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Changes in Objectively Measured Physical Activity (Performance) After Epidural Steroid Injection for Lumbar Spinal Stenosis

      Abstract

      Tomkins-Lane CC, Conway J, Hepler C, Haig AJ. Changes in objectively measured physical activity (performance) after epidural steroid injection for lumbar spinal stenosis.

      Objective

      To examine changes in objectively measured physical activity (performance) at 1 week following epidural steroid injection for lumbar spinal stenosis.

      Design

      Prospective cohort.

      Setting

      University spine program.

      Participants

      Individuals (N=17) who were undergoing fluoroscopically guided epidural steroid injection for symptomatic lumbar spinal stenosis (mean age ± SD, 70.1±6.7; 47% women).

      Intervention

      Fluoroscopically guided epidural injection.

      Main Outcome Measure(s)

      The 2 primary outcomes, measured with accelerometers, were total activity (performance) measured over 7 days and maximum continuous activity (capacity). Walking capacity was also assessed with the Self-Paced Walking Test, and subjects completed the Oswestry Disability Index, Swiss Spinal Stenosis Questionnaire, Medical Outcomes Study 36-Item Short-Form Health Survey, visual analog pain scales, and body diagrams.

      Results

      At 1 week postinjection, 58.8% of the subjects demonstrated increased total activity and 53% had increased maximum continuous activity, although neither change was statistically significant. Significant improvements were observed in a number of the self-report instruments, including the Physical Function Scale of the Swiss Spinal Stenosis Questionnaire, general health (Medical Outcomes Study 36-Item Short-Form Health Survey), role-limitation emotional (Medical Outcomes Study 36-Item Short-Form Health Survey), leg pain intensity (visual analog pain scales), and presence of leg weakness.

      Conclusions

      While patients perceived improvements in pain and function following injection, these improvements were not reflected in significant changes in performance or capacity. Future studies will continue to find value in subjective measures of pain and quality of life. However, with modern technology, performance is no longer a subjective variable. Use of activity monitors to objectively measure performance can result in more rigorous validation of treatment effects, while simultaneously highlighting the potential need for additional postinjection rehabilitation aimed at improving performance.

      Key Words

      List of Abbreviations:

      BMI (body mass index), ESI (epidural steroid injection), LSS (lumbar spinal stenosis), MCID (minimal clinically important difference), ODI (Oswestry Disability Index), SF-36 (Medical Outcomes Study 36-Item Short-Form Health Survey), SPWT (Self-Paced Walking Test)
      PRIMARY GOALS when treating symptomatic lumbar spinal stenosis (LSS) include symptom reduction and restoration of walking function. Epidural steroid injections (ESIs) are commonly used for these purposes in people with LSS.
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      Epidural steroid injections for lumbar spinal stenosis.
      It is thought that ESIs may help reduce pain and improve standing and walking tolerance.
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      Fluoroscopically guided caudal epidural steroid injections in degenerative lumbar spine stenosis.
      Treatment of LSS using various ESI techniques (transforaminal, caudal, interlaminar, fluoroscopically guided, and non–fluoroscopically guided) has been described.
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      A retrospective analysis of the efficacy of epidural steroid injections.
      Yet there have been a limited number of studies evaluating the efficacy of ESI for LSS. Studies evaluating non–fluoroscopically guided ESI for LSS all showed short-term benefit ranging from 1 week to 2 months of relief.
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      Symptoms of spinal stenosis do not improve after epidural steroid injection.
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      The use of epidural steroids in the treatment of lumbar radicular pain: a prospective, randomized, double-blind study.
      More recent studies that used fluoroscopic guidance demonstrate variable results, with all showing some short-term benefit (1wk–2mo).
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      Treatment of lumbar spinal stenosis with epidural steroid injections: a retrospective outcome study.
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      Effectiveness of transforaminal epidural steroid injections in patients with degenerative lumbar scoliotic stenosis and radiculopathy.
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      Effectiveness of transforaminal epidural steroid injections in low back pain: a one-year experience.
      Although most studies of ESI for LSS have demonstrated consistent short-term improvement in subjective symptoms and perceived function,
      • Delport E.G.
      • Cucuzzella A.R.
      • Marley J.K.
      • et al.
      Treatment of lumbar spinal stenosis with epidural steroid injections: a retrospective outcome study.
      • Kapural L.
      • Mekhail N.
      • Bena J.
      • et al.
      Value of the magnetic resonance imaging in patients with painful lumbar spinal stenosis (LSS) undergoing lumbar epidural steroid injections.
      • Rosen C.D.
      • Kahanovitz N.
      • Bernstein R.
      • Viola K.
      A retrospective analysis of the efficacy of epidural steroid injections.
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      Epidural steroid injection for nerve root compression: a randomised, controlled trial.
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      it has been suggested that more rigorous measurement of function is warranted.
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      Epidural steroid injections in the treatment of lumbar spinal stenosis: efficacy and predictability of successful response.
      Recent research with the LSS population suggests that when measuring physical function, we need to recognize and assess the 2 distinct components: capacity and performance.
      • Conway J.
      • Tomkins C.C.
      • Haig A.J.
      Walking assessment in people with lumbar spinal stenosis: capacity, performance, and self-report measures.
      Defined by the International Classification of Functioning, Disability and Health capacity is the ability to perform a given task in a controlled environment, while performance reflects physical activity in the context of a person's real life.
      World Health Organization
      International classification of functioning, disability and health: ICF.
      It appears that the majority of traditional outcomes used with LSS populations (questionnaires, walking tests) are assessing the construct of capacity, not performance.
      • Conway J.
      • Tomkins C.C.
      • Haig A.J.
      Walking assessment in people with lumbar spinal stenosis: capacity, performance, and self-report measures.
      It is thought that the goal of intervention is to improve performance—actual physical activity and function in daily life. Therefore, performance is a critical outcome for the LSS population.
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      • Carragee E.J.
      Commentary: one small step.
      Performance is important in identifying barriers to function and the impact of spinal pathology on real life.
      Only recently, using activity monitors (accelerometers) have we been able to objectively measure performance. To our knowledge, the effect of ESI on performance has yet to be examined in an LSS population. Therefore, the objective of this study was to examine changes in objectively measured physical activity (performance) in people undergoing ESI for symptomatic LSS.

      Methods

      Subjects

      Possible participants were identified through review of the clinic schedule for the University of Michigan Spine Program. Participants were identified if they were scheduled for fluoroscopically guided ESI for symptomatic LSS by physicians certified in both physical medicine and rehabilitation, and pain medicine. To be included, participants were required to have documented LSS diagnosed by a physiatrist or a surgeon who had examined both the patient and the lumbar magnetic resonance imaging. A clinical presentation of LSS (reported neurogenic claudication) was also required for inclusion. After being identified, subjects were contacted by phone. This method was chosen given the rapid time frame between scheduling and actual injection. Potential participants were asked whether they were interested in hearing about the study. If interested, they were provided with information. Subjects agreeing to participate were scheduled for a meeting with research staff the week prior to their injection to review inclusion and exclusion criteria, as well as the informed consent documents. Exclusion criteria included disk herniation or any disorder other than spinal stenosis that in the opinion of the investigators could put the subject at risk during testing or act as the rate-limiting factor in ambulation (balance disorders, chronic obstructive pulmonary disorder, asthma, neuromuscular disease, severe lower limb arthritis, polyneuropathy, peripheral vascular disease). This project was granted approval by the Institutional Review Board at the University of Michigan.

      Data Collection and Measures

      One week prior to injection, participants completed a questionnaire and the Self-Paced Walking Test (SPWT). Subjects were provided with an activity monitor (Actigrapha GT1M) and instructed to wear it for the 7 days prior to their injection.

      Self-report measures

      The baseline questionnaire included demographic information, 10-cm visual analog pain scales for the back and legs, and a body diagram for indicating the location of pain, numbness, tingling, and weakness. A minimal clinically important difference (MCID) of 1.6cm for leg pain and 1.2cm for back pain has been suggested by Copay et al
      • Copay A.G.
      • Glassman S.D.
      • Subach B.R.
      • et al.
      Minimum clinically important difference in lumbar spine surgery patients: a choice of methods using the Oswestry Disability Index, Medical Outcomes Study questionnaire Short Form 36, and pain scales.
      on the basis of the evaluation of lumbar spine patients (28.5% had LSS), while Parker et al
      • Parker S.L.
      • Mendenhall S.K.
      • Shau D.N.
      • et al.
      Minimum clinically important difference in pain, disability, and quality of life after neural decompression and fusion for same-level recurrent lumbar stenosis: understanding clinical versus statistical significance.
      suggest an MCID of 5.0cm for leg pain and 2.2cm for back pain on the basis of a study of patients with LSS. Standardized instruments included in the questionnaire were the Oswestry Disability Index (ODI), the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36), and the Symptom Severity and Physical Function Scales of the Swiss Spinal Stenosis Questionnaire.
      The ODI is a 9-item questionnaire designed to provide information regarding how back and/or leg pain affects a person's ability to function in daily life.
      • Fairbank J.C.
      • Couper J.
      • Davies J.B.
      • et al.
      The Oswestry low back pain disability questionnaire.
      Severity of pain and disability in activities such as walking, standing, personal care, and travel are rated on a 5- or a 6-point scale. This instrument is psychometrically sound and is recommended as a standard measurement to assess back pain–related function.
      • Fairbank J.
      Use of Oswestry Disability Index (ODI).
      • Fairbank J.C.
      The use of revised Oswestry Disability Questionnaire.
      • Fairbank J.C.
      • Pynsent P.B.
      The Oswestry Disability Index.
      • Pratt R.K.
      • Fairbank J.C.
      • Virr A.
      The reliability of the Shuttle Walking Test, the Swiss Spinal Stenosis Questionnaire, the Oxford Spinal Stenosis Score, and the Oswestry Disability Index in the assessment of patients with lumbar spinal stenosis.
      It has been validated specifically for the LSS population.
      • Tomkins-Lane C.C.
      • Battie M.C.
      Validity and reproducibility of self-report measures of walking capacity in lumbar spinal stenosis.
      Published values for MCID on the ODI in LSS populations include 8.2,
      • Parker S.L.
      • Mendenhall S.K.
      • Shau D.N.
      • et al.
      Minimum clinically important difference in pain, disability, and quality of life after neural decompression and fusion for same-level recurrent lumbar stenosis: understanding clinical versus statistical significance.
      11,
      • Lauridsen H.H.
      • Hartvigsen J.
      • Manniche C.
      • et al.
      Responsiveness and minimal clinically important difference for pain and disability instruments in low back pain patients.
      and 12.8.
      • Copay A.G.
      • Glassman S.D.
      • Subach B.R.
      • et al.
      Minimum clinically important difference in lumbar spine surgery patients: a choice of methods using the Oswestry Disability Index, Medical Outcomes Study questionnaire Short Form 36, and pain scales.
      The 5-item Physical Function Scale of the Swiss Spinal Stenosis Questionnaire is primarily used to assess walking capacity. Limitations are rated on a 1 to 4 scale, with a lower score indicating better physical function. The 7-item Symptom Severity Scale was included to examine the severity of symptoms related to LSS. Both the Physical Function Scale and the Symptom Severity Scale have previously been demonstrated to be internally consistent, reliable, and responsive to clinical change in the LSS population.
      • Tomkins-Lane C.C.
      • Battie M.C.
      Validity and reproducibility of self-report measures of walking capacity in lumbar spinal stenosis.
      • Stucki G.
      • Liang M.H.
      • Fossel A.H.
      • et al.
      Relative responsiveness of condition-specific and generic health status measures in degenerative lumbar spinal stenosis.
      • Stucki G.
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      • Liang M.H.
      • et al.
      Measurement properties of a self-administered outcome measure in lumbar spinal stenosis.
      • Walsh T.L.
      • Hanscom B.
      • Lurie J.D.
      • et al.
      Is a condition-specific instrument for patients with low back pain/leg symptoms really necessary? The responsiveness of the Oswestry Disability Index, MODEMS, and the SF-36.
      • Tomkins C.C.
      • Battie M.C.
      • Hu R.
      Construct validity of the physical function scale of the Swiss Spinal Stenosis Questionnaire for the measurement of walking capacity.
      The published MCID for both scales is 0.5.
      • Stucki G.
      • Daltroy L.
      • Liang M.H.
      • et al.
      Measurement properties of a self-administered outcome measure in lumbar spinal stenosis.
      The SF-36 is a multidimensional generic health status instrument that consists of 8 health concept scales (physical functioning, role limitation-physical, bodily pain, general health, vitality, social function, role limitation-emotional, and mental health). Each scale score is calculated independently. For each scale, item scores are summed and transformed into a scale ranging from 0 (indicating worse health state) to 100 (indicating best health state). In total, the instrument contains 36 items that represent a broad array of health concepts.
      • Ware Jr, J.E.
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      The MOS 36-item short-form health survey (SF-36), I: conceptual framework and item selection.
      The psychometric properties of the SF-36 have been well established.
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      The MOS 36-Item Short-Form Health Survey (SF-36), II: psychometric and clinical tests of validity in measuring physical and mental health constructs.
      An MCID of 3 for the SF-36 subscales has been suggested for back pain populations by Lauridsen et al.
      • Lauridsen H.H.
      • Hartvigsen J.
      • Manniche C.
      • et al.
      Responsiveness and minimal clinically important difference for pain and disability instruments in low back pain patients.
      Although not specific to LSS, Samsa et al
      • Samsa G.
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      Determining clinically important differences in health status measures: a general approach with illustration to the Health Utilities Index Mark II.
      similarly suggest a range of 3 to 5 as a minimal clinically important change for all scales in the general population.

      Walking test and clinical measures

      After completing the questionnaire, subjects completed an SPWT.
      • Tomkins C.C.
      • Battie M.C.
      • Rogers T.
      • et al.
      A criterion measure of walking capacity in lumbar spinal stenosis and its comparison with a treadmill protocol.
      In the SPWT, walking capacity is measured as the distance a person is able to walk on a flat surface at a self-selected pace until being forced to stop because of symptoms of LSS (or other reasons). The SPWT was developed for use as a criterion measure of walking capacity in patients with LSS and has been shown to have high retest reliability in this population.
      • Tomkins C.C.
      • Battie M.C.
      • Rogers T.
      • et al.
      A criterion measure of walking capacity in lumbar spinal stenosis and its comparison with a treadmill protocol.
      Subjects completed the SPWT along a flat hallway indoors or along the even surface of an outdoor parking lot. Subjects walked continuously until they felt that they needed to stop or until the maximum time of 30 minutes was reached. Time was kept by stopwatch, and distance was measured via a distance wheel directly following the path of the subject.

      Activity monitors

      Upon completion of the walking tests, subjects were provided with an activity monitor (Actigraph GT1M) 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 the 7 days prior to their epidural injection. Activity monitors were worn on an elastic band around the waist at the level of the hip on the same side (left or right) for all testing days. Subjects were instructed to remove the monitor only when in contact with water (bathing, swimming). The monitors were collected by staff at the time of the subject's epidural injection.
      Activity monitors (accelerometers) are small devices usually worn on the hip or lower back
      • Trost S.G.
      • McIver K.L.
      • Pate R.R.
      Conducting accelerometer-based activity assessments in field-based research.
      that measure movement in terms of acceleration.
      • Chen K.Y.
      • Bassett Jr, D.R.
      The technology of accelerometry-based activity monitors: current and future.
      Acceleration is recorded as a voltage signal, and these voltage outputs are known as “counts.” Counts can be used to estimate volume, duration, and intensity of physical activity. A large body of literature supports the validity and reliability of accelerometers for the measurement of physical activity in older adults.
      • Sumukadas D.
      • Laidlaw S.
      • Witham M.D.
      Using the RT3 accelerometer to measure everyday activity in functionally impaired older people.
      • Rikli R.E.
      Reliability, validity, and methodological issues in assessing physical activity in older adults.
      • Fehling P.C.
      • Smith D.L.
      • Warner S.E.
      • et al.
      Comparison of accelerometers with oxygen consumption in older adults during exercise.
      • Kochersberger G.
      • McConnell E.
      • Kuchibhatla M.N.
      • et al.
      The reliability, validity, and stability of a measure of physical activity in the elderly.
      • Culhane K.M.
      • O'Connor M.
      • Lyons D.
      • et al.
      Accelerometers in rehabilitation medicine for older adults.
      There is a general consensus that accelerometers provide a valid indicator of overall physical activity.
      • Welk G.J.
      Use of accelerometry-based activity monitors to assess physical activity.

      Follow-up

      One week following injection, all participants were asked to return to repeat testing, including the questionnaires, walking test, and 7-day activity monitoring. All questionnaires were completed at this time. The activity monitoring took place between days 7 and 14 postinjection. Follow-up after 1 week was chosen because the pain-relieving effect of steroid injections is believed to begin to be significant at 1 week. For example, Ridley et al
      • Ridley M.G.
      • Kingsley G.H.
      • Gibson T.
      • et al.
      Outpatient lumbar epidural corticosteroid injection in the management of sciatica.
      first found a statistically significant improvement in rest and walking pain at 1 and 2 weeks after injection, and this improvement was maintained up to 12 weeks.
      • Ridley M.G.
      • Kingsley G.H.
      • Gibson T.
      • et al.
      Outpatient lumbar epidural corticosteroid injection in the management of sciatica.

      Data Analysis

      Performance variables were extracted from the accelerometer data using a program designed in MATLABb for this purpose. Volume of activity was calculated as the total activity count over 7 days (counts/wk) and maximum intensity as the maximum number of counts per minute during the 7 days. The total duration of activity at each of the following intensity thresholds was calculated: sedentary (<100 counts/min), light (101–1952 counts/min), moderate (1953–5724), and high (>5725). These are standard cutoff points that have been validated by Freedson et al
      • Freedson P.S.
      • Melanson E.
      • Sirard J.
      Calibration of the Computer Science and Applications, Inc. accelerometer.
      using direct comparison with energy expenditure (oxygen consumption per unit time). Capacity was measured as maximum continuous activity. This variable was determined as the maximum number of consecutive minutes above sedentary (>100) with no more than 1 minute of counts <100 between (to allow for realistic stop and start activity). We also calculated maximum continuous activity with no breaks allowed (number of consecutive minutes >100 counts/min).
      The goal sample size was 15. This sample size was based on data from an unpublished study of patients with LSS showing a mean of 4218±800 steps per day. Using 4218±800 as a baseline, with a sample size of 15, provided 80% power to detect a 20% increase from pre- to postinjection. We also conducted a post hoc analysis to determine the sample size required to detect a minimal clinically important change of .50 on the Physical Function Scale and the Symptom Severity Scale, powered at .80. The sample size estimate was 16. Therefore, with 17 subjects, the study was adequately powered to detect changes in both performance and self-report measures.
      Descriptive statistics were used to describe the study sample. One-way repeated-measures analysis of variance was used to compare pre- and postintervention measurements. A post hoc Bonferroni correction was applied to adjust for multiple comparisons and reduce the risk of type 1 error. Chi-square tests were used for categorical variables. Post hoc correlation analysis examined the relation between demographic variables and change in performance and self-report variables. The P value was defined as .05 for all analyses. SPSS Version 17c was used for all analyses.

      Results

      The sample comprised 17 participants who had fluoroscopically guided epidural injection for symptomatic LSS. Their average age was 70.1±6.7 years, and 47% were women (table 1). Follow-up occurred at an average of 6.7±1.0 days following injection (range 6–10d). No subjects had any therapy between injection and follow-up. The average number of days of activity monitoring preinjection was 6.47±1.1 (range 4–7d) and 5.8±1.7 (range 4–7d) postinjection. All subjects met the minimum requirement of 4 days of activity monitor wear both pre- and postinjection. Post hoc analysis was conducted to ensure that there were no differences for any results between those who wore the monitor for the full 7 days and those who wore the monitor for fewer than 7 days at either baseline or follow-up. There were no significant relations between demographic variables (age, sex, height, weight, or body mass index [BMI]) and change in performance or self-reported outcomes.
      Table 1Participant Characteristics
      VariableMale Participants (n=9)Female Participants (n=8)All Participants (N=17)
      Age (y)68.3±7.273.4±4.870.1±6.7
      Height (m)1.73±0.081.59±0.661.68±0.1
      Weight (kg)81.7±25.686.1±29.883.5±26.4
      BMI (kg/m2)26.9±7.633.5±9.829.5±8.9
      BMI categories:
       Number in normal BMI range (20–25)415
       Number in overweight BMI range (25–29)235
       Number with obese BMI (≥30)347
      NOTE. Values are mean ± SD or as otherwise indicated.
      Results of the pre- and postinjection testing can be found in Table 2, Table 3. Accelerometer variables included total activity, peak activity, steps per day, percentage of time spent in the various activity ranges, and maximum continuous activity. Ten subjects (58.8%) demonstrated increased total activity postinjection, and 100% had increased average daily activity. Thirty-five percent demonstrated increased peak activity, 59% had increased steps per day, 53% decreased time spent in the sedentary range, and 53% showed increased maximum continuous activity (both with and without breaks included). Although the mean values for all the activity monitor outcomes improved from baseline to postinjection, none of the changes were statistically significant.
      Table 2Activity Monitor Results (N=17)
      VariablePreinjectionPostinjection
      Total activity (activity counts)561,315±455,904711,730±502,688
      Peak activity (activity counts)3,458±1,2634,781±6,552
      Average daily steps2,544±1,9252,846±2,137
      Percentage of total counts in sedentary range (%)89.5±6.088.6±5.8
      Percentage of total counts in light range (%)10.3±5.711.1±5.6
      Percentage of total counts in moderate range (%)0.02±.040.36±0.50
      Percentage of total counts in high range (%)0.00±0.000.02±0.09
      Maximum minutes of continuous activity (>light) with 1-min breaks allowed (min)49.5±39.959.9±69.6
      Maximum minutes of continuous activity (>light) with no breaks allowed (min)31.6±34.648.6±71.5
      NOTE. Values are mean ± SD.
      Table 3Traditional Clinical Outcomes Results (N=17)
      VariablePreinjectionPostinjection
      ODI (%)49.1±10.951.4±8.3
      Physical Function Scale2.6±0.402.3±0.51
      Different from baseline at adjusted P level indicated in parentheses. All values with no P value indicated were not significantly different between pre- and postinjection at P< .05.
       (P=.007)
      Symptom Severity Scale2.7±0.542.6±0.47
      SF-36 general health47.5±17.455.2±19.7
      Different from baseline at adjusted P level indicated in parentheses. All values with no P value indicated were not significantly different between pre- and postinjection at P< .05.
       (P=.008)
      SF-36 physical functioning27.1±18.027.7±16.3
      SF-36 role physical15.4±32.511.8±28.1
      SF-36 bodily pain39.3±11.544.5±18.3
      SF-36 vitality55.0±15.457.6±17.7
      SF-36 social functioning55.9±13.660.3±17.1
      SF-36 role emotional47.1±41.872.5±12.9
      Different from baseline at adjusted P level indicated in parentheses. All values with no P value indicated were not significantly different between pre- and postinjection at P< .05.
       (P=.04)
      SF-36 mental health66.4±14.158.1±18.4
      VAS pain back (100-mm scale)41.5±29.833.8±26.1
      VAS pain legs (100-mm scale)52.0±31.942.8±33.3
      Different from baseline at adjusted P level indicated in parentheses. All values with no P value indicated were not significantly different between pre- and postinjection at P< .05.
       (P=.05)
      Legs feel weak (% yes)53.414.3
      Different from baseline at adjusted P level indicated in parentheses. All values with no P value indicated were not significantly different between pre- and postinjection at P< .05.
      (P=.008)
      SPWT (m)772.3±728.7907.6±685.8
      Abbreviation: VAS, visual analog pain scales.
      NOTE. Values are mean ± SD unless otherwise indicated.
      low asterisk Different from baseline at adjusted P level indicated in parentheses. All values with no P value indicated were not significantly different between pre- and postinjection at P< .05.
      Significant changes were observed for a number of the self-report instruments, including the Physical Function Scale of the Swiss Spinal Stenosis Questionnaire (P=.007), general health (SF-36; P=.008), role-limitation emotional (SF-36; P=.04), leg pain intensity (visual analog pain scales; P=.05), and presence of leg weakness (P=.008) (see table 3). Nonsignificant improvements were observed in walking capacity (SPWT), back pain intensity, and Symptom Severity Scale of the Swiss Spinal Stenosis Questionnaire.
      Of the statistically significant changes observed, the only 2 that met published values for MCID were the SF-36 general health and role-limitation emotional scales. The mean change of .92cm in leg pain intensity did not meet either value for MCID suggested in the literature (1.620 or 521). However, 59% did report an improvement of 1.6 or greater in leg pain. Similarly, although the mean change of 0.3 on the Physical Function Scale did not meet the suggested MCID of 0.5, 13 subjects (76%) did report improvement, while 2 (11.8%) reported no change and 2 (11.8%) reported worse physical function. Of the 13 reporting improvement on the Physical Function Scale, 5 reported a clinically important change (>0.5) while 6 reported a change of .40 and 2 reported a change <.40.
      When asked to rate their overall satisfaction with the result of their injection on a 7-point Likert scale anchored from 1 (very satisfied) to 7 (very dissatisfied), 6 participants were either a little bit, somewhat, or very satisfied, 4 were neutral, and 7 were either a little bit, somewhat, or very dissatisfied. Fig 1, Fig 2, Fig 3 demonstrate individual changes in overall activity counts, average daily activity counts, and Swiss Physical Function Scale scores from pre- to postinjection, coded as either satisfied (a little bit, somewhat, or very satisfied) or neutral/not satisfied (neutral, a little bit, somewhat, or very dissatisfied). No patterns emerged on the basis of satisfaction for any of these variables.
      Figure thumbnail gr1
      Fig 1Individual changes for total activity counts. Gray lines—reported being neutral or not satisfied with the overall results of the injection. Black lines—reported being satisfied with the overall results of the injection.
      Figure thumbnail gr2
      Fig 2Individual changes for average daily activity counts. Gray lines—reported being neutral or not satisfied with the overall results of the injection. Black lines—reported being satisfied with the overall results of the injection.
      Figure thumbnail gr3
      Fig 3Individual change in the Physical Function Scale. Physical Function Scale of the Swiss Spinal Stenosis Questionnaire (a higher score indicates worse physical function). Gray lines—reported being neutral or not satisfied with the overall results of the injection. Black lines—reported being satisfied with the overall results of the injection.

      Discussion

      This is the first study of which we are aware examining the effect of ESI for LSS on objectively measured physical activity (performance) in day-to-day life. Although no other studies to date have evaluated performance, self-report outcomes from the present study corroborate findings from other studies demonstrating improvements in pain and self-reported function with fluoroscopically guided ESI for LSS. For example, in a prospective cohort study of ESI for LSS, Botwin et al
      • Botwin K.P.
      • Gruber R.D.
      • Bouchlas C.G.
      • et al.
      Fluoroscopically guided lumbar transforaminal epidural steroid injections in degenerative lumbar stenosis: an outcome study.
      reported improvements at 2 months and 1 year in pain, function (Roland Morris 5-point scale), and self-reported standing/walking tolerance. In another study, Botwin et al
      • Botwin K.
      • Brown L.A.
      • Fishman M.
      • et al.
      Fluoroscopically guided caudal epidural steroid injections in degenerative lumbar spine stenosis.
      showed significant improvements in function (ODI), standing/walking tolerance, and pain at 6 weeks, 6 months, and 1 year. Similarly, in a retrospective review of 95 patients with LSS, Barre et al
      • Barre L.
      • Lutz G.E.
      • Southern D.
      • et al.
      Fluoroscopically guided caudal epidural steroid injections for lumbar spinal stenosis: a restrospective evaluation of long-term efficacy.
      showed pain improvement of 50% or more in 35% of the patients and functional improvement (Roland Morris) in 36%. Cooper et al
      • Cooper G.
      • Lutz G.E.
      • Boachie-Adjei O.
      • et al.
      Effectiveness of transforaminal epidural steroid injections in patients with degenerative lumbar scoliotic stenosis and radiculopathy.
      found that 59.6% of the subjects had successful outcome at 1 week, including improvements in pain, pain medication amounts, symptom severity, and physical function. Finally, in a study of 140 patients, Delport et al
      • Delport E.G.
      • Cucuzzella A.R.
      • Marley J.K.
      • et al.
      Treatment of lumbar spinal stenosis with epidural steroid injections: a retrospective outcome study.
      found that 32% reported pain relief lasting up to 2 months and 53% reported functional improvement, and Ciocon et al
      • Ciocon J.O.
      • Galindo-Ciocon D.
      • Amaranath L.
      • et al.
      Caudal epidural blocks for elderly patients with lumbar canal stenosis.
      demonstrated up to 10 months of pain relief following ESI.
      However, as mentioned, there is a need for more objective measures of function when assessing outcomes of ESI for LSS. In the first study to objectively examine function in people undergoing ESI for LSS, Cosgrove et al
      • Cosgrove J.L.
      • Bertolet M.
      • Chase S.L.
      • Cosgrove G.K.
      Epidural steroid injections in the treatment of lumbar spinal stenosis: efficacy and predictability of successful response.
      measured changes in ambulatory capacity (6-min walk) and self-reported function (Swiss Spinal Stenosis Questionnaire). They found significant improvements in walking capacity, physical function, and symptom severity 6 weeks postinjection. On the basis of their research, Cosgrove
      • Cosgrove J.L.
      • Bertolet M.
      • Chase S.L.
      • Cosgrove G.K.
      Epidural steroid injections in the treatment of lumbar spinal stenosis: efficacy and predictability of successful response.
      suggest that relatively small improvements in walking capacity could translate to significant increases in the ability to participate in activities of daily living (performance). However, Cosgrove
      • Cosgrove J.L.
      • Bertolet M.
      • Chase S.L.
      • Cosgrove G.K.
      Epidural steroid injections in the treatment of lumbar spinal stenosis: efficacy and predictability of successful response.
      did not measure performance.
      Therefore, to determine the impact of ESI on performance in people with LSS, we measured a number of aspects of performance, including total activity, peak activity, duration of time spent in the various intensity ranges (sedentary, light, moderate, high), and average steps per day. We also assessed walking capacity with accelerometry (maximum continuous activity) and with the validated SPWT. Although all the performance and capacity variables improved at 1-week postinjection, none of the changes were statistically significant. On the other hand, significant changes were observed in self-reported physical function, and symptoms (leg pain and leg weakness), general health, and emotional health.
      The nonsignificant trend for increased ambulation in the community after injection (see fig 2) is hopeful, with all 17 participants increasing their average daily activity postinjection. However, only 59% of the subjects increased their average daily step count, and only 53% decreased the time spent in the sedentary range. At the same time, the Swiss Physical Function Scale detected significant change in perceived function, with 76% of the subjects reporting improvement postinjection. Although the mean change of 0.3 in the Physical Function Scale does not meet the MCID criteria of 0.5, when examined individually, 5 participants reported a clinically important change (>0.5) and 6 reported a change of .40. Although the published MCID for this scale is 0.5, it is possible that an improvement of 0.4 could be considered clinically significant on an individual basis. A similar pattern emerged for pain, where although the mean change of .92cm failed to meet the suggested MCID of 1.6, 59% reported an improvement greater than 1.6, suggesting that the majority of participants perceived a clinically important change in leg pain.
      A number of interpretations can be applied to explain the fact that a questionnaire (Swiss Physical Function Scale) showed significant changes in function while objective measures of the same function did not show statistically significant changes. It is highly unlikely that the validated activity monitor output is a less precise measure than subjective survey results. It is conceivable that the subjects had noticed a real change in pain and ability but had not yet changed their activity patterns. This begs the question of whether individuals would increase activity in the future without further intervention such as physical therapy or instruction to exercise. It is more likely that subjects perceived a change in function when in fact no significant change had occurred. It is noteworthy that the SF-36 “role emotional” and “general health” variables improved after the injection, both statistically and based on the suggested MCID values. Whether this was a placebo effect or a pharmacologic consequence of the corticosteroids, this improved emotional status could have a halo effect in which subjects perceived improvement in walking but were not actually walking significantly more.
      Regardless of whether, as prior work suggests,
      • Harrast M.A.
      Epidural steroid injections for lumbar spinal stenosis.
      • Cosgrove J.L.
      • Bertolet M.
      • Chase S.L.
      • Cosgrove G.K.
      Epidural steroid injections in the treatment of lumbar spinal stenosis: efficacy and predictability of successful response.
      epidural injections improve walking capacity and tolerance for rehabilitation, results of the present study suggest that injections may be inadequate on their own for significantly improving performance. Additional intervention is likely needed to actually change physical activity in the community following injection. Intervention could be simply time for the patient to change habits, instruction to exercise, or a more comprehensive rehabilitation assessment looking at medical, physical, and psychosocial barriers to performance. Specifics of effective postinjection rehabilitation may depend on the patient, but this concept is worthy of further research.
      Results of the present study also highlight the extreme sedentary nature of this population and provide strong rationale for an increased focus on performance. Persons taking fewer than 5000 steps per day are considered sedentary.
      • Tudor-Locke C.
      • Hatano Y.
      • Pangrazi R.P.
      • et al.
      Revisiting “how many steps are enough?”.
      The average step count in this study was 2544 at baseline and 2846 following injection. This sedentary nature is confirmed by the percentage of time spent in the sedentary activity range (89.5% at baseline and 88.6% postinjection), with close to 0% of activity counts in the moderate and high intensity ranges. The extreme sedentary nature of this group could theoretically be explained by the relatively high BMIs (see table 1), given that recent research has identified BMI as the strongest predictor of performance in people with LSS.
      • Tomkins-Lane C.C.
      • Holz S.C.
      • Yamakawa K.S.
      • et al.
      Predictors of walking performance and walking capacity in people with lumbar spinal stenosis, low back pain, and asymptomatic controls.
      However, in the present study, BMI was not correlated with baseline performance or change in performance. Research is warranted to clarify the relation between BMI and performance and to determine whether BMI modulates the effect of injection (or other treatments) on performance in people with LSS.
      Regardless of the cause, sedentary behavior poses great risk for the development of diseases of inactivity and suggests that this population is likely not meeting the minimum amount of moderate intensity physical activity recommended for by the American College of Sports Medicine.
      • Chodzko-Zaijko W.J.
      • Proctor D.N.
      • Fiatarone Singh M.A.
      • et al.
      Exercise and physical activity for older adults.
      Therefore, in addition to limitations in mobility, and risk of obesity, people with LSS are potentially at increased risk for a number of metabolic and cardiovascular diseases.

      Study Limitations

      A randomized, blinded design would likely strengthen the findings of the present study. In addition, we followed patients only at days 7 to 14 postinjection. A longer follow-up may have shown greater changes in capacity and performance resulting from postinjection rehabilitation efforts or from altered habits. Research is warranted to examine changes in performance following injection with longer follow-up periods. It is unlikely that the sample size was too small to detect changes in activity, as the study was powered to detect significant change with 15 subjects, and we tested 17.

      Conclusions

      While patients perceived improvements in pain and function following injection, these improvements were not reflected in significant changes in objective measures of performance or capacity. Future studies on the effectiveness of epidural injections, surgery, and other interventions will continue to find value in subjective measures of pain, quality of life, and other outcomes. However, with modern technology, walking performance in the community is no longer a subjective variable in outcomes research. The use of activity monitors to objectively measure this important outcome can result in more rigorous validation of treatment, while simultaneously highlighting the potential need for additional postintervention rehabilitation aimed at improving performance.
      • a
        Actigraph, 49 E Chase St, Pensacola, FL 32502.
      • b
        Mathworks, 3 Apple Hill Dr, Natick, MA 01760-2098.
      • c
        SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.

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