboratory setting. How-ever, recent research has used activity monitors to mea-sure the daily physical activity of individuals froma variety of subject populations, including the elderly,stroke survivors, and cerebral palsy patients [18,27,28].The ability to measure the duration and intensity of activ-ity along with step counts has made activity monitors thegold standard in measuring the physical activity for thepurpose of medical research [24–26]. Yet this methodhas received little attention in the assessment of outcomesin LSS populations.

The purpose of the present study was to examine the re-lationships between walking capacity and walking perfor-mance in people with LSS by comparing the results ofself-report questionnaires, a walking capacity test, and ac-tivity monitoring of community ambulation. We hypothe-sized that self-reported walking disability would be morehighly correlated with performance than with capacity.

Materials and methods

Subjects

This was a prospective laboratory and clinical observa-tional study, which took place at a tertiary care spine clinic.Possible subjects were identified through a review of theclinic schedule for epidural injections at the University ofMichigan Spine Program. All patients scheduled for epidu-ral injection during a consecutive 3-month period, whowere identified as eligible for our study, were called onthe phone and provided information about our study.

Inclusion criteria were age older than 45 years and a clin-ical diagnosis of LSS by either a physiatrist or a surgeon.Diagnosis was based on the review of patient history, phys-ical examination, and confirmation of anatomical stenosison magnetic resonance imaging. All subjects were requiredto have documented symptoms of neurogenic claudication(eg, pain, numbness, weakness, or tingling in the lower

818 J. Conway et al. / The Spine Journal 11 (2011) 816–823

extremity brought on by lumbar extension, standing, orwalking). All subjects had been referred for epidural injec-tion to treat LSS. Stenosis may have been at single or mul-tiple levels. Exclusion criteria included disk herniation and/or other comorbidities that would limit walking capacity.Specific comorbidities warranting exclusion included anyother disorder that might be a limiting factor in ambulation.Examples include severe osteoarthritis of the hip or knee,peripheral vascular disease, coronary artery disease, andchronic obstructive pulmonary disease. Subjects agreeingto participate were scheduled for a meeting with researchstaff the week before their injection and guided throughthe informed consent process. This project was granted ap-proval by the institutional review board IRBMed at the Uni-versity of Michigan.

Data collection and measures

At the initial meeting, subjects filled out a questionnaire,completed a walking test, and were then given an activitymonitor and instructed to wear it for 7 days before their epi-dural injection.

Self-report measuresThe questionnaire included demographic information,

history of back/leg pain, walking specific questions, and fiveglobal function scales, including the Quebec Back PainDisability Scale [29], Pain Disability Index (PDI) [30], Os-westry Disability Index (ODI) [18], and the Physical Func-tion and Symptom Severity subscales of the Swiss SpinalStenosis Questionnaire (SSSQ) [31]. The walking specificquestions were as follows: ‘‘How would you say your walk-ing capacity is today, on a scale of 0 to 10, with 0 being yourworst day, and 10 being your best day?,’’ ‘‘I can walk — feetwithout a rest before I MUST stop,’’ and ‘‘When I am forcedto stop walking I stop because of pain in my legs.’’ Thesewalking questions are meant to provide additional walkinginformation, which is not provided by the SSSQ and havebeen shown to be reliable and valid, using the Self-PacedWalking Test as a criterion measure [32].

The Quebec Back Pain Disability Questionnaire wasused to assess pain and disability resulting from back pain.In the Quebec Back Pain Disability Questionnaire, patientsrate the degree of difficulty from zero (not at all difficult) tofive (unable to do) for performing 20 various activities,such as sleeping, standing for 20 to 30 minutes, and walk-ing several miles. A total score is calculated by summingall 20 responses, with a higher score representing greaterback pain–related disability. Test-retest reliability for theEnglish version is reported to be 0.93, and internal consis-tency for the scale is 0.95 [29].

The PDI consists of seven items used to measure a sub-ject’s perceived level of disability across various facets oflife, including self-care, social activity, and family respon-sibilities. Severity of disability for each domain is rated ona 0 to 10 visual analog scale, with a total maximum score of

70 points. A higher score represents higher pain-related dis-ability. Psychometric analysis of the PDI has supported itsconstruct validity and reliability [30].

The five-item Physical Function Scale of the SSSQ isused primarily to assess walking capacity. The scorewas calculated as the unweighted mean of the five itemsin the scale. The resulting possible scores of one to fourrepresent a range from mild to severe limitation in phys-ical function/walking [31]. The seven-item Symptom Se-verity Scale of the SSSQ was included to examineseverity of symptoms related to LSS and is scored asthe unweighted mean of the seven items in the scale, withscores from one to seven representing a range from mildto very severe pain. Both scales have been found to be in-ternally consistent, reliable, and responsive to clinicalchange [15,31–34].

The ODI is a nine-item questionnaire, which assessesdegree of back pain–related disability. Severity of pain anddisability in activities, such as walking, sitting, standing,and personal care, are rated on Likert scales of five or sixpoints. The ODI was calculated as a percentage of the totalpossible score of 53, with a greater score representing greaterback pain–related disability [9,35]. The ODI has repeatedlybeen shown to be a valid and reproducible measure of backpain–related disability and has been used specifically to eval-uate 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-36question 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 ComparativeHealth. Each scale score is calculated independently usingalgorithms defined by the developers [37].

Walking test and clinical measuresAfter completing the questionnaire, subjects completed

a Self-Paced Walking Test (SPWT) [34]. In the SPWT,walking capacity is measured as the distance a person isable to walk continuously on a flat surface at a self-selected pace until being forced to stop because of symp-toms of LSS, including neurogenic claudication (ie, pain,numbness, tingling, or weakness in at least one leg or but-tock) and/or low back pain, up to a limit of 30 minutes. Ifpatients reported stopping because of reasons other thanLSS symptoms (eg, general fatigue, shortness of breath,or dizziness), this was recorded, and the walking test datawere excluded from analysis. The SPWT was developedfor use as a criterion measure of walking capacity in LSSpatients and has been shown to have high retest reliabilityin this population [34]. Subjects completed the SPWTalonga flat hallway indoors or along the even surface of an out-door parking lot. Time was kept using a stopwatch, and dis-tance was measured via a distance wheel (Stanley DMW40;New Britain, CT, USA) directly following the path of thesubject. Immediately before and after the test, subjects

819J. Conway et al. / The Spine Journal 11 (2011) 816–823

completed 100-mm visual analog pain scales for their backand legs as well as a body diagram describing the type andlocation of symptoms (pain, tingling, numbness, and weak-ness) experienced at that time. During the SPWT, subjectswere asked to alert the research staff when symptoms ofLSS first began. The nature and location of these symptomswere recorded along with any other symptoms experiencedduring the test and the symptoms causing termination.

Activity monitorsOn completion of the walking tests, subjects were pro-

vided with an activity monitor (Actigraph GT1M; Acti-graph LLC, Pensacola, FL, USA) to wear for 7 days.Subjects were instructed to wear the activity monitors fromthe time they woke up in the morning to the time they wentto bed at night for 7 days before their epidural injection.Activity monitors were worn on an elastic band aroundthe waist at the level of the hip bone. Subjects were askedto remove the monitor only while showering or swimming.Subjects were also instructed how to complete a daily activ-ity log, which was used in the analysis to assess monitordata integrity. Activity monitors were collected by researchstaff at the time of the subject’s epidural injection. TheGT1M measures and records time varying accelerations30 times per second to produce ‘‘activity counts’’ and stepcounts for more than 60-second epochs. The activity scorethresholds are defined based on the algorithms developedby researchers, specifically for the Actigraph, and thecounts are determined based on the mathematical modelingprograms within the Actigraph software. Activity levelshave been classified as follows: Any score less than orequal to 100/min is sedentary, scores between 101/minand 1,952/min are light intensity, scores 1,953/min to5,724/min are moderate intensity, and more than 5,725/min is heavy intensity [38]. The Actigraph is widely ac-cepted in the field as a valid and reliable means of assessingambulatory physical activity [39–44].

Data analysisPearson product moment correlation coefficients were

used to examine the strength of relationships between vari-ables. In the case of nominal or ordinal variables, Spearmancorrelation coefficients were used. A p value of .05 wasused to determine the significance of correlation. An r valueof more than 0.80 was considered a very strong relation-ship; 0.60 to 0.79, a strong relationship; 0.40 to 0.59, a mod-erate relationship; and less than 0.40, a weak relationship[45,46].

For the activity monitor, a new variable was designed:maximum time of continuous activity. This was definedas the maximum number of continuous minutes perday at or above light intensity activity (activity scoreO100/min), with no more than 1 minute of activity belowlight intensity in between. The inclusion of bouts of activitywith single minutes of no activity between is to allow forthe normal stop-and-go nature of activity in one’s life. This

was decided on, because in our other work with LSS pa-tients, in response to a question addressing the amount oftime needed to recover after being forced to stop walkingbecause of pain, the minimum time recorded was 2 min-utes. Therefore, we determined that allowing for a minuteof relative inactivity was acceptable and reflective of thefunctional demands of community activity.

Results

Each of the 12 recruited subjects completed all the threephases of testing, including the self-report measures,SPWT, and activity monitor. Subject noncompliance,scheduling difficulties, and one case of an activity monitorthat lost power prevented us from collecting the full 7 daysof activity data on seven (58%) subjects. The minimumnumber of days of collected data was 4 days, with an aver-age of 6.360.9 days per subject. All subjects reported ter-minating the SPWT because of symptoms of LSS(neurogenic claudication and/or low back pain); none werelimited by other diseases.

Basic demographic and descriptive data for the subjectpopulation can be seen in Table 1. Of the total sample,75% were male, and the mean age was 66.369.8 years. Itshould be noted that all but one of the subjects had a bodymass index (BMI) in the overweight or obese range, with anaverage BMI of 33.467.8. Most subjects (83%) had eitherback pain or leg pain with rest, and 100% of subjects hadboth back pain and leg pain with walking. These symptomsare in keeping with the clinical diagnosis of LSS. Scores forthe ODI and Physical Function Scale of the SSSQ are sim-ilar to those found in the previous studies of walking inLSS [15,32,34].

The results from both the SPWT and the activity monitordata can be seen in Table 2. Our data exhibit a wide rangeof both capacity and performance among our subject popu-lation. This reflects the variable nature of the impact of LSSon each individual. Table 3 illustrates correlations betweenthe SPWT, activity monitor data, and self-report measures.A strong relationship (r50.63, p!.05) was observed be-tween the distance on the SPWT and maximum time ofcontinuous activity per day, as measured by the activitymonitor (r50.63). A moderate relationship was observedbetween the SPWT and overall activity per day (r50.53),but this was not statistically significant (p5.078).

Fifteen self-report measures were found to have statisti-cally significant correlations with the SPWT, activity mon-itor (maximum time of continuous activity), or both. Ofthese 15 measures, 13 (87%) were more highly correlatedto the SPWT than the activity monitor. The SPWT hada strong relationship (rO0.60, p!.05) with the QuebecBack Pain Disability Scale, Swiss Spinal Stenosis PhysicalFunction Survey, and ODI, as well as the SF-36 PhysicalFunctioning Scale, estimates of maximum distance withoutstopping, and weakness in the legs and feet.

Table 1

Subject demographics, clinical presentation, and self-report measures (n512)

Subject factor All subjects (n512) Standard deviation Minimum Maximum

Age (y) 66.25 9.8 53 81

Gender (% male) 75.0

Body mass index 33.4 7.8 18.8 47.1

Duration of symptoms (y) 4.7 1.5 1 10.8

Back pain at rest 10 (83.3%) —

Back pain with walking 12 (100%) —

Leg pain at rest 10 (83.3%) —

Leg pain with 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 Lifey 3.2 0.84 1 5

Overall Healthy 3.3 1.1 2 5

Life Satisfactiony 3.2 0.83 2 5

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; SF-36, 36-Item Short Form Health Survey.

* Score of most painful leg was used.y From SF-36.

820 J. Conway et al. / The Spine Journal 11 (2011) 816–823

The activity monitor data were significantly correlatedwith only two outcome measures. Walking limited by painin the legs exhibited a strong relationship to both averageactivity per day (r50.623, p!.05) and maximum continu-ous activity per day (r50.754, p!.01). Both average activ-ity per day and maximum continuous activity per day hada very strong relationship (r50.885 and r50.885, respec-tively, p!.01) with Question #12 on the Quebec Back PainDisability Questionnaire, in which subjects were asked torate the difficult of running two blocks.

Discussion

This was the first study of its kind to examine the rela-tionship between walking capacity and walking perfor-mance in people with LSS. A strong relationship wasdemonstrated between laboratory-based walking capacityand maximum daily continuous activity measured with anactivity monitor. A moderate, yet nonsignificant relation-ship was observed between walking capacity and averagedaily community ambulation. Questionnaires commonly

used to evaluate walking in patients with LSS were shownto be mostly associated with capacity, not performance.This research also developed the activity monitor parameterof maximum continuous daily activity, which proved to bemore highly correlated with walking capacity than anyother measure of community-based activity.

The strengths of this study include the use of multiplewell-validated questionnaires to assess self-reported walk-ing disability. The reliability of collected data was strength-ened via use of the SPWT and extended period of time(7 days) in which the subjects were instructed to wearthe activity monitor. Limitations of this study includesample size, incomplete follow-up data, and noncompli-ance. A lack of variation in gender and BMI among ourstudy population may provide a degree of sampling error.Diagnostic criteria for stenosis, and thus inclusion criteriafor this study, can be debated. The relationship betweenradiological stenosis and clinical symptoms has been seri-ously challenged by a number of studies [47]. A recentstudy has shown an important disagreement between expertsurgeons as to the presence of neurogenic claudicationamong persons who have been offered surgery for spinal

Table 2

Physical tests of capacity and performance (n512)

Test Mean Standard deviation Minimum Maximum

SPWT distance (m) 775.8 725.6 60 2,065

SPWT time (s) 840.4 690.2 67 1,800

SPWT distance to first sx (m) 202.5 296.1 10 900

Activity count/d (Actigraph activity count) 99958.9 69224.7 21,906 246,249

Maximum time of continuous activity (s) 1590 768 450 2768.4

Steps/d 2821.9 1996.8 790 6,919

Meters walked/d 1687.7 1447.0 371.3 4912.5

SPWT, Self-Paced Walking Test; SPWT distance to first sx, distance to the first onset of symptoms reported by the subject during the SPWT.

821J. Conway et al. / The Spine Journal 11 (2011) 816–823

stenosis [48]. However, in keeping with current convention,a clinical diagnosis of LSS, including the presence of neu-rogenic claudication, with anatomical stenosis confirmedon magnetic resonance imaging, was used. Likely, the pop-ulation represented persons whom other reasonable clini-cians would believe to have spinal stenosis.

Participants in this study had lower average daily stepcounts than the previous studies of older adults [25,49].Compared with research by Cavanaugh et al. [25], subjectsin the present study had a markedly lower average daily stepcount (2821.9 steps/d) than both healthy older adults(9981.7 steps/d) and older adults with ‘‘functional limita-tions’’ (7681.5 steps/d). This finding is a reminder of the

Table 3

Relationships between questionnaires, capacity (as measured by the SPWT), and

Item

Walking capacity (SPWT)

SPWT distance

SPWT distanc

to first sympto

SPWT distance 1 0.563

SPWT time to first symptoms 0.563 1

Activity count/d 0.527 �0.075

Maximum time of continuous activity 0.629* 0.344

Quebec �0.638* �0.549

Oswestry �0.595* �0.310

Swiss.PF �0.610* �0.427

SF-36 PF 0.825** 0.325

Walking capacity 0.682* 0.422

Estimated walking 0.886** 0.659*

Leg pain 0.492 0.216

Quebec_Stand �0.551 �0.681*

Quebec_Walk �0.755** �0.439

Quebec_Reach �0.650* �0.436

Quebec_Run �0.664* �0.151

Quebec_Groceries �0.727* �0.628

Swiss.PF_Walk �0.715* �0.622*

Swiss.SS_Weak �0.742** �0.463

Swiss.SS_Balance �0.673* �0.646*

SPWT, Self-Paced Walking Test; Quebec, Quebec Back Pain Disability Scale

naire; Swiss.SS, Symptom Severity Scale of the Swiss Spinal Stenosis Questionn

Health Survey Physical Functioning; Walking capacity, response to this question:

with 0 being your worst day, and 10 being your best day?’’; Estimated walking, r

stop’’; Leg pain, response to this question: ‘‘When I am forced to stop walking I s

ing up for 20 to 30 minutes; Quebec_Walk, difficulty in walking several miles; Qu

difficulty rating for running two blocks; Quebec_Groceries, difficulty rating for

Swiss.SS_6, rating for severity of leg and foot weakness; Swiss.SS_7, rating for

* p!.05.

** p!.01.

severe compromise in life function imposed by clinical spi-nal stenosis.

This study provided new insight into the relationship be-tween capacity and performance in LSS. Recent researchby Zalewski et al. [49] found that in residents of a criticalcare retirement community there was no relationship be-tween performance on a clinic-based test of walking capac-ity and community-based walking performance. The resultsof the present study, however, did demonstrate a significantassociation between walking capacity and walking perfor-mance; capacity to walk in the laboratory was observedto be significantly correlated with the average daily boutof maximum continuous activity in the community.

performance (as measured by the activity monitor) in LSS populations

Walking performance (activity monitor)

Stronger

correlation

e

ms Activity count/d

Maximum time

of continuous activity

0.527 0.629* —

�0.075 0.344 —

1 0.879** —

0.879** 1 —

�0.065 �0.162 Capacity

�0.148 �0.070 Capacity

0.015 �0.107 Capacity

0.521 0.500 Capacity

0.304 0.265 Capacity

0.470 0.541 Capacity

0.623* 0.754** Performance

�0.069 �0.269 Capacity

�0.175 �0.274 Capacity

�0.291 �0.282 Capacity

�0.884** �0.825** Performance

�0.192 �0.375 Capacity

�0.249 �0.375 Capacity

0.127 �0.081 Capacity

0.057 �0.072 Capacity

; Swiss.PF, Physical Function Scale of the Swiss Spinal Stenosis Question-

aire; Oswestry, Oswestry Disability Index; SF-36 PF, 36-Item Short Form

‘‘How would you say your walking capacity is today, on a scale of 0 to 10,

esponse to this question: ‘‘I can walk — feet without a rest before I MUST

top because of pain in my legs’’; Quebec_Stand, difficulty rating for stand-

ebec_Reach, difficulty rating for reaching up to high shelves; Quebec_Run,

carrying two bags of groceries; Swiss.PF_1, rating for walking distance;

severity of balance problems.

822 J. Conway et al. / The Spine Journal 11 (2011) 816–823

Although our results showed a correlation betweenwalking capacity and walking performance in patients withLSS, our findings also suggest that walking capacity andwalking performance are not the same and as such shouldbe treated as two separate entities. Maximum time of dailycontinuous activity appeared to be a representative of walk-ing capacity, but the more global measure of walking per-formance (average daily activity) was not significantlyrelated to laboratory-based walking capacity. This differ-ence between capacity and performance appears to be of vi-tal importance to the interpretation of questionnairescommonly used to assess the disability level of people withLSS. Our data show that self-report measures used in thisstudy are an indicator of capacity, not performance. There-fore, the data elicited by these questionnaires give an in-complete, and possibly misleading, picture of a patient’slevel of disability.

This apparent discrepancy between walking capacityand walking performance has implications for both clinicalpractice and research related to treatment and assessment ofmobility in LSS. The functional goal of interventions forLSS is thought to be the improvement in performance,not capacity. A person who is made more capable of walk-ing but does not take advantage of that capacity via in-creased performance will neither have an improvement inthe quality of life nor reap the well-documented benefitsof walking participation on overall health.

Spinal stenosis is defined as an anatomical and a physio-logical disorder. However, its impact on people’s lives ismul-tidimensional. As such, a single mode of treatment for LSScannot be assumed to improve all facets of the disease. Treat-ments for LSS are commonly based on capacity; a treatmentis deemed successful if the patient’s ability to walk is im-proved. But if, as mentioned, this improvement in capacityis notmetwith an improvement in performance (ie, the actualwalking done by the patient) then the patient’s participationin daily activities and the quality of life has gone unchanged.Thus, the treatment of patients performing under their capac-ity level will not result in a significant increase in daily activ-ity levels unless the limiting factors to performance, whetherthey be physical, social, or psychological, are identified andsubsequently addressed. A multidisciplinary assessment andperhaps multidisciplinary treatment of spinal stenosis pa-tients may result in better outcomes.

In terms of research and outcomes assessment, this studyshows that even a single function such as ambulation hasmany dimensions that cannot be measured using a singletest or survey. If we are using outcome tools focusing oncapacity (such as the SPWT or self-report tools), we maybe missing the important impact or lack of impact on pa-tients’ day-to-day lives (performance). Activity monitorsas used in the present study should be considered in futureresearch with LSS patients, especially when trying to definethe effects of interventions. Research into the nature of par-ticipation deficits and factors (such as high BMI) that maylead to such deficits may result in interventions that are

more specific to the actual problem of the patient. A largerdatabase of ambulation profiles of persons with spinal ste-nosis will help us understand how capacity limitations af-fect participation and how people adapt to those limitations.

Finally, these data suggest that activity monitors may be-come useful in measurement of function in the clinical set-ting. It is possible that, in the future, the criteria for surgicalintervention for spinal stenosis would include a drop inweekly activity below a certain level or a slope of declinethat suggests that surgery is the better choice. A poor rela-tionship between capacity and participation may alert theclinician that a multidisciplinary approach is needed.

Conclusion

There is a relationship between capacity to walk and ac-tual performance in walking in the community, but it is notexact. Questions about ambulation on most standardizedoutcome tools appear to relate best to capacity; yet perfor-mance and participation are the more important life goals.This difference highlights the need for researchers to usetools such as activity monitors to measure participation asan ultimate outcome measure and for clinicians to focuson the multifaceted barriers that exist between improvedcapacity and improved performance in daily life.

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