Objective functional impairment in lumbar degenerative

CLINICAL ARTICLEJ Neurosurg Spine 33:4–11, 2020

For many years, patient-reported outcome measures (PROMs) have been used to assess the success and recovery of patients following spine surgery.8,25,26,31

Unfortunately, the subjectivity and lack of standardization inherent to many PROMs can negatively affect the clini-cal decision-making process.17,27 Even though the evolu-tion from physician-based to patient-reported outcome

measurements was necessary to obtain more independent and less biased measures to assess treatment results in the era of evidence-based medicine, it has been shown that PROMs also have their limitations. For example, the per-ception of patients’ health status by the surgeons and by the patients themselves may differ, which can reduce the reliability of health parameter measurements during pre-

ABBREVIATIONS BSS = baseline severity stratification; DDD = degenerative disc disease; HRQOL = health-related quality of life; LDH = lumbar disc herniation; LSS = lumbar spinal stenosis; MCID = minimum clinically important difference; OFI = objective functional impairment; PROM = patient-reported outcome measure; RC = regression coefficient; RMDQ = Roland-Morris Disability Questionnaire; TUG = timed-up-and-go; VAS = visual analog scale; 5R-STS = five-repetition sit-to-stand; 6WT = six-minute walking test. SUBMITTED September 17, 2019. ACCEPTED December 16, 2019.INCLUDE WHEN CITING Published online February 21, 2020; DOI: 10.3171/2019.12.SPINE191124.

Objective functional impairment in lumbar degenerative disease: concurrent validity of the baseline severity stratification for the five-repetition sit-to-stand testAnita M. Klukowska, BSc,1,2 Marc L. Schröder, MD, PhD,1 Martin N. Stienen, MD, FEBNS,3 and Victor E. Staartjes, BMed1,3,4

1Department of Neurosurgery, Bergman Clinics, Amsterdam, The Netherlands; 2School of Medicine, University of Nottingham, United Kingdom; 3Department of Neurosurgery, Clinical Neuroscience Center, University Hospital Zurich, University of Zurich, Switzerland; and 4Amsterdam UMC, Vrije Universiteit Amsterdam; and Neurosurgery, Amsterdam Movement Sciences, Amsterdam, The Netherlands

OBJECTIVE The five-repetition sit-to-stand (5R-STS) test provides a new dimension of clinical assessment by cap-turing objective functional impairment (OFI). Through the utilization of data from two prospective studies, the authors sought to evaluate the concurrent validity of the proposed 5R-STS baseline severity stratification (BSS) for OFI with the following levels based on time to completion in seconds: none, ≤ 10.4; mild, 10.5–15.2; moderate, 15.3–22.0; and se-vere, > 22.0 seconds.METHODS Patients with degenerative diseases of the spine performed the 5R-STS test and completed visual analog scales (VASs) for back and leg pain, the Oswestry Disability Index (ODI), the Roland-Morris Disability Questionnaire (RMDQ), and EQ-5D questionnaires. The degree of OFI severity was assessed based on the previously proposed BSS, and its association with patient-reported scales was evaluated using ANOVA as well as crude and adjusted linear regres-sion models.RESULTS Our sample included 240 patients, of whom 101 exhibited no OFI, whereas 80, 34, and 25 were judged to have mild, moderate, and severe OFI, respectively. A higher baseline severity was strongly associated with loss of work-ing ability (p < 0.001), as well as results of all patient-reported scales (p ≤ 0.001), with the exception of the VAS for leg pain (p = 0.556). Crude and adjusted regression analyses corroborated these findings, although only patients with mod-erate and severe OFI as judged by using the 5R-STS BSS demonstrated clinically relevant differences compared with patients without OFI.CONCLUSIONS The degree of OFI—based on the 5R-STS BSS—is strongly associated with measures of back pain, subjective functional impairment, and health-related quality of life. However, leg pain severity is not reflected within the dimension of OFI measured by the 5R-STS. The proposed BSS appears to be a concurrently valid and clinically relevant measure of OFI in patients with degenerative spinal pathologies.https://thejns.org/doi/abs/10.3171/2019.12.SPINE191124KEYWORDS objective functional testing; functional impairment; degenerative disc disease; lumbar spinal stenosis; lumbar disc herniation

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and postoperative management.24 Recently, PROMs have been evolving, leading to the establishment of instruments such as the PROMIS (Patient-Reported Outcomes Mea-surement Information System) computer adaptive test of physical function, which presumably takes less time and uses fewer questions and thus decreases the burden for the patient. These instruments have the potential to improve the assessment of patients and are already being intro-duced in the clinical workspace.2,22

Objective tests of function, such as the timed-up-and-go (TUG), six-minute walking test (6WT), and five-repetition sit-to-stand (5R-STS) test, can account for symptoms and signs that the available PROMs might miss, such as mobil-ity restrictions resulting from foot drop and limping.13 Ad-ditionally, patients are more drawn to objective functional testing rather than to subjective questionnaires.15 Overall, the quick completion, good reliability, and straightforward interpretation of tests for objective functional impairment (OFI) have the potential to be of great benefit when these tests are used alongside PROMs.16,29,32

The 5R-STS test has recently been used to examine pa-tients with degenerative pathologies of the lumbar spine.30 Previously, this test had already been successfully used in patients with other disorders, such as stroke, chronic ob-structive pulmonary disease, and Parkinson’s disease, but the literature on its utilization in the care of patients with degenerative spinal pathologies remains limited.6,14,21 Even though the 5R-STS test has been established as an easy, valid, and reliable assessment of OFI, little is known about its responsiveness and clinical interpretability. A baseline severity stratification (BSS) for patients with degenerative lumbar spinal disease has been proposed, which catego-rizes the 5R-STS test times of 10.5–15.2, 15.3–22.0, and ≥ 22.0 seconds as indicating mild, moderate, and severe OFI, respectively (Table 1). Patients with a test time of up to 10.4 seconds were regarded as having no relevant OFI.30

The 5R-STS test with its severity stratification has sub-stantial potential to improve the assessment of patients with spinal pathologies by providing a new form of objec-tive measurement. As of yet, the concurrent validity of the aforementioned BSS in relation to conventional PROMs has not been well established.20 The purpose of this study was to assess the concurrent validity of the 5R-STS BSS in patients with lumbar degenerative diseases by using data from two prospective studies.

MethodsOverview

We used data from two prospective cohort studies, conducted between October 2017 and June 2018, for which consecutive patients scheduled for lumbar surgery were seen at a Dutch specialized outpatient spine surgery clinic. Recruitment for the second study directly followed the termination of the first. Each participant completed the questionnaires immediately after performing the 5R-STS test in the consultation room. The two prospective studies (clinicaltrials.gov identifiers NCT03321357 and NCT03303300) were approved by the local institutional review board (Medical Research Ethics Committees Unit-ed, registration numbers W17.107 and W17.134) and were

conducted according to the Declaration of Helsinki. In-formed consent was obtained from all participants.

Study PopulationAll enrolled patients were candidates for surgery and

were assessed during outpatient consultations. Inclu-sion criteria were the presence of lumbar disc herniation (LDH), lumbar spinal stenosis (LSS), lumbar spondylolis-thesis, degenerative disc disease (DDD), or synovial facet cyst(s), requiring surgical treatment. Patients with hip or knee prosthetics and those requiring walking aides were excluded to eliminate these confounders.

Testing ProtocolThe 5R-STS test is the most common physical test of

function used during the evaluation of patients with de-generative spinal conditions.1,2,31 It was performed in a standardized fashion, as previously described.14,30 Partici-pants—wearing stable shoes—were asked to sit down on an armless chair of standard height (48 cm) with a hard seat, firmly placed against a wall. They were instructed to fold their arms across their chest and to keep their feet flat on the ground. To become familiar with the maneu-ver, participants were asked to once stand up fully and sit back down again without any assistance from their upper limbs. If assistance was required, the test was abandoned. Otherwise, participants were asked to stand up fully and sit down again, landing on the seat firmly, 5 times as fast as possible, starting on the command “go.” Using a stop-watch, the examiner timed the 5 repetitions from the initial command to the completed fifth stand. This time was re-corded as the participant’s score. If the patient performed the test in 30 seconds or more, this timing was captured, and the test score was recorded as 30 seconds.14,30

Outcome MeasuresPatients were asked to complete questionnaires contain-

ing baseline sociodemographic data, as well as the follow-ing numeric rating scales: visual analog scale (VAS) for back and leg pain severity, validated Dutch versions of the Oswestry Disability Index (ODI), the Roland-Morris Dis-ability Questionnaire (RMDQ), and EuroQOL-5D (EQ-5D) questionnaires—containing the EQ-5D index and the EQ-VAS—to capture subjective functional impairment and health-related quality of life (HRQOL), respectively.

The multidimensional ODI is among the most com-monly utilized PROMs in the management of spinal dis-orders.4 Therefore, the baseline ODI score was chosen as the primary outcome measure in this study.

Statistical AnalysisContinuous variables are reported as means ± standard

deviations (SD), and categorical variables as numbers and percentages. The previously described BSS was used to grade the severity of the patient’s OFI at baseline.30 We assessed intergroup differences in baseline demograph-ic and disease-specific factors using a one-way ANOVA. Linear regression models were fitted to assess the impact of the severity grading on included subjective PROMs with “no OFI” as the reference category. As done in a


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previous study, crude and multivariate regression models, adjusted for age, sex, BMI, surgical procedure, working status, and smoking status, were constructed to correct for potential confounders.30,32 The assumptions of the general-ized linear models were evaluated, and the model fit was quantified by the R2 values. Based on the R2 observed in the univariate analysis relating OFI to the ODI, a post hoc power analysis was performed. All analyses were carried out in R version 3.5.1 (R Foundation for Statistical Com-puting). A p ≤ 0.05 on two-tailed tests was considered sta-tistically significant. The statistical code is available in the Supplementary Material.

ResultsThe study included 288 adult patients. Forty-eight pa-

tients did not fully complete the questionnaire and were therefore excluded from the final analysis. OFI was present in 139 of the remaining 240 patients (58%; Fig. 1). Eighty (33%), 34 (14%), and 25 (10%) patients were categorized as having mild, moderate, and severe OFI, respectively. The remaining 101 patients (42%) were judged to have no OFI.

Detailed baseline characteristics are provided in Table 2. The lack of ability to work was significantly associated with a higher degree of OFI (p < 0.001). Namely, < 30% of patients with mild OFI, < 20% of patients with moderate OFI, and none of the patients with severe OFI were fully able to work. In addition, age differed significantly among the OFI BSS groups (p = 0.029). The remaining patient characteristics, including sex, BMI, smoking status, prior spine surgery, duration of symptoms, underlying spinal pathology, and affected spinal levels, were well balanced across the 4 OFI categories.

For each 1-step increase in the 5R-STS BSS, we noticed an increase in subjective low-back pain severity (VAS back pain, p < 0.001) and functional disability (ODI and RMDQ, both p < 0.001), as well as a decrease in HRQOL (EQ-5D index and EQ-VAS, both p = 0.001; Fig. 2). The only measure for which this relationship was not observed was VAS leg pain severity (p = 0.556). Additionally, there was no association between analgesic drug use and OFI severity (p = 0.660; Table 3).

The magnitude of change in each PROM with every 1-step increase in OFI BSS (Table 4) was quantified using a linear regression model. Compared to patients without OFI, those with mild, moderate, and severe OFI scored

2.57 (95% CI −2.06 to 7.20), 12.05 (95% CI 5.92–18.18), and 19.43 (95% CI 12.51–26.33) points higher on the ODI, respectively. The increase in ODI was significant (p < 0.001) for both moderate and severe OFI. The R2 calcu-lated for the univariate analysis of the primary outcome measure was 0.14. The post hoc power analysis demon-strated a power of 1 − b = 0.99 for the primary outcome measure analysis.

We have additionally performed a subgroup analysis for patients with LDH (Supplementary Table S1) and for those with LSS (Supplementary Table S2), which can be found in the Supplementary Material.

DiscussionWe set out to validate the previously proposed OFI

BSS—based on 5R-STS test values—in a sample of 240 surgical candidates with degenerative spinal conditions who filled out several commonly used PROMs. The use of the BSS for objective functional tests had been suggested previously, and here we used predefined cutoff values for the 5R-STS test, as recently reported.30,32 Our analysis demonstrates that the 5R-STS test and the proposed sever-ity stratification can be used to objectively assess function, as this test demonstrates good concurrent validity with multiple subjective outcome measures, including pain, disability, and HRQOL.

Particularly strong relationships were identified be-tween OFI and VAS back pain, RMDQ, ODI, and EQ-5D index scores. Patients with mild, moderate, and severe OFI had respective increases in their VAS back pain scores that were within the range of the commonly accepted mini-mum clinically important difference (MCID; 1.2 points) for VAS back pain.5 Similarly, patients categorized as having moderate or severe OFI had increases in ODI and RMDQ that were within the range or even surpassed the respective MCIDs (ODI 12.8 points; RMDQ 5.0 points), although this was not true for patients with mild OFI.5,19

TABLE 1. 5R-STS baseline severity stratification proposed by Staartjes and Schröder

5R-STS Baseline Severity StratificationOFI Severity Test Time (sec)

None ≤10.4Mild 10.5–15.2Moderate 15.3–22.0Severe >22.0

Modified with permission from Staartjes VE, Schröder ML: The five-repetition sit-to-stand test: evaluation of a simple and objective tool for the assess-ment of degenerative pathologies of the lumbar spine. J Neurosurg Spine 29:380–387, 2018.30

FIG. 1. Proportion of patients within each OFI group as categorized by the proposed BSS of 5R-STS test times.


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The HRQOL measured by the EQ-5D index also showed significant reductions, although only in patients with OFI. Studies analyzing other objective tests, such as the TUG test, also identified similar relationships between those variables.32 These findings demonstrate that tests of OFI can reflect a range of PROMs to a significant extent.

In the regression analysis only VAS back pain had a statistically significant relationship with mild OFI. This finding may be explained by the similarities in baseline demographics of patients within our cohort without OFI and those with mild OFI. It also suggests that both groups of patients may present very similarly. Categorization of a patient as having mild OFI based on 5R-STS testing may thus be of minor clinical relevance, as opposed to mod-erate or severe OFI, which demonstrated relevant statisti-cally significant and potentially clinically relevant effect sizes in our study. Whether mild OFI has any predictive validity for outcomes after surgery remains to be deter-mined.

The 5R-STS test integrates the overall state of a pa-tient’s neuromusculature; however, leg pain severity grad-ed using a VAS did not significantly correlate with any OFI BSS results. The majority of patients had a disc herni-ation at L5–S1. Radiculopathy is one of the most common symptoms in such patients.33 Therefore, it would seem that pain ought to increase as functional impairment becomes more pronounced. It may be argued that—among patients with LDH—there may be subgroups of patients in whom motor deficits have occurred with painless nerve compres-sion, and vice versa. Lipetz suggested that absence of pain may be indicative of less reversible axonal injury, which would point to a more established motor component rather than a temporary inflammatory state.18 Moreover, the ap-propriateness of performing the 5R-STS test may depend on the origin of the patient’s pain. A recent comprehensive systematic review on objective functional testing in lum-bar spinal patients suggested that the 5R-STS test should be the preferred method of evaluating OFI in patients with

TABLE 2. Basic demographic and disease-specific data for patients with lumbar degenerative disease with and without OFI

Characteristic No OFI (n = 101) Mild OFI (n = 80) Moderate OFI (n = 34) Severe OFI (n = 25) p Value

Age, yrs 48.0 ± 14.5 50.5 ± 13.4 43.3 ± 11.5 43.8 ± 11.4 0.029*Sex 0.073 Female 43 (42.6) 46 (57.5) 18 (53.0) 8 (32.0) Male 58 (57.4) 34 (42.5) 16 (47.0) 17 (68.0)Ability to work <0.001* Full 26 (25.7) 23 (28.6) 6 (17.6) 0 (0) Limited 32 (31.7) 17 (21.3) 2 (5.9) 7 (28.0) Unable 43 (42.6) 40 (50.1) 26 (76.5) 18 (72.0)BMI, kg/m2 25.1 ± 3.0 25.5 ± 2.9 25.8 ± 3.7 25.2 ± 4.0 0.684Smoking status 0.230 Active smoker 24 (23.8) 24 (30.0) 9 (26.5) 7 (28) Ceased smoking 33 (32.7) 23 (28.7) 10 (29.4) 7 (28) Never smoked 44 (43.5) 33 (41.3) 15 (44.1) 11 (44)Prior spine surgery 18 (17.8) 17 (21.3) 7 (20.6) 8 (32.0) 0.483History of pain 0.193 None–6 wks 3 (3.0) 4 (5.0) 1 (3.0) 0 (0) 6 wks–6 mos 33 (32.7) 31 (38.8) 18 (52.9) 14 (56.0) 6 mos–1 yr 65 (64.3) 45 (56.2) 15 (44.1) 11 (44.0) >1 yr 0 (0) 0 (0) 0 (0) 0 (0)Indication 0.419 Disc herniation 70 (69.3) 56 (70.0) 29 (85.3) 19 (76.0) Stenosis 21 (20.7) 16 (20.0) 2 (5.9) 3 (12.0) DDD 4 (4.0) 4 (5.0) 2 (5.9) 3 (12.0) Spondylolisthesis 6 (6.0) 4 (5.0) 1 (2.9) 0 (0)Index level 0.264 L2–3 2 (2.0) 4 (5.0) 0 (0) 1 (0.04) L3–4 16 (15.8) 7 (8.8) 1 (3.0) 1 (0.04) L4–5 34 (33.7) 35 (44.7) 13 (38.2) 11 (44.0) L5–S1 49 (48.5) 34 (42.5) 20 (58.8) 12 (48.0)

Values are presented as mean ± SD or number of patients (%) unless otherwise indicated.* p ≤ 0.05.


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axial back pain, while the 6WT and TUG test may be bet-ter for assessment of neurogenic claudication (LSS) and radiculopathy (LDH), which concurs with our findings.31

The findings of correlations between all of the inves-tigated conventional PROMs but the VAS leg pain test suggests that the OFI BSS test is not simply an identical reflection of subjective outcomes but rather a new dimen-sion in assessment of patients. Within seconds, it provides a rough but valuable overview of all relevant aspects of patient outcomes—pain, functional ability, and quality of life.31 It is known that there are associations between in-creased weakness and worse functional outcomes as well as recovery times.1,12 Those results suggest that severity of functional impairment may not be directly reflected in the amount of experienced pain. The sheer complexity of the nature of pain and its subjective perception may be explained via the biopsychosocial model of pain and ill-ness, first introduced by Engel in 1977.7 Long-term pain

has been shown to induce changes in the structure and function of the anterior cingulate cortex, which is respon-sible for the affective response to pain, reinforcing the in-tricate relationship between physical pain, emotions, and thoughts highlighted in Engel’s model.3 Recently it has been suggested that healthcare professionals often under-estimate patient pain, and it appears that the underesti-mation becomes more pronounced with increasing pain severity.28 Moreover, perception of pain by the patients themselves can change over time. It was shown that pa-tients who experience pain for long periods of time ac-quire an above-average pain threshold.23 This could apply to our cohort, given that most of the included individuals had experienced pain for more than 6 months.

Finally, the OFI BSS may also allow healthcare profes-sionals to assess any changes in functional impairments after surgery and monitor recovery, which has already been demonstrated in studies of other objective functional

TABLE 3. PROM scores of pain, functional impairment, and HRQOL of patients with lumbar degenerative disease with or without OFI

Characteristic No OFI (n = 101) Mild OFI (n = 80) Moderate OFI (n = 34) Severe OFI (n = 25) p Value

RMDQ 10.12 ± 5.14 11.49 ± 4.82 15.91 ± 4.76 16.88 ± 3.72 <0.001*ODI 40.65 ± 5.14 43.22 ± 4.82 52.71 ± 4.76 60.08 ± 3.72 <0.001*VAS back pain 4.88 ± 2.88 6.28 ± 2.28 7.21 ± 2.17 7.24 ± 2.40 <0.001*VAS leg pain 7.41 ± 1.93 7.31 ± 1.82 7.59 ± 2.05 7.92 ± 2.22 0.556EQ-5D index 0.43 ± 0.30 0.44 ± 0.29 0.23 ± 0.24 0.13 ± 0.25 0.001*EQ-VAS 53.21 ± 17.58 50.05 ± 16.71 47.62 ± 19.93 40.52 ± 18.63 0.001*Analgesic drug use, no. (%) 0.660 Daily 74 (73.3) 57 (71.3) 29 (85.3) 20 (80) Weekly 9 (8.9) 9 (11.2) 2 (5.9) 3 (12) Not regularly 18 (17.8) 14 (17.5) 3 (8.8) 2 (8)

Large effect sizes were observed for all outcomes except VAS leg pain severity and analgesic drug use. Values are presented as mean ± SD or number of patients (%) unless otherwise indicated.* p ≤ 0.0.

FIG. 2. Box plots demonstrating baseline PROMs stratified by the proposed BSS. The PROMs analyzed included the ODI (A), RMDQ (B), and VAS back pain (C) and leg pain (D) severity, as well as the EQ-5D index (E) and EQ-VAS (F). Median values (horizontal line), interquartile ranges (boxes), range (whiskers), and extreme outliers (circles) are shown.



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tests.10,11 However, an MCID for 5R-STS test results has not yet been established.11 The simplicity of the 5R-STS test and the relative quickness with which it can be con-ducted is advantageous for patients, who can perform it and even monitor their functional state at home.15,29 Using the 5R-STS test alongside conventional PROMs has the potential to be of great benefit in the assessment of patients with degenerative pathologies of the lumbar spine.

LimitationsThe calculated high statistical power for this study

requires a word of caution, as some of the revealed sta-tistically significant relationships may not be of clinical relevance. For this reason, the confidence intervals of the regression coefficients (RCs) should be regarded as more informative than the respective p values.

Additionally, our results should be used as a general validation for a range of degenerative lumbar pathologies, but not as a disease-specific validation. As 72.5% of the included cohort suffered from LDH, the results are closest to being disease-specific for LDH patients. However, the significant correlation with PROMs ought to encourage further research to validate the 5R-STS test for each of

the aforementioned currently less frequently included con-ditions. Prior similar analyses also included heterogenous samples because tests of OFI to assess spinal pathologies have been introduced only within the past couple of years, and in initial validation they were first applied to a broader spectrum of conditions.9,32

A high proportion of patients in this study reported daily use of analgesic medication, which may have influ-enced the results of both PROMs and objective outcome measures such as the 5R-STS test. The exact impact of pain medication on the 5R-STS test or on other objective tests of function is currently unknown.31 Moreover, not all confounders may have been accounted for, for example, the motivation of the patient to execute the test. No data on motor deficits or other presenting symptoms or comorbidi-ties were collected.

Patients with hip and/or knee prosthetics and walking aids were excluded from this study. As a consequence, some individuals with more severe disease may have been omitted. Such patients may have increased 5R-STS test time that is not necessarily caused by the lumbar degen-erative disease. If included in the study, the PROM scores related to the need for prostheses or walking aids would

TABLE 4. Linear regression model showing the relationship between OFI BSS and PROM scores for pain, functional impairment, and HRQOL in patients with lumbar degenerative disease

OFI BSS Severity Level

Univariate Analysis Multivariate AnalysisRC 95% CI p Value RC 95% CI p Value

RMDQ Mild 1.37 −0.06 to 2.79 0.061 1.24 −0.19 to 2.67 0.090 Moderate 5.79 3.91 to 7.68 <0.001* 4.93 2.98 to 6.88 <0.001* Severe 6.76 4.64 to 8.89 <0.001* 5.80 3.64 to 7.97 <0.001*ODI Mild 2.57 −2.06 to 7.20 0.277 1.65 −2.81 to 6.11 0.468 Moderate 12.05 5.92 to 18.18 <0.001* 8.31 2.23 to 14.38 0.008* Severe 19.43 12.51 to 26.33 <0.001* 15.91 9.16 to 22.66 <0.001*VAS back pain Mild 1.39 0.65 to 2.14 <0.001* 1.35 0.58 to 2.12 <0.001* Moderate 2.32 1.33 to 3.32 <0.001* 2.36 1.31 to 3.41 <0.001* Severe 2.36 1.24 to 3.48 <0.001* 2.29 1.12 to 3.45 <0.001*VAS leg pain Mild −0.09 −0.66 to 0.48 0.748 −0.10 −0.64 to 0.44 0.721 Moderate 0.18 −0.57 to 0.94 0.637 0.10 −0.64 to 0.84 0.794 Severe 0.51 −0.33 to 1.37 0.238 0.72 −0.10 to 1.54 0.087EQ-5D index Mild 0.01 −0.07 to 0.09 0.791 0.01 −0.07 to 0.09 0.800 Moderate −0.19 −0.30 to −0.08 <0.001* −0.15 −0.26 to −0.04 0.009* Severe −0.30 −0.42 to −0.17 <0.001* −0.26 −0.39 to −0.14 <0.001*EQ-VAS Mild −3.16 −8.37 to 2.05 0.236 −2.48 −7.69 to 2.73 0.351 Moderate −5.59 −12.49 to 1.31 0.114 −2.89 −9.97 to 4.20 0.425 Severe −12.69 −20.46 to −4.91 0.002* −11.27 −18.16 to −3.39 <0.001*

RCs are presented for each OFI BSS severity level compared to no OFI. Multivariate analysis was adjusted for age, sex, BMI, work ability, smoking status, and indication for surgery.* p ≤ 0.05.


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have led to the validation of the stratification for 5R-STS test for lumbar degenerative disease based on a sample of patients whose impairments may have been explained by unrelated conditions, which would have decreased the ac-curacy of the results. However, it is advisable for future validation studies that include such patients to explore the reason for the use of walking aids by patients, as in some instances it may be related to the investigated spinal pa-thology leading to the increased test times found for the study sample.

Prior assumption of the BSS for the 5R-STS test pro-posed in our previous studies may have introduced bias during study conduction.30 On the other hand, the catego-ries of OFI for the aforementioned test were based on non-parametric severity stratification, which can account for skewing of the raw test times.30 Additionally, the test was performed before the PROMs, for which the final score was calculated during the data analysis process. Therefore, it was highly unlikely that the investigator could have pre-dicted how the patient had to be scored for the study to achieve concurrent validity with the proposed BSS.

Lastly, the interrater agreement for the 5R-STS test was not assessed. Even though a sufficient interrater agreement of the test was already calculated previously in many pop-ulations, this variable may have had an influence on the reliability of the 5R-STS test.6,14,21,29

ConclusionsThe concurrent validity of the previously proposed

BSS for the 5R-STS test was evaluated in two prospec-tive cohorts. The categories of OFI of the 5R-STS per the proposed BSS were strongly associated with subjective measures of low-back pain, functional impairment, and HRQOL. A clinically important increase in the severity of certain PROMs was only observed in patients with moder-ate and severe OFI compared to patients without OFI. In addition, the BSS demonstrated little concurrent validity with VAS leg pain severity. In general, the 5R-STS test and its proposed BSS allows for a quick and solid estimate of OFI in patients with degenerative pathologies of the lum-bar spine.

AcknowledgmentsThe authors are grateful to all participating patients and to

Marlies P. de Wispelaere, MSc, for her efforts in clinical infor-matics.

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DisclosuresThe authors report no conflict of interest concerning the materi-als or methods used in this study or the findings specified in this paper.

Author ContributionsConception and design: Staartjes, Schröder, Stienen. Acquisition of data: Staartjes, Schröder. Analysis and interpretation of data: Klukowska. Drafting the article: Klukowska. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Statistical analysis: Staartjes, Klukowska. Adminis-trative/technical/material support: Staartjes. Study supervision: Staartjes.

Supplemental InformationOnline-Only ContentSupplemental material is available with the online version of the article.

Supplementary Material. https://thejns.org/doi/suppl/ 10.3171/ 2019. 12.SPINE191124.

CorrespondenceVictor E. Staartjes: Bergman Clinics, Naarden, The Netherlands. [email protected].




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Objective functional impairment in lumbar degenerative