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Subjective and Objective Measures of Symptoms, Function, and Outcome in Patients With Degenerative Spine Disease

The management of patients with degenerative diseases of the spine requires reliable measures of symptoms, function, and outcome. Choice of conservative or surgical therapy in this cohort is complex and depends on many factors, including the history, quality, and severity of pain; functional limitations; and healthrelated quality of life (HRQOL) (1,2). An accurate and thorough evaluation of both the subjective and objective condition is helpful to select adequate treatment for the individual patient (3). In recent years, subjective patientreported outcome measures (PROMs) in the form of questionnaires have been established as the gold standard for the clinical evaluation of spine patients (4). General pain measures, including the visual analog scale (VAS) or the numeric rating scale (NRS) for low back pain (LBP) or irradiating extremity (arm/leg) pain, are among the most commonly used PROMs. However, they are generic and not specific tools for spinal diseases (5). The Oswestry Disability Index (ODI), which is included in this review, is a prime example of an indepth validated PROM and represents one of the most established instruments for a variety of different diseases of the lumbar spine (6,7). There is a broad variety of degenerative spine diseases, some of which are unspecific, whereas others (eg, lumbar spinal stenosis [LSS]) present with characteristic symptoms (eg, neurogenic claudication) that can be addressed by diseasespecific tools (8). Cervical or thoracic degenerative spine disease may present with both radicular pain and/or myelopathy; outcome measures have to account for these different clinical manifestations (9). Apart from subjective PROMs, objective measures of function are gaining increasing attention in spine research and have found their way into clinical practice (8,10). Measurements like the Timed UpandGo (TUG) test and the motorized treadmill test (MTT) assess a patient’s objective functional impairment (OFI) and add a new dimension to the comprehensive patient evaluation (11). Because patients prefer objective functional tests rather than questionnaires and considering the continuous validation and standardization of objective outcome measures, we included the two most frequently applied tests of this relatively new field of outcome assessment in this review (8,12). Degenerative disease of the spine encompasses a wide range of different pathologies and diseasespecific symptoms. This leads to an even greater number of outcome measures that cannot all be included in the scope of this review. However, this article should provide the reader with a comprehensive summary of carefully selected instruments (Tables 1 and 2) (5,8,13).

the motorized treadmill test (MTT) assess a patient's objective functional impairment (OFI) and add a new dimension to the comprehensive patient evaluation (11). Because patients prefer objective functional tests rather than questionnaires and considering the continuous validation and standardization of objective outcome measures, we included the two most frequently applied tests of this relatively new field of outcome assessment in this review (8,12).
Degenerative disease of the spine encompasses a wide range of different pathologies and disease-specific symptoms. This leads to an even greater number of outcome measures that cannot all be included in the scope of this review. However, this article should provide the reader with a comprehensive summary of carefully selected instruments (Tables 1 and  2) (5,8,13).

SPINAL STENOSIS MEASURE (SSM) Description
Purpose. The SSM was developed in 1995 by Stucki et al as a short self-administered questionnaire to assess painrelated disability and health-related parameters in patients diagnosed with LSS (14). The SSM is also known as the Zurich Claudication Questionnaire, the Swiss Spinal Stenosis Questionnaire, or the Brigham Spinal Stenosis Questionnaire. The measure specifically addresses symptoms and functional deficits resulting from neurogenic claudication (14). It also includes an optional domain on patient satisfaction regarding the result of surgery. The SSM is one of the leading PROMs used by both spine surgeons and rheumatologists (5,15). 1

Psychometric information
Floor and ceiling effects. In one of the original articles, floor or ceiling effects in the range of 20% to 50% were observed for some items of the COMI Back before surgery (function and symptom-specific well-being) and after surgery (disability and function) (40).
Reliability. Several research groups examined the psychometric properties of the COMI Back in patients with various pathologies presenting with LBP. The test-retest reliability consistently scored highly, with an intraclass correlation coefficient (ICC) of 0.8 to 0.9 or more. High internal consistency for the core item index was shown for patients with chronic LBP (Cronbach's α = 0.90 or more); however, less was shown in patients with acute osteoporotic fractures (Cronbach's α = 0.64 or more) (38, 40,46).

Validity.
Good construct validity of the score was demonstrated by a moderate to high correlation with reference questionnaires, including the RMDQ, the SF-36, and the ODI (r = 0.60-0.79) (38, 46). The item symptom-specific well-being, however, showed little correlation to other measures (r = 0.25-0.31), which might indicate that this item delivers unique information that may be of importance to the multidimensional nature of the overall index (38).

Responsiveness.
Internal responsiveness corresponding with the SRM at the 12-month follow-up in a cohort of 91 patients undergoing surgery for LSS showed great responsiveness (SRM 1.44), which was similar to or better than the SSM average (1.50), the RMDQ (1.13), and the NRS pain (1.28) (29). In the same cohort, external responsiveness-meaning the strength of correlation between its change in scoring and the change in other outcome instruments-showed moderate correlation with the SSM (r = 0.62) and RMDQ (r = 0.43). In an area under the receiver operating characteristics (AUROC) curve analysis, good discriminative ability between good and bad outcomes was demonstrated (area under the curve of more than 0.83) (30).
Minimal clinically important differences. One of the original studies examining the COMI Back in 277 patients with LBP reported a minimum clinically important difference for improvement (MCID imp ) as a two-to three-point decrease, depending on the anchor used to indicate treatment success (38). In a group of 3056 patients undergoing spine surgery for a variety of indications, the groups' mean MCID imp at 12 months was −2.6 points, and the minimum clinically important difference for deterioration (MCID det ) was 1.2 points. AUROC curves of 0.88 for the MCID imp and 0.89 for the MCID det indicated good discriminative ability. The cutoffs for individual improvement and deterioration were −2.2 points or less (sensitivity 81%, specificity 83%) and 0.3 points or more (sensitivity 83%, specificity 88%), respectively (36).
Generalizability. Psychometric properties and sensitivity to change of the COMI Back are strong in patients with LBP from a variety of causes (38, 40,46,47). Thus, it can be applied to a broad range of patients with LBP.
Use in clinical trials. The COMI Back has been used in multiple clinical trials (48)(49)(50).

Critical appraisal of overall value to the rheumatology community
Strengths. The COMI Back is a short but independently and repeatedly validated outcome measure for a variety of different pathologies presenting with LBP and leg pain. It is easily accessible and is associated with a low burden for both patients and physicians.

Caveats and cautions.
As in other back-specific outcome measures (51,52), the COMI Back's values for the MCID det are lower than those for the MCID imp , indicating that the COMI is less responsive to deterioration than to improvement (36).
Clinical usability. The COMI Back has shown great psychometric properties and is brief enough to be practical for routine clinical use and quality management. Based on these values, it has been incorporated into the European EUROSPINE registry as an outcome questionnaire of choice (53).
Research usability. The availability and ease of administration is meant to encourage clinicians and researchers to collaborate in registries and research projects on a national and international level (54). However, on an international level, outcomes measures like the ODI and RMDQ are still more established (5).

NECK DISABILITY INDEX (NDI) Description
Purpose. Outcome research in cervical spine patients is historically less developed compared with lumbar spine patients (5,55). The NDI is one of the best established and most commonly used PROMs for chronic neck pain (56,57). Originally published in | 187 1991, it is also known as the Vernon-Mior Disability Index or the Neck Pain Disability Index (58,59).

Content.
The NDI measures pain and disability in patients with neck pain. The NDI covers the domains of pain intensity, personal care, lifting, work, headache, concentration, sleeping, driving, reading, and recreation.

Number of items. Ten items.
Response options/scale. Each of the 10 items are scored on a six-point Likert scale ranging from 0 (no pain/disability) to 5 points (maximal pain/disability).
Recall period for items. The questions refer to the current clinical condition and pain intensity. The exact time frame is not defined.

Cost to use. None.
How to obtain. Copies in English and other languages can be found in published sources or from the EUROSPINE Spine Tango registry website (https://www.euros pine.org/forms.htm) (56,58,59).

Practical application
Method of administration. The NDI is self-administered by patients using paper and pen.
Scoring. All 10 items are scored from 0 to 5. Numeric responses are summed up to a total score ranging from 0 (best) to 50 (worst). The developer and others recommend scoring the NDI out of 50 points. If three or more items are missing, the questionnaire is not valid. If two or fewer items are missing, the score should be normalized to 50 (58,59). Besides presenting raw test results, many groups have expressed the score as a percentage, ranging from 0% to 100% neck disability.

Score interpretation.
No consensus exists regarding score interpretation. The original developers suggested the following: scores between 0 and 4 represent no disability, scores between 5 and 14 represent mild disability, scores between 15 and 24 represent moderate disability, scores between 25 and 34 represent severe disability, and scores greater than 35 represent complete disability (56).
Respondent time to complete. The NDI is relatively short and simple to fill out. It can be completed by the patient in 3 to 8 minutes (56).
Administrative burden. The NDI requires no administration burden and takes less than 3 minutes to score by hand. No training necessary.
Translations/adaptations. The NDI was originally developed in English but has been culturally adapted and translated into several languages including German (60,61), Spanish (62)

Psychometric information
Floor and ceiling effects. Patients with baseline score in the lower 10th and the upper 90th percentile are subject to significant floor or ceiling effects, respectively. This is why caution is required when using the NDI to monitor outcome in these high-or low-performing patients (56,71,72).

Reliability.
A systematic review published in 2009 analyzed 41 studies that examined at least one aspect of the psychometric properties of the NDI. A high test-retest reliability was demonstrated in populations with both acute and chronic neck pain, with a reliability coefficient of more than 0.90 in most studies (56).
Validity. The NDI score correlates strongly (r of more than 0.70) with other neck disability measures, including the Neck Pain and Disability Scale, the Cervical Spine Outcome Questionnaire, the Disability Rating Index, and the VAS pain scale. Furthermore, high Cronbach's α scores of 0.70 to 0.96 show good internal consistency (56,57,60,70). The NDI is, however, only moderately correlated with both physical and mental aspects of general health as assessed by the SF-36 (56).
Responsiveness. The NDI has a good ability to detect changes over time. The SRM ranges from 0.60 to 0.95 in a systematic literature review (56).

Minimal clinically important differences. Reported
MCIDs range from 5 of 50 to 19 of 50 points (56). Neck pain of musculoskeletal origin seems to show a lower MCID (change of more than 5 points) compared with nerve-related pain (7-13.4 points) (56,73,74). It is important to understand that each MCID is disease specific and, accordingly, shows slight variations, but on average a change of 5 to 7 points on the NDI (10%-14%) can be considered a clinically meaningful change in pain and disability.
Generalizability. Because of its strong psychometric properties and its cross-validation in several languages, the NDI can be used in a variety of different patient populations with neck pain.
Use in clinical trials. The NDI has been used in multiple clinical trials (75,76).

Critical appraisal of overall value to the rheumatology community
Strengths. The NDI is a reliable, valid, and responsive measure in various populations. This includes patients with both acute and chronic conditions as well as patients with neck pain associated with musculoskeletal dysfunction, whiplash-associated disorders, and cervical radiculopathy (56,60).
Caveats and cautions. The MCID differs across study populations and publications, which complicates the standardized interpretation of NDI results over time in clinical practice and research (56). The NDI does not include psychosocial and emotional aspects, although these are quite common in patients with chronic neck pain (56). We recommend scoring the NDI out of 50 points, as originally proposed.
Clinical usability. The NDI is one of the most common PROMs for neck pain and is regularly used by rheumatologists, spine surgeons, and physiotherapists (13,56,57). More studies reporting MCIDs for specific pathologies and patient populations are required (56).
Research usability. The good psychometric properties support using the NDI in research on cervical spine or neck diseases.

OSWESTRY DISABILITY INDEX Description
We would like to refer to the article by Smeets et al (77) for a comprehensive description of the ODI. To avoid considerable redundancy, we provide only a brief overview and literature update on the ODI.
Purpose. The ODI assesses pain-related disability in patients with LBP associated with a wide range of causes/disorders. It is especially useful in patients with severe, persistent disability (6). Initially published in 1980 by John O'Brian (version 1.0), it has been modified several times (6,78,79). All versions of the ODI remain in use; however, not all have been subject to the same systematic validation as the original. The ODI version 2.0 developed by Fairbank et al is recommended for general use and has been adapted by various spine societies (6,7).

Content.
The ODI contains one item on pain intensity and nine items on activities of daily living (ADLs) (personal care, lifting, walking, sitting, standing, sleeping, sex life, social life, and traveling).

Number of items. Ten items.
Cost to use. No permission is required, and the questionnaire is free.
How to obtain. The ODI can be found in the original article (7).

Psychometric information
The ODI has been used in multiple clinical trials (32,80,81).

Critical appraisal of overall value to the rheumatology community
Clinical usability. The ODI is one of the most commonly used clinical measures of pain-related disability in a variety of pathologies of the lower back. The ODI has established psychometric properties, a high reliability and validity, as well as low respondent and administrative burden (77).

Research usability.
The ODI is one of the most frequently used outcome questionnaires for assessing and monitoring outcomes in both patients undergoing surgical or conservative care (5,82). It is frequently used as a comparator to validate other outcome measures.

ROLAND-MORRIS DISABILITY QUESTIONNAIRE Description
Similar to the ODI, we would like to refer to the article by Smeets et al (77) for a more comprehensive description of the RMDQ.
Purpose. Originally designed in 1983, the RMDQ assesses physical disability due to LBP (83). It has been extensively used for acute, subacute, and chronic LBP as well as sciatica in various clinical settings (84). Since its first publication, several modifications have been proposed to improve suitability for specific patients (eg, for those with sciatica). However, changes resulted only in minor improvements and reduced comparability (85). The use of the original 24-item RMDQ is therefore recommended (7,35).

Content.
The RMDQ assesses the execution of ADLs and common functions (housework, sleeping, dressing, mobility, appetite, etc). It does not exclusively contain items to rate physical disability but rates general impairment and health as well.
Number of items. Twenty-four items.

| 189
Cost to use. No permission is required, and the questionnaire is free.
How to obtain. Free download in different languages is available on the RMDQ website (www.rmdq.org/). A copy is attached in the original publication (7).

Critical appraisal of overall value to the rheumatology community
Clinical usability. Although it is nonspecific to any spine pathology, the RMDQ is one of the most established and thoroughly evaluated measures for patients with LBP. It has psychometric properties ranging from acceptable to good. However, scores and changes must be interpreted with caution because some items are poor-fitting, and the overall score does not have interval-level properties.
Research usability. Psychometric qualities are acceptable for use in research. Rasch analysis and examination of score distribution is recommended as part of statistical analysis (89) (see Tables 1 and 2).

OBJECTIVE OUTCOME MEASURES TIMED UP-AND-GO TEST Description
Purpose. The TUG is the most frequently applied objective task-based functional outcome measure in patients with lumbar degenerative disk diseases (DDDs) (8). It includes several activities that are difficult to perform for patients with painful conditions or disability resulting from lumbar DDD, eg, standing up, walking fast, changing direction, and sitting down (8,90).

Content.
The patient is asked to sit and lean back on an armchair, with arms resting on the armrests. On command, the patient should get up and walk as fast as possible to a line marked on the floor at 3 meters away from the chair. At this line, the participant should turn around, walk back to the chair, and sit down as quickly as possible. The examiner records the time (in seconds) between getting up and sitting down again.

Cost to use. None.
How to obtain. Measurement is possible with any commercial stopwatch. A smartphone application (TUG app) is available in multiple languages and conveniently measures and scores the TUG test based on normal population reference values. It can be downloaded free of cost in the Apple App Store (https:// itunes.apple.com/de/app/tug-app/id111 90877 07?mt=8) and the Android Play Store (https://play.google.com/store/ apps/detai ls?id=ch.webge aring.tugapp).

Practical application
Method of administration. The TUG test does not require any special equipment except for a chair, a timer, and 3 meters of unrestricted walking space. It is currently recommended that an examiner takes the patient's time; however, patient self-measurements have been found to be reliable for similar objective functional tests (91). Walking aids (cane, walker, etc) are permitted if required.

Scoring.
Results are traditionally expressed as raw test times (in seconds). Because raw TUG test times naturally vary, it is recommended to express TUG test results in a standardized manner for age and sex. Standardized OFI Z scores/T scores express a patient's deviation from the normal population mean and can be calculated conveniently using the TUG app (see How to obtain) (11,(92)(93)(94)(95).
Score interpretation. Expressing OFI as a standardized Z/T score prevents bias introduced by the high influence of the variables age and sex and can express disability on an interval scale (93,96,97). Alternatively, TUG test results can be stratified according to severity into no OFI (TUG test results are less than the upper limit of the normal population range [ULN]), mild OFI (the TUG test results are between the ULN and the 33rd percentile of the diseased population), moderate OFI (TUG test results are between the 33rd and 66th percentile of the diseased population), and severe OFI (TUG test results are greater than the 66th percentile of the diseased population) (11,95).
Administrative burden. The TUG requires very low administrative burden. Completion typically takes less than 1 minute. The administrative burden is lower than that of most PROMs, and the TUG test was preferred over a set of questionnaire-based PROM assessments by 60% to 70% of patients (12).

Psychometric information
Floor and ceiling effects. For discriminating subjects with healthy spines and patients with spine disease, the ULN was set as the 99th percentile of the normal population's TUG test results (11). In subsequent series that examined surgical candidates with lumbar DDD, a considerable proportion of candidates (approximately 60%) scored within the normal population range (no OFI). Thus, the standardized interpretation of TUG test values is likely to have a floor effect (11,95). There is no upper time limit for the TUG test, and the calculation of standardized OFI Z/T scores allows for the accurate determination of extreme disability without a ceiling effect. Responsiveness. Several studies demonstrated that the TUG test is sensitive to the postoperative change in function of a patient with DDD (92,94,98). The SRM is 0.51 in a sample of 123 patients with lumbar DDD who were examined before and 6 weeks after lumbar spine surgery (data not published).

Reliability
Minimum clinically important differences. In patients with lumbar DDD, a change in raw TUG test time of at least 3.4 s is considered a clinically meaningful change in function (94).
Generalizability. The TUG test has been used in a broad variety of pathologies of the lumbar spine (8). Only a few studies so far have focused on the psychometric properties of the TUG for a specific disease (eg, LSS) (99).
Use in clinical trials. The TUG has been used in multiple clinical trials (88,90,100,101).

Critical appraisal of overall value to the rheumatology community
Strengths. The TUG test is safe, fast, easy to conduct, and well appreciated by patients (12). It is the most thoroughly validated objective outcome measure to assess OFI in patients with degenerative disease of the lumbar spine (8). Its test result is (relatively) independent from the confounding influence of the variables age and sex (11), body mass index (101), and mental health status (102), but it takes disability resulting from lower extremity motor deficits into account (103).

Caveats and cautions.
The test cannot be applied to patients who are unable to ambulate (despite walking aid) because of severe pain or neurological deficits. There may be a significant influence of comorbidities (eg, hip or knee osteoarthritis, congestive heart failure, Parkinson's disease, etc), which renders interpretation of test results in these patients difficult.
Clinical usability. Quick to conduct and interpret without the need for special equipment, the TUG test can easily be integrated into clinical routine (administration by nursing staff, advanced practice providers/physician assistants, or physical therapists [PTs]). It should be noted that the TUG test correlated moderately with a broad range of different pain, disability, and HRQOL measures, indicating that the TUG test can provide a broad impression about the patient's general functional status. However, for an in-depth analysis of specific aspects of a patient's condition, the assessment may need to be supplemented with one or several PROMs (11).
Research usability. The strong psychometric properties of reliability and validity paired with the low administrative burden and high patient acceptance demonstrate that the TUG is an accurate and quick tool for the measurement of OFI in clinical spine research.

MOTORIZED TREADMILL TEST (MTT) Description
Purpose. In a recent systematic review, the MTT was the second-most frequently applied measure to determine OFI in patients with lumbar DDD (8). Because of the typically long treadmill protocols that challenge the walking capacity of participants, it has been primarily studied in patients with LSS and neurogenic claudication. The MTT has been used as an objective outcome measure in several randomized controlled trials and observational studies (8).
Content. The participant is instructed to walk on a calibrated treadmill, usually at a predefined protocol starting on a level surface. Different protocols in terms of speed, time, or incline exist without an accepted gold standard (8). Ambulation time and distance, walking speed, and time of onset or significant increase in symptoms are monitored as test results. Several studies proposed a protocol that starts with 10 minutes at 2 mph, increases to 2.5 mph for the next 5 minutes, and then increases to 3 mph for an additional 5 minutes (total of 20 minutes) (104,105). Some protocols remain at a constant speed between 2 and 2.5 mph for the complete duration of the test (between 15 and 30 min-| 191 utes) (106)(107)(108)(109)(110), whereas others instruct participants to walk at a maximum individually selected speed for up to 15 to 30 minutes (111)(112)(113)(114). Further individualized protocols exist (8).
Cost to use. The MTT requires the cost of special equipment (motorized treadmill), and PTs are needed to safely administer the test.
How to obtain. MTT protocols can be adopted using published literature. For different protocols, see the references above.

Practical application
Method of administration. The MTT requires a programmable motorized treadmill and trained personal to supervise protocol adherence and patient safety. In most programs, participants are allowed to hold one handrail for balance purposes. Using both handrails is restricted because it can improve walking capacity and speed in LSS by allowing the patient to bending forward (8,112,115). In the case that a patient does not tolerate the standard speed, it is reduced by the supervisor or the test is ended. Some studies use safety end points (eg, 85% of predicted maximal heart rate [220 − age]) as an additional reason for premature test termination (116). Some authors state that the additional information gained after 15 minutes of test time is negligible (117,118).

Scoring.
Test results derive from 1) the time to first symptoms (TTFS) for general pain and/or paresthesia, 2) total ambulation time (in minutes or seconds) and distance (in meters), and 3) maximum walking speed (in m/s).

Score interpretation.
All published studies so far have reported raw test results. No studies have expressed results in standardized fashion using Z-or T scores. Moreover, different walking protocols impede result comparisons across different studies (8).

Administrative burden. Test time is 15 to 30 minutes.
In addition, the patient needs to be instructed in written or verbal form, and some studies use a heart rate monitoring system. According to the specific walking protocol, results in different stages of the test can be recorded.

Psychometric information
Floor and ceiling effects. The authors are unaware of studies reporting on the MTT's floor or ceiling effects. However, a relatively poor discriminative capacity between subjects with healthy spines and patients with spine disease with low disability burden can be assumed (similar to the TUG test). A study by Tomkins et al showed that the MTT likely underestimates a patient's true walking capacity when compared with a different walking test (the self-paced walking test [SPWT]) (119).

Reliability.
The MTT showed a high to excellent intrarater reliability, both for TTFS (ICC = 0.90-0.98) and total ambulation time (ICC = 0.89-0.96) at 1.2 mph fixed or individually selected walking speed (120). Another group reported slightly lower intrarater reliability (ICC = 0.83) with a different protocol that simulated a gradual increase in walking speed (121).

Responsiveness.
Several studies have documented the MTT's good responsiveness to change in conservatively and surgically treated patients with lumbar spine disease; however, no SRMs are reported and between-study comparisons are complicated by different MTT protocols (117,122,123). Moreover, in a report of 32 patients undergoing surgery or conservative treatment for LSS, internal responsiveness was low and was significantly worse compared with the SPWT (effect size [ES] in time 0.17 min; ES in distance 0.09 m; ES in speed 0.11 km/h) (112).
Minimum clinically important differences. The authors are unaware of any studies reporting on the MTT's MCIDs.
Generalizability. Most studies applied the MTT to patients with LSS because of its ability to trigger symptoms and functional deficits characteristic of neurogenic claudication. Within the LSS population, good psychometric properties have been shown. However, the great variety of test protocols complicates generalizability of the results.
Use in clinical trials. The MTT has been used in multiple clinical trials (109,110,116).

Critical appraisal of overall value to the rheumatology community
Strengths. The MTT helps objectify functional impairment in LSS over time as well as before and after conservative or surgical treatment. It is validated and used in numerous studies.
Caveats and cautions. The MTT cannot be applied to patients who are unable to ambulate. Other comorbidities, especially hip/knee osteoarthritis and severe pulmonary and cardiac diseases, may represent significant confounders by limiting walking capacity or by making this exercise-based test medically inadvisable. A certain risk of frightening or even injuring patients who are elderly needs to be considered and might lead to test dropouts (124).
Clinical usability. As a measure of walking capacity, the MTT can provide a valuable impression of a patient's functional status, thereby supplementing PROM assessments, especially in patients with LSS. A drawback for the clinical use of the MTT is that it is comparably resource-intensive, requiring special equipment and trained personnel.
Research usability. There is sufficient evidence of the reliability and validity of the test. The MTT might increase our insight into the interaction of objective physiological walking capacity and subjective PROMs. However, the lack of a widely accepted standardized protocol and insufficient data on responsiveness and MCIDs hamper research usability and comparison between studies.

CONCLUSIONS
PROMs remain the current gold standard in evaluating patients with degenerative diseases of the spine. Ideally, they should become an integral part of any institution's patient evaluation, both for clinical practice and research (125,126). PROMs help to evaluate, monitor, and compare treatment results over time and across populations.
The considerable variability of spinal pathologies and their clinical presentation led to the development of various diseasespecific outcome measures, some of which are reviewed in this article (Tables 1 and 2). To remain concise and to not exceed the scope of this review, the authors acknowledge that there are several other important outcome measures that are not discussed. These include, for example, the Scoliosis Research Society Questionnaire 22, 23, and 30, assessing patients with spinal deformities; the (modified) Japanese Orthopaedic Association Myelopathy Scale, assessing patients with cervical spondylotic myelopathy; or the Copenhagen Neck Functional Disability Scale, assessing the level of functional disabilities in patients with neck pain. Other LBP-specific measures are the Low Back Pain Bothersome Scale, the Low Back Pain Impact Questionnaire, and the National Institutes of Health Low Back Pain Minimal Dataset. In addition, generic outcome measures (that are not disease-specific instruments for spinal pathologies), such as the Patient-Reported Outcome Measurement Information System measures, or HRQOL measures, such as the SF-12/SF-36 or the EQ-5D, have been extensively reviewed in the literature elsewhere (126,127). Other objective measures of function that exceed the scope of this paper but are systematically reviewed elsewhere include the SPWT, the 6-minute walking test (6WT), the five-repetition sit-tostand test, the shuttle walking test, and the Short Physical Performance Battery besides step counters (8,10,128,129).
It is clear that certain spinal diseases may require specific assessment tools. However, to enable comparison of pain and disability between individuals, disease populations, or studies, in the vast majority of patients, the use of a single PROM would suffice. Because of its good psychometric properties, popularity, and ubiquitous use, we recommend use of the ODI as the PROM of first choice in patients with degenerative diseases of the lumbar spine. For the same reasons, we recommend using the NDI in patients with degenerate cervical spine diseases presenting with acute or chronic neck pain.
Regarding the evaluation of pain/disability over time, a baseline assessment, followed by 3-month and 12-month follow-up assessments after the initiation of treatment appears reasonable. Recent research indicates that most functional recovery after surgery can be expected within 8 to 12 weeks (10).
The broader availability of modern technologies such as smartphones or wearable devices with global positioning systems (GPS), combined with patient demand for a more personalized and transparent care, drive the trend to construct detailed, accurate, and intelligible medical profiles based on objective activity data (10,130). Tests such as the TUG test, the MTT, or the SPWT are already established and validated objective outcome measures used in spine care and research and can complement PROMs and add a further dimension to an in-depth patient evaluation. Free smartphone applications that accurately measure OFI by determining walking capacity based on GPS coordinates (eg, the 6WT app) are currently validated in clinical trials and offer great potential for further advances in this field (129