SPINE Volume 40, Number 1, pp E23-E28 ©2014, Lippincott Williams & Wilkins
CERVICAL SPINE
Psychometric Properties of the Modified Japanese Orthopaedic Association Scale in Patients With Cervical Spondylotic Myelopathy Branko Kopjar, MD, PhD, * Lindsay Tetreault, BSc,† Suhkvinder Kalsi-Ryan, PhD,† and Michael Fehlings, MD, PhD†
Study Design. Prospective study. Objective. This study aims to determine the psychometric properties of the modified Japanese Orthopaedic Association (mJOA) scale. Summary of Background Data. Several outcome measures assess functional impairment and quality of life in patients with cervical myelopathy. However, a “gold standard” has not been established. One of the most widely accepted tools for assessing functional status is the mJOA scale. Methods. Two hundred and seventy-seven surgical patients with cervical spondylotic myelopathy were enrolled in the prospective cervical spondylotic myelopathy-North America study. Functional status was evaluated at baseline and at 6, 12, and 24 months postoperatively. The internal consistency of the mJOA was assessed by computing a Cronbach α for the total score and after removing 1 item at a time. Convergent validity and divergent validity were measured by correlating the mJOA with other assessment tools. The responsiveness of the scale was determined by comparing mJOA scores at baseline and 12 months after surgery and computing a Cohen effect size. Results. The internal consistency of the scale was moderate with a Cronbach α of 0.63. Sphincter dysfunction measured a different dimension than the other 3 scale components. The mJOA was correlated with the Nurick score (r = −0.625) but was
From the *Department of Health Services, University of Washington, Seattle, WA; and; †Division of Neurosurgery, Toronto Western Hospital, University of Toronto, University Health Network, Toronto, Ontario, Canada. Acknowledgment date: August 12, 2014. First revision date: September 29, 2014. Acceptance date: October 1, 2014. The manuscript submitted does not contain information about medical device(s)/drug(s). Funds were received from AO Spine for the collection of original data used in this work. Relevant financial activities outside the submitted work: grant, grants pending, consultancy. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivitives 3.0 License, where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially. Address correspondence and reprint requests to Michael G. Fehlings, MD, PhD, Division of Neurosurgery, Toronto Western Hospital, 399 Bathurst St, Ste 4WW-449, Toronto, Ontario M5T2S8, Canada; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000648 Spine
not associated with subscales of the Short-Form 36 that measure different constructs. These findings suggest convergent and divergent validity. The mJOA was responsive to change as reflected by a Cohen effect size of 1. Conclusion. The mJOA is a useful tool in the assessment of cervical spondylotic myelopathy and it should be adopted as the standard for evaluating functional status in this population. Key words: cervical spondylotic myelopathy, CSM, validation, outcome measures, mJOA. Level of Evidence: 3 Spine 2015;40:E23–E28
C
ervical spondylotic myelopathy (CSM) is a progressive degenerative spine disease and the most common cause of spinal cord impairment in adults worldwide.1 The successful management of CSM depends upon an early and accurate diagnosis, an objective assessment of impairment and disability, and an ability to predict outcome. In this field, quantitative measures are increasingly used by clinicians to grade functional and neurological status and to provide decision-making support.2 In addition, objective assessment tools allow clinicians to quantify myelopathy severity, predict outcome, and evaluate surgical benefits by tracking improvements throughout follow-up.3–5 Several outcome measures assess functional impairment and quality of life in patients with cervical myelopathy.6–10 A validated “gold standard,” however, has not been established, preventing the development of quantitative guidelines for CSM management.2 In this field, one of the most widely accepted tool for assessing functional status is the modified Japanese Orthopaedic Association (mJOA) scale.5 This 18-point investigator-administered scale separately addresses motor dysfunction of the upper extremity (MDUE) and motor dysfunction of the lower extremity (MDLE), sensory loss of the upper extremity, and sphincter dysfunction (SD) (Table 1). It was modified from the original Japanese Orthopaedic Association (JOA) scale proposed by Benzel et al11 to increase its applicability in the Western population.11 Some of the differences include that the modified scale has been translated into English and evaluates a patient’s ability to use Western cutlery rather than chopsticks. Although not well defined in the literature, www.spinejournal.com
E23
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E23
03/12/14 2:23 AM
CERVICAL SPINE TABLE 1. The Modified Japanese Orthopaedic
Association Scale
Motor dysfunction score of the upper extremity 0—Inability to move hands 1—Inability to eat with a spoon, but able to move hands
Psychometric Properties of the mJOA Scale • Kopjar et al
from 277 surgical patients with CSM. We anticipate that this work will enable the translation of previous and current research efforts into clinical practice. In addition, if proven both valid and responsive, we recommend that the mJOA be adopted as the standard method for evaluating severity and outcome in patients with CSM.
2—Inability to button shirt, but able to eat with a spoon
MATERIALS AND METHODS
3—Able to button shirt with great difficulty
Subjects
4—Able to button shirt with slight difficulty 5—No dysfunction Motor dysfunction score of the lower extremity 0—Complete loss of motor and sensory function 1—Sensory preservation without ability to move legs 2—Able to move legs, but unable to walk 3—Able to walk on flat floor with a walking aid 4—Able to walk up and/or down stairs with hand rail 5—Moderate-to-significant lack of stability, but able to walk up and/or down stairs without hand rail 6—Mild lack of stability but walks with smooth reciprocation unaided 7—No dysfunction Sensory dysfunction score of the upper extremities 0—Complete loss of hand sensation 1—Severe sensory loss or pain 2—Mild sensory loss 3—No sensory loss Sphincter dysfunction score 0—Inability to micturate voluntarily 1—Marked difficulty with micturation 2—Mild-to-moderate difficulty with micturation 3—Normal micturation
the mJOA seems to be a multidimensional tool that assesses 3 key and distinct components (upper limb dysfunction, lower limb dysfunction, and bladder dysfunction) of CSM. Yonenobu et al12 assessed the reliability of the JOA studying 29 patients with cervical myelopathy secondary to ossification of the posterior longitudinal ligament.12 Both the inter- and intraobserver reliabilities were high (0.81 and 0.84, respectively), indicating that the JOA scale is a reasonable and valuable tool for the assessment of patients with cervical myelopathy. Because the differences between the JOA and mJOA are substantial, it cannot be assumed that the mJOA carries the same psychometric properties. Despite its widespread use, this instrument has never been subjected to rigorous evaluation of reliability, responsiveness, and validity. This study aims to assess the internal consistency, dimensionality, validity, and responsiveness of the mJOA using data E24
www.spinejournal.com
Between December 2005 and September 2007, 277 patients were enrolled in the prospective multicenter AOSpine CSMNorth America study at 12 North American centers.13 Patients were asked to participate in this study if they were referred to a site’s orthopedic or neurosurgery department and if they met the following inclusion criteria: (1) aged 18 years or older; (2) presenting with symptomatic CSM with at least 1 clinical sign of myelopathy; (3) evidence of objective cervical cord compression on a magnetic resonance image; (4) no previous surgical treatment for myelopathy; and (5) absence of lumbar stenosis. Patients were not excluded on the basis of duration of symptoms, myelopathy severity, or prior conservative treatment. All patients received anterior or posterior decompression and reconstruction at their respective sites. The surgical approach, the number of operated segments, and whether or not to use instrumentation varied case by case and was determined by the attending surgeon. Postoperative rehabilitation was per standard of care at the treating institutions. Extensive data for each participating subject were collected at baseline, 6, 12, and 24 months, including demographic information, surgical summary, symptomatology, medical history, and radiological assessment. At each prescheduled visit, we also evaluated patient functional status and disease specific and generic health-related quality of life using the mJOA scale, the Nurick score, the Short-Form 36 version 2 (SF-36v2), the neck disability index (NDI), and the 30-m walk test.
Overview of Other Scales The Nurick score is the most commonly cited outcome measure in existing literature. It is a 6-grade ordinal scale that is primarily based on gait impairment and employment (0 = signs or symptoms of root involvement but no evidence of spinal cord disease, V = chair bound or bedridden). It is correlated with the JOA (r = 0.59) and shows high inter- and intra-rater reliability. The Nurick does, however, exhibit low sensitivity (coefficient of variation = 0.33) and poor responsiveness.14 The 30-m walk test requires a patient to stand up from a stable chair, walk on a smooth flat surface for 15 m, turn around, walk back and sit down.6,14 This scale assesses a patient’s voluntary movement, balance and coordinated activity and objectively evaluates walking speed. The 30-m walk test was validated by comparing measurements obtained in a control population with those in patients with myelopathy. Finally, it is sensitive (coefficient of variation for walking time = 0.88), has adequate inter- and intra-rater reliability and can detect change in postoperative gait improvement beyond a patient’s perception. January 2015
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E24
03/12/14 2:23 AM
CERVICAL SPINE
Psychometric Properties of the mJOA Scale • Kopjar et al
The NDI is a 10-item patient questionnaire that addresses functional activities (personal care, lifting, reading, work, driving, sleeping, and recreation), pain intensity, concentration, and headache.15–23 For each item, there are 6 possible answers: 0 is no disability and 5 is complete disability. The total NDI score is out of 100 and is calculated by summating scores from all categories and multiplying by 2. This general health measure is 1-dimensional and has been validated across different patient populations, including both acute and chronic neck pain, and against many functional measures and pain assessment tools. The test-retest reliability is high (>0.90) as well as its internal consistency (α = 0.70–0.90). A downside to this scale is that is exhibits a ceiling effect: it is difficult to detect changes at either extreme end of this scale. The SF-36v2 is a multipurpose health survey, combining a mental component score and physical component score, that measures both functional status and overall quality of life.14,24–26 It consists of 8 scales including physical functioning, role limitations physical pain, bodily pain, general health perceptions, vitality, social functioning, role limitations, emotional health, and mental health. Its validity in patients with CSM is demonstrated by its association with the NDI as well as through confirmation of various constructs. This scale is responsive to change, has adequate test-retest reliability (>0.70, mental component score = 0.88, physical component score = 0.92) and internal consistency (α > 0.85).
Statistical Analysis The following psychometric properties of the mJOA were assessed: internal consistency, dimensionality, validity, and responsiveness to change. To evaluate the internal consistency of the scale, we computed interitem Pearson correlation coefficients and calculated the Cronbach α.27,28 The Cronbach α is a normalized measure of association between multiple components of a scale, with a score of 1 signifying perfect correlation. We also computed a Cronbach α after removing each scale component 1 at a time. Factor analysis was done to determine the dimensionality of the mJOA. We used standard factor analysis and supplemented with Varimax orthogonal rotation to extract factors. Validity refers to how well a scale measures what it intends to measure.29 Given there is no defined “gold standard” for CSM, the criterion validity could not be determined. Instead,
we evaluated convergent construct validity and computed Pearson correlation coefficients for relationships between the mJOA and the Nurick score, NDI, SF-36v2, and 30-m walk test. We also determined association between the 4 components of the mJOA and each of these 4 scales. Divergent construct validity was assessed through correlation analysis with selected dimensions of the SF-36v2 that would be expected to differ from the mJOA. Responsiveness of a scale reflects its ability to detect clinically significant changes over time.30 For the mJOA, this quality is especially important as the scale is often used to measure outcome after surgical intervention. The Cohen effect size was computed by calculating the difference in mean mJOA between baseline and 1 year postoperatively and dividing it by the average standard deviations.
RESULTS All 277 patients enrolled in the CSM-North America study were evaluated preoperatively and comprised the baseline validation sample. There were 165 males and 112 females, with ages in the range from 29 to 88 years (mean, 56.36 ± 11.72 yr). Patients had a wide range of preoperative severity scores (3–18) and a mean baseline mJOA of 12.83 ± 2.72. Two hundred twenty-one patients had a complete 1-year mJOA assessment (80% follow-up rate) and were used to evaluate responsiveness to change. Mean scores at 1 year were in the range from 6 to 18, with a mean of 15.74 ± 2.52.
Internal Consistency The item intercorrelations of a scale are displayed in Table 2. The total mJOA score was highly correlated with both the MDUE (r = 0.802) and MDLE (r = 0.837) extremity components. Sensory dysfunction of the upper extremity and SD were moderately associated with the total mJOA score, with correlation coefficients of 0.598 and 0.524, respectively. With respect to individual scale components, MDUE extremity was moderately correlated with MDLE (r = 0.498) and sensory dysfunction of the upper extremity (r = 0.469). The SD score was weakly associated with the other 3 components of the mJOA. Table 3 displays the Cronbach α for the entire scale and when specific components were excluded. The computed Cronbach α for the mJOA was 0.63. Removal of the MDUE extremity, resulted in the largest drop in Cronbach α to 0.43.
TABLE 2. Pearson Interitem Correlation Coefficients for mJOA (N = 277) mJOA Total Score
Item
Motor Dysfunction Score of the Upper Extremity
Motor Dysfunction Score of the Lower Extremity
Motor dysfunction upper extremity
0.802
Motor dysfunction lower extremity
0.837
0.498
Sensory dysfunction upper extremity
0.598
0.469
0.285
Sphincter dysfunction score
0.524
0.254
0.253
Sensory Dysfunction Score of the Upper Extremity
0.226
mJOA indicates modified Japanese Orthopaedic Association.
Spine
www.spinejournal.com
E25
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E25
03/12/14 2:23 AM
CERVICAL SPINE
Psychometric Properties of the mJOA Scale • Kopjar et al
TABLE 3. Cronbach α for mJOA Total Score
With Excluded Item (N = 277)
Excluded Item
Cronbach α
Motor dysfunction upper extremity
0.43
Motor dysfunction lower extremity
0.56
Sensory dysfunction upper extremity
0.59
Sphincter dysfunction score
0.63
No item excluded
0.63
mJOA indicates modified Japanese Orthopaedic Association.
The exclusion of SD score did not impact the overall Cronbach α; it remained at 0.63.
Dimensionality Factor analysis extracted 2 factors that retained 71% of the initial variance (Table 4). These 2 factors were designated as motor and sensory function of the extremities (factor 1) and SD (factor 2). The factor loadings for factor 1 were all above 0.71: MDUE (0.850) and MDLE (0.716) and sensory dysfunction of the upper extremity (0.745). For factor 2, the factor loadings for SD score was 0.984. No component of the mJOA scale loaded on more than 1 factor.
Validity Table 5 displays Pearson correlation coefficients for the association between the mJOA and the Nurick score, NDI, SF-36v2, and the 30-m walk test. The total mJOA score was moderately associated with the Nurick score (r = −0.625). Low correlation was observed between the mJOA and the NDI (r = −0.343), the physical and mental component score of the SF-36v2 (r = 0.300, r = 0.245, respectively), and the 30-m walk test (r = −0.382). The MDLE score was moderately correlated with the Nurick score (r = −0.68), the SF-36 physical functioning scale (r = 0.490), and the 30-m walk test (r = −0.433). Moderate correlation was also observed between the MDUE score and the Nurick score (r = −0.417). No other components of the mJOA were associated with the other 4 scales. The mJOA showed evidence of divergent validity as it was not correlated with unrelated components of the SF-36v2: bodily pain (r = 0.056), global health perception (r = 0.156), mental health (r = 0.210), emotional role functioning (r = 0.274), social role functioning (r = 0.219), and vitality (r = 0.161).
CSM studies, its psychometric properties have never been determined. This limitation has prevented the adoption of the mJOA as the “gold standard” for assessing baseline severity and postoperative improvements in this patient population. In addition, it is challenging to translate current research efforts into clinical practice if conclusions are based on unvalidated outcome measures. It is therefore the objective of this study to assess, for the first time, the psychometric properties of the mJOA scale. The data used for this study were derived from the prospective CSM-North America study that was originally conducted to determine the efficacy of surgical decompression.13 Quantitative tools are valuable in a clinical setting as they can objectively evaluate severity at baseline, assess the effectiveness of interventions, predict outcome and provide decision support to clinicians. A scale that is used to evaluate a patient’s status and outcome should possess the following qualities: quantifiable, suitably distributed, valid, sensitive, responsive, easy to use, reliable, internally consistent, and clinically relevant. The scale should also address the pathophysiology, key signs and symptoms of the disease, and its natural history. The mJOA evaluates the key signs and symptoms of CSM as it has separate component designated to upper and lower extremity motor function, sensory function of the upper limb and micturition. Because it is out of 18, with 5 and 7 points designated to upper and lower limb motor function, this scale should be able to detect mild functional deficits, making it compatible with the natural history of the disease. The internal consistency of the mJOA was measured by calculating the Cronbach α. If a multi-item assessment tool includes several questions measuring the same factor, then these questions should yield consistent answers. This property attempts to quantify whether items in the same scale measure the same underlying trait. Internal consistency can be a desirable or undesirable quality: a high Cronbach α score indicates reliability and consistency among similar aspects of the scale but may also reflect redundancy. As a general rule of thumb, a Cronbach α value of 0.7 or higher indicates good internal consistency.27,28 In the case of the mJOA, the Cronbach α was a modest 0.63. The underlying trait that the mJOA is attempting to measure is the severity
TABLE 4. Factor Analysis of mJOA Items Item
Factor 1
Factor 2
The baseline mJOA improved from 12.83 ± 2.72 to 15.74 ± 2.52 at 12 months postoperatively (P < 0.001). This change of 2.81 ± 2.81 points translates to a Cohen effect size of 1.
Motor dysfunction upper extremity
0.85061
0.11556
Motor dysfunction lower extremity
0.71579
0.20486
Sensory dysfunction upper extremity
0.74535
0.06704
DISCUSSION
Sphincter dysfunction score
0.15424
0.98387
Responsiveness
The mJOA is an investigator-administered tool used to evaluate functional status in patients with CSM. Although it is one of the most frequently used outcome measures in existing E26
www.spinejournal.com
VariMax rotated factor pattern (N = 277). mJOA indicates modified Japanese Orthopaedic Association. January 2015
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E26
03/12/14 2:23 AM
CERVICAL SPINE
Psychometric Properties of the mJOA Scale • Kopjar et al
TABLE 5. Pearson Correlation Coefficients Between mJOA, mJOA Items and, SF-36v2 Dimensions,
Neck Disability Index, Nurick Score, and Walk Test N
mJOA
Motor Dysfunction Score of the Upper Extremity
Nurick score
277
−0.625
−0.417
−0.680
−0.230
−0.245
NDI
261
−0.343
−0.239
−0.313
−0.227
−0.161
SF-36 physical functioning
262
0.442
0.261
0.490
0.217
0.160
Physical role functioning
262
0.294
0.239
0.306
0.184
0.013
Bodily pain
262
0.056
0.018
0.085
0.071
−0.042
Global health perception
263
0.156
0.135
0.123
0.095
0.078
Mental health
262
0.210
0.167
0.164
0.177
0.091
Emotional role functioning
262
0.274
0.185
0.229
0.192
0.172
Social role functioning
262
0.219
0.205
0.191
0.170
0.020
Vitality
262
0.161
0.131
0.164
0.129
−0.009
SF-36v2 PCS
262
0.300
0.217
0.313
0.189
0.055
SF-36v2 MCS
262
0.245
0.196
0.210
0.193
0.076
Walk test
193
−0.382
−0.213
−0.433
−0.052
−0.229
Variable
Motor Dysfunction Score of the Lower Extremity
Sensory Dysfunction Score of the Upper Extremity
Sphincter Dysfunction Score
NDI indicates Neck Disability Index; PCS, physical component score; MCS, mental component score; mJOA, modified Japanese Orthopaedic Association.
of neurological impairment due to compression of the cervical cord. This modest Cronbach α suggests that the 4 mJOA components evaluate more than 1 trait and the scale is multidimensional. Because the removal of SD did not affect the internal consistency of the scale, we can conclude that this part of the scale measures a different concept. This conclusion was confirmed by factor analysis that determined that the mJOA had 2 key dimensions: the micturition component of the scale was different from the other 3 items. The explanation for this is likely because SD may clinically occur due to several other causes apart from myelopathy. Unfortunately, there is no way to distinguish dysfunction caused by myelopathy versus other conditions. Scales are ideally validated by assessing correlations with a “gold standard.”14,29 Because this has not been defined for CSM, we tested convergent and divergent validity by comparing the mJOA with the Nurick score, SF-36v2, NDI and the 30-m walk test. The mJOA was correlated with the Nurick score, another commonly used measure of assessment of myelopathy severity. This correlation coefficient of −0.625 was higher than a previously reported correlation between the Nurick score and the JOA.14 This is likely because the mJOA has more points designated to lower limb function than the JOA, which is a major component of the Nurick. In addition, the mJOA also showed moderate correlation with the walk test, which is an objective evaluation of a patient’s gait status. Finally, as expected, the lower limb components of the mJOA were moderately correlated with the Nurick, SF-36 physical functioning and the walk test, all tools used Spine
to assess a patient’s physical status with special emphasis on lower limb function. These associations suggest convergent construct validity. On the contrary, the NDI or SF-36 was not associated with the mJOA. The NDI and SF-36 are both based on patient questionnaires and may largely be affected by a patient’s age, ability to cope, general psyche, and by how urgently he thinks he needs surgery. The NDI and SF-36 are highly related due to an overlap of activities and because neck pain likely affects quality of life.15,31 The mJOA, being a measure of functional disability, does not measure the same constructs as quality of life and patient-reported outcome measures. This is confirmed by poor correlation between all components of the SF-36 and the mJOA, suggesting divergent validity. A test that is responsive is extremely valuable as it can detect clinically meaningful change.30 The mJOA is responsive as demonstrated by the difference in mean mJOA at baseline and 12 months and by a Cohen effect size of 1. This statistic reflects that the 2 means differ by 1 standard deviation and that some change in status has occurred. One of the limitations of this study is that we could not evaluate the inter- or intra-rater reliability of the mJOA. In order for the scale to be reliable, it must yield consistent results for repeated uses under the same conditions. Future studies should assess this psychometric property. In addition, if the scale is unreliable then our estimate for responsiveness may not be accurate. www.spinejournal.com
E27
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E27
03/12/14 2:23 AM
CERVICAL SPINE CONCLUSION We report the first detailed analysis of the psychometric properties using data from the prospective CSM-North America study. This scale is multidimensional and measures 2 key components: one that assesses motor and sensory function and the other that evaluates sphincter disturbances. The mJOA demonstrates both convergent and divergent validity and is responsive to change. These results validate existing studies and justify the use of this tool in further research efforts. We hope this study will promote the global standardization of assessment tools and encourage clinicians to use the mJOA, alongside other ancillary measures, to evaluate functional status in patients with CSM.
➢ Key Points This study aims to determine the psychometric properties of the mJOA scale, a widely accepted tool for assessing functional status in patients with CSM. Two hundred seventy-seven surgical patients with CSM were enrolled in the study and evaluated at baseline and at 6, 12, and 24 months postoperatively. The mJOA displayed both convergent and divergent validity based on associations with other scales. The scale’s internal consistency was moderate and the mJOA was responsive to change. The mJOA is a useful tool in the assessment of CSM and should be adopted as the standard for evaluating functional status in this population.
References
1. Kalsi-Ryan S, Karadimas SK, Fehlings MG. Cervical spondylotic myelopathy: the clinical phenomenon and the current pathobiology of an increasingly prevalent and devastating disorder. Neuroscientist 2013;19:409–21. 2. Singh A, Tetreault L, Casey A, et al. A summary of assessment tools for patients suffering from cervical spondylotic myelopathy: a systematic review on validity, reliability, and responsiveness [published online ahead of print September 5, 2013]. Eur Spine J. doi:10.1007/ s00586-013-2935-x. 3. Laing RJ. Measuring outcome in neurosurgery. Br J Neurosurg 2000;14:181–4. 4. Holly LT, Matz PG, Anderson PA, et al. Clinical prognostic indicators of surgical outcome in cervical spondylotic myelopathy. J Neurosurg Spine 2009;11:112–8. 5. Kalsi-Ryan S, Singh A, Massicotte EM, et al. Ancillary outcome measures for assessment of individuals with cervical spondylotic myelopathy. Spine (Phila Pa 1976) 2013;38:S111–22. 6. Singh A, Crockard HA. Quantitative assessment of cervical spondylotic myelopathy by a simple walking test. Lancet 1999;354:370–3. 7. Nurick S. The natural history and the results of surgical treatment of the spinal cord disorder associated with cervical spondylosis. Brain 1972;95:101–8. 8. Olindo S, Signate A, Richech A, et al. Quantitative assessment of hand disability by the nine-hole-peg test (9-HPT) in cervical spondylotic myelopathy. J Neurol Neurosurg Psychiatry 2008;79:965–7.
E28
www.spinejournal.com
Psychometric Properties of the mJOA Scale • Kopjar et al
9. Hosono N, Sakaura H, Mukai Y, et al. A simple performance test for quantifying the severity of cervical myelopathy [erratum in: J Bone Joint Surg Br 2008;90:1534]. J Bone Joint Surg Br 2008;90:1210–3. 10. Casey AT, Bland JM, Crockard HA. Development of a functional scoring system for rheumatoid arthritis patients with cervical myelopathy. Ann Rheum Dis 1996;55:901–6. 11. Benzel EC, Lancon J, Kesterson L, et al. Cervical laminectomy and dentate ligament section for cervical spondylotic myelopathy. J Spinal Disord 1991;4:286–95. 12. Yonenobu K, Abumi K, Nagata K, et al. Interobserver and intraobserver reliability of the Japanese Orthopaedic Association scoring system for evaluation of cervical compression myelopathy. Spine 2001;26:1890–4; discussion 5. 13. Fehlings MG, Wilson JR, Kopjar B, et al. Efficacy and safety of surgical decompression in patients with cervical spondylotic myelopathy: results of the AOSpine North America Prospective Multicenter Study. J Bone Joint Surg Am 2013;95:1651–8. 14. Singh A, Crockard HA. Comparison of seven different scales used to quantify severity of cervical spondylotic myelopathy and postoperative improvement. J Outcome Meas 2001;5:798–818. 15. Pietrobon R, Coeytaux RR, Carey TS, et al. Standard scales for measurement of functional outcome for cervical pain or dysfunction: a systematic review. Spine (Phila Pa 1976) 2002;27:515–22. 16. Cleland JA, Fritz JM, Whitman JM, et al. The reliability and construct validity of the neck disability index and patient specific functional scale in patients with cervical radiculopathy. Spine (Phila Pa 1976) 2006;31:598–602. 17. Hurwitz EL, Morgenstern H, Vassilaki M, et al. Adverse reactions to chiropractic treatment and their effects on satisfaction and clinical outcomes among patients enrolled in the UCLA Neck Pain Study. J Manipulative Physiol Ther 2004;27:16–25. 18. MacDermid JC, Walton DM, Avery S, et al. Measurement properties of the neck disability index: a systematic review. J Orthop Sports Phys Ther 2009;39:400–17. 19. Nederhand MJ, Ijzerman MJ, Hermens HJ, et al. Predictive value of fear avoidance in developing chronic neck pain disability: consequences for clinical decision making. Arch Phys Med Rehabil 2004;85:496–501. 20. Riddle DL, Stratford PW. Use of generic versus region-specific functional status measures on patients with cervical spine disorders. Phys Ther 1998;78:951–63. 21. Vernon H, Mior S. The neck disability index: a study of reliability and validity. J Manipulative Physiol Ther 1991;14:409–15. 22. Young IA, Cleland JA, Michener LA, et al. Reliability, construct validity, and responsiveness of the neck disability index, patientspecific functional scale, and numeric pain rating scale in patients with cervical radiculopathy. Am J Phys Med Rehabil 2010;89:831–9. 23. Bolton JE. Sensitivity and specificity of outcome measures in patients with neck pain: detecting clinically significant improvement. Spine (Phila Pa 1976) 2004;29:2410–7; discussion 8. 24. Holly LT, Matz PG, Anderson PA, et al. Functional outcomes assessment for cervical degenerative disease. J Neurosurg Spine 2009;11:238–44. 25. Kopjar B. The SF-36 health survey: a valid measure of changes in health status after injury. Inj Prev 1996;2:135–9. 26. Brazier JE, Harper R, Jones NM, et al. Validating the SF-36 health survey questionnaire: new outcome measure for primary care. BMJ 1992;305:160–4. 27. Cronbach LJ, Meehl PE. Construct validity in psychological tests. Psychol Bull 1955;52:281–302. 28. Kraemer HC. Extension of the kappa coefficient. Biometrics 1980;36:207–16. 29. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1: 307–10. 30. Deyo RA, Diehr P, Patrick DL. Reproducibility and responsiveness of health status measures. Statistics and strategies for evaluation. Control Clin Trials 1991;12:142S–58S. 31. Latimer M, Haden N, Seeley HM, et al. Measurement of outcome in patients with cervical spondylotic myelopathy treated surgically. Br J Neurosurg 2002;16:545–9. January 2015
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E28
03/12/14 2:23 AM
CERVICAL SPINE
Psychometric Properties of the Modified Japanese Orthopaedic Association Scale in Patients With Cervical Spondylotic Myelopathy Branko Kopjar, MD, PhD, * Lindsay Tetreault, BSc,† Suhkvinder Kalsi-Ryan, PhD,† and Michael Fehlings, MD, PhD†
Study Design. Prospective study. Objective. This study aims to determine the psychometric properties of the modified Japanese Orthopaedic Association (mJOA) scale. Summary of Background Data. Several outcome measures assess functional impairment and quality of life in patients with cervical myelopathy. However, a “gold standard” has not been established. One of the most widely accepted tools for assessing functional status is the mJOA scale. Methods. Two hundred and seventy-seven surgical patients with cervical spondylotic myelopathy were enrolled in the prospective cervical spondylotic myelopathy-North America study. Functional status was evaluated at baseline and at 6, 12, and 24 months postoperatively. The internal consistency of the mJOA was assessed by computing a Cronbach α for the total score and after removing 1 item at a time. Convergent validity and divergent validity were measured by correlating the mJOA with other assessment tools. The responsiveness of the scale was determined by comparing mJOA scores at baseline and 12 months after surgery and computing a Cohen effect size. Results. The internal consistency of the scale was moderate with a Cronbach α of 0.63. Sphincter dysfunction measured a different dimension than the other 3 scale components. The mJOA was correlated with the Nurick score (r = −0.625) but was
From the *Department of Health Services, University of Washington, Seattle, WA; and; †Division of Neurosurgery, Toronto Western Hospital, University of Toronto, University Health Network, Toronto, Ontario, Canada. Acknowledgment date: August 12, 2014. First revision date: September 29, 2014. Acceptance date: October 1, 2014. The manuscript submitted does not contain information about medical device(s)/drug(s). Funds were received from AO Spine for the collection of original data used in this work. Relevant financial activities outside the submitted work: grant, grants pending, consultancy. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivitives 3.0 License, where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially. Address correspondence and reprint requests to Michael G. Fehlings, MD, PhD, Division of Neurosurgery, Toronto Western Hospital, 399 Bathurst St, Ste 4WW-449, Toronto, Ontario M5T2S8, Canada; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000648 Spine
not associated with subscales of the Short-Form 36 that measure different constructs. These findings suggest convergent and divergent validity. The mJOA was responsive to change as reflected by a Cohen effect size of 1. Conclusion. The mJOA is a useful tool in the assessment of cervical spondylotic myelopathy and it should be adopted as the standard for evaluating functional status in this population. Key words: cervical spondylotic myelopathy, CSM, validation, outcome measures, mJOA. Level of Evidence: 3 Spine 2015;40:E23–E28
C
ervical spondylotic myelopathy (CSM) is a progressive degenerative spine disease and the most common cause of spinal cord impairment in adults worldwide.1 The successful management of CSM depends upon an early and accurate diagnosis, an objective assessment of impairment and disability, and an ability to predict outcome. In this field, quantitative measures are increasingly used by clinicians to grade functional and neurological status and to provide decision-making support.2 In addition, objective assessment tools allow clinicians to quantify myelopathy severity, predict outcome, and evaluate surgical benefits by tracking improvements throughout follow-up.3–5 Several outcome measures assess functional impairment and quality of life in patients with cervical myelopathy.6–10 A validated “gold standard,” however, has not been established, preventing the development of quantitative guidelines for CSM management.2 In this field, one of the most widely accepted tool for assessing functional status is the modified Japanese Orthopaedic Association (mJOA) scale.5 This 18-point investigator-administered scale separately addresses motor dysfunction of the upper extremity (MDUE) and motor dysfunction of the lower extremity (MDLE), sensory loss of the upper extremity, and sphincter dysfunction (SD) (Table 1). It was modified from the original Japanese Orthopaedic Association (JOA) scale proposed by Benzel et al11 to increase its applicability in the Western population.11 Some of the differences include that the modified scale has been translated into English and evaluates a patient’s ability to use Western cutlery rather than chopsticks. Although not well defined in the literature, www.spinejournal.com
E23
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E23
03/12/14 2:23 AM
CERVICAL SPINE TABLE 1. The Modified Japanese Orthopaedic
Association Scale
Motor dysfunction score of the upper extremity 0—Inability to move hands 1—Inability to eat with a spoon, but able to move hands
Psychometric Properties of the mJOA Scale • Kopjar et al
from 277 surgical patients with CSM. We anticipate that this work will enable the translation of previous and current research efforts into clinical practice. In addition, if proven both valid and responsive, we recommend that the mJOA be adopted as the standard method for evaluating severity and outcome in patients with CSM.
2—Inability to button shirt, but able to eat with a spoon
MATERIALS AND METHODS
3—Able to button shirt with great difficulty
Subjects
4—Able to button shirt with slight difficulty 5—No dysfunction Motor dysfunction score of the lower extremity 0—Complete loss of motor and sensory function 1—Sensory preservation without ability to move legs 2—Able to move legs, but unable to walk 3—Able to walk on flat floor with a walking aid 4—Able to walk up and/or down stairs with hand rail 5—Moderate-to-significant lack of stability, but able to walk up and/or down stairs without hand rail 6—Mild lack of stability but walks with smooth reciprocation unaided 7—No dysfunction Sensory dysfunction score of the upper extremities 0—Complete loss of hand sensation 1—Severe sensory loss or pain 2—Mild sensory loss 3—No sensory loss Sphincter dysfunction score 0—Inability to micturate voluntarily 1—Marked difficulty with micturation 2—Mild-to-moderate difficulty with micturation 3—Normal micturation
the mJOA seems to be a multidimensional tool that assesses 3 key and distinct components (upper limb dysfunction, lower limb dysfunction, and bladder dysfunction) of CSM. Yonenobu et al12 assessed the reliability of the JOA studying 29 patients with cervical myelopathy secondary to ossification of the posterior longitudinal ligament.12 Both the inter- and intraobserver reliabilities were high (0.81 and 0.84, respectively), indicating that the JOA scale is a reasonable and valuable tool for the assessment of patients with cervical myelopathy. Because the differences between the JOA and mJOA are substantial, it cannot be assumed that the mJOA carries the same psychometric properties. Despite its widespread use, this instrument has never been subjected to rigorous evaluation of reliability, responsiveness, and validity. This study aims to assess the internal consistency, dimensionality, validity, and responsiveness of the mJOA using data E24
www.spinejournal.com
Between December 2005 and September 2007, 277 patients were enrolled in the prospective multicenter AOSpine CSMNorth America study at 12 North American centers.13 Patients were asked to participate in this study if they were referred to a site’s orthopedic or neurosurgery department and if they met the following inclusion criteria: (1) aged 18 years or older; (2) presenting with symptomatic CSM with at least 1 clinical sign of myelopathy; (3) evidence of objective cervical cord compression on a magnetic resonance image; (4) no previous surgical treatment for myelopathy; and (5) absence of lumbar stenosis. Patients were not excluded on the basis of duration of symptoms, myelopathy severity, or prior conservative treatment. All patients received anterior or posterior decompression and reconstruction at their respective sites. The surgical approach, the number of operated segments, and whether or not to use instrumentation varied case by case and was determined by the attending surgeon. Postoperative rehabilitation was per standard of care at the treating institutions. Extensive data for each participating subject were collected at baseline, 6, 12, and 24 months, including demographic information, surgical summary, symptomatology, medical history, and radiological assessment. At each prescheduled visit, we also evaluated patient functional status and disease specific and generic health-related quality of life using the mJOA scale, the Nurick score, the Short-Form 36 version 2 (SF-36v2), the neck disability index (NDI), and the 30-m walk test.
Overview of Other Scales The Nurick score is the most commonly cited outcome measure in existing literature. It is a 6-grade ordinal scale that is primarily based on gait impairment and employment (0 = signs or symptoms of root involvement but no evidence of spinal cord disease, V = chair bound or bedridden). It is correlated with the JOA (r = 0.59) and shows high inter- and intra-rater reliability. The Nurick does, however, exhibit low sensitivity (coefficient of variation = 0.33) and poor responsiveness.14 The 30-m walk test requires a patient to stand up from a stable chair, walk on a smooth flat surface for 15 m, turn around, walk back and sit down.6,14 This scale assesses a patient’s voluntary movement, balance and coordinated activity and objectively evaluates walking speed. The 30-m walk test was validated by comparing measurements obtained in a control population with those in patients with myelopathy. Finally, it is sensitive (coefficient of variation for walking time = 0.88), has adequate inter- and intra-rater reliability and can detect change in postoperative gait improvement beyond a patient’s perception. January 2015
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E24
03/12/14 2:23 AM
CERVICAL SPINE
Psychometric Properties of the mJOA Scale • Kopjar et al
The NDI is a 10-item patient questionnaire that addresses functional activities (personal care, lifting, reading, work, driving, sleeping, and recreation), pain intensity, concentration, and headache.15–23 For each item, there are 6 possible answers: 0 is no disability and 5 is complete disability. The total NDI score is out of 100 and is calculated by summating scores from all categories and multiplying by 2. This general health measure is 1-dimensional and has been validated across different patient populations, including both acute and chronic neck pain, and against many functional measures and pain assessment tools. The test-retest reliability is high (>0.90) as well as its internal consistency (α = 0.70–0.90). A downside to this scale is that is exhibits a ceiling effect: it is difficult to detect changes at either extreme end of this scale. The SF-36v2 is a multipurpose health survey, combining a mental component score and physical component score, that measures both functional status and overall quality of life.14,24–26 It consists of 8 scales including physical functioning, role limitations physical pain, bodily pain, general health perceptions, vitality, social functioning, role limitations, emotional health, and mental health. Its validity in patients with CSM is demonstrated by its association with the NDI as well as through confirmation of various constructs. This scale is responsive to change, has adequate test-retest reliability (>0.70, mental component score = 0.88, physical component score = 0.92) and internal consistency (α > 0.85).
Statistical Analysis The following psychometric properties of the mJOA were assessed: internal consistency, dimensionality, validity, and responsiveness to change. To evaluate the internal consistency of the scale, we computed interitem Pearson correlation coefficients and calculated the Cronbach α.27,28 The Cronbach α is a normalized measure of association between multiple components of a scale, with a score of 1 signifying perfect correlation. We also computed a Cronbach α after removing each scale component 1 at a time. Factor analysis was done to determine the dimensionality of the mJOA. We used standard factor analysis and supplemented with Varimax orthogonal rotation to extract factors. Validity refers to how well a scale measures what it intends to measure.29 Given there is no defined “gold standard” for CSM, the criterion validity could not be determined. Instead,
we evaluated convergent construct validity and computed Pearson correlation coefficients for relationships between the mJOA and the Nurick score, NDI, SF-36v2, and 30-m walk test. We also determined association between the 4 components of the mJOA and each of these 4 scales. Divergent construct validity was assessed through correlation analysis with selected dimensions of the SF-36v2 that would be expected to differ from the mJOA. Responsiveness of a scale reflects its ability to detect clinically significant changes over time.30 For the mJOA, this quality is especially important as the scale is often used to measure outcome after surgical intervention. The Cohen effect size was computed by calculating the difference in mean mJOA between baseline and 1 year postoperatively and dividing it by the average standard deviations.
RESULTS All 277 patients enrolled in the CSM-North America study were evaluated preoperatively and comprised the baseline validation sample. There were 165 males and 112 females, with ages in the range from 29 to 88 years (mean, 56.36 ± 11.72 yr). Patients had a wide range of preoperative severity scores (3–18) and a mean baseline mJOA of 12.83 ± 2.72. Two hundred twenty-one patients had a complete 1-year mJOA assessment (80% follow-up rate) and were used to evaluate responsiveness to change. Mean scores at 1 year were in the range from 6 to 18, with a mean of 15.74 ± 2.52.
Internal Consistency The item intercorrelations of a scale are displayed in Table 2. The total mJOA score was highly correlated with both the MDUE (r = 0.802) and MDLE (r = 0.837) extremity components. Sensory dysfunction of the upper extremity and SD were moderately associated with the total mJOA score, with correlation coefficients of 0.598 and 0.524, respectively. With respect to individual scale components, MDUE extremity was moderately correlated with MDLE (r = 0.498) and sensory dysfunction of the upper extremity (r = 0.469). The SD score was weakly associated with the other 3 components of the mJOA. Table 3 displays the Cronbach α for the entire scale and when specific components were excluded. The computed Cronbach α for the mJOA was 0.63. Removal of the MDUE extremity, resulted in the largest drop in Cronbach α to 0.43.
TABLE 2. Pearson Interitem Correlation Coefficients for mJOA (N = 277) mJOA Total Score
Item
Motor Dysfunction Score of the Upper Extremity
Motor Dysfunction Score of the Lower Extremity
Motor dysfunction upper extremity
0.802
Motor dysfunction lower extremity
0.837
0.498
Sensory dysfunction upper extremity
0.598
0.469
0.285
Sphincter dysfunction score
0.524
0.254
0.253
Sensory Dysfunction Score of the Upper Extremity
0.226
mJOA indicates modified Japanese Orthopaedic Association.
Spine
www.spinejournal.com
E25
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E25
03/12/14 2:23 AM
CERVICAL SPINE
Psychometric Properties of the mJOA Scale • Kopjar et al
TABLE 3. Cronbach α for mJOA Total Score
With Excluded Item (N = 277)
Excluded Item
Cronbach α
Motor dysfunction upper extremity
0.43
Motor dysfunction lower extremity
0.56
Sensory dysfunction upper extremity
0.59
Sphincter dysfunction score
0.63
No item excluded
0.63
mJOA indicates modified Japanese Orthopaedic Association.
The exclusion of SD score did not impact the overall Cronbach α; it remained at 0.63.
Dimensionality Factor analysis extracted 2 factors that retained 71% of the initial variance (Table 4). These 2 factors were designated as motor and sensory function of the extremities (factor 1) and SD (factor 2). The factor loadings for factor 1 were all above 0.71: MDUE (0.850) and MDLE (0.716) and sensory dysfunction of the upper extremity (0.745). For factor 2, the factor loadings for SD score was 0.984. No component of the mJOA scale loaded on more than 1 factor.
Validity Table 5 displays Pearson correlation coefficients for the association between the mJOA and the Nurick score, NDI, SF-36v2, and the 30-m walk test. The total mJOA score was moderately associated with the Nurick score (r = −0.625). Low correlation was observed between the mJOA and the NDI (r = −0.343), the physical and mental component score of the SF-36v2 (r = 0.300, r = 0.245, respectively), and the 30-m walk test (r = −0.382). The MDLE score was moderately correlated with the Nurick score (r = −0.68), the SF-36 physical functioning scale (r = 0.490), and the 30-m walk test (r = −0.433). Moderate correlation was also observed between the MDUE score and the Nurick score (r = −0.417). No other components of the mJOA were associated with the other 4 scales. The mJOA showed evidence of divergent validity as it was not correlated with unrelated components of the SF-36v2: bodily pain (r = 0.056), global health perception (r = 0.156), mental health (r = 0.210), emotional role functioning (r = 0.274), social role functioning (r = 0.219), and vitality (r = 0.161).
CSM studies, its psychometric properties have never been determined. This limitation has prevented the adoption of the mJOA as the “gold standard” for assessing baseline severity and postoperative improvements in this patient population. In addition, it is challenging to translate current research efforts into clinical practice if conclusions are based on unvalidated outcome measures. It is therefore the objective of this study to assess, for the first time, the psychometric properties of the mJOA scale. The data used for this study were derived from the prospective CSM-North America study that was originally conducted to determine the efficacy of surgical decompression.13 Quantitative tools are valuable in a clinical setting as they can objectively evaluate severity at baseline, assess the effectiveness of interventions, predict outcome and provide decision support to clinicians. A scale that is used to evaluate a patient’s status and outcome should possess the following qualities: quantifiable, suitably distributed, valid, sensitive, responsive, easy to use, reliable, internally consistent, and clinically relevant. The scale should also address the pathophysiology, key signs and symptoms of the disease, and its natural history. The mJOA evaluates the key signs and symptoms of CSM as it has separate component designated to upper and lower extremity motor function, sensory function of the upper limb and micturition. Because it is out of 18, with 5 and 7 points designated to upper and lower limb motor function, this scale should be able to detect mild functional deficits, making it compatible with the natural history of the disease. The internal consistency of the mJOA was measured by calculating the Cronbach α. If a multi-item assessment tool includes several questions measuring the same factor, then these questions should yield consistent answers. This property attempts to quantify whether items in the same scale measure the same underlying trait. Internal consistency can be a desirable or undesirable quality: a high Cronbach α score indicates reliability and consistency among similar aspects of the scale but may also reflect redundancy. As a general rule of thumb, a Cronbach α value of 0.7 or higher indicates good internal consistency.27,28 In the case of the mJOA, the Cronbach α was a modest 0.63. The underlying trait that the mJOA is attempting to measure is the severity
TABLE 4. Factor Analysis of mJOA Items Item
Factor 1
Factor 2
The baseline mJOA improved from 12.83 ± 2.72 to 15.74 ± 2.52 at 12 months postoperatively (P < 0.001). This change of 2.81 ± 2.81 points translates to a Cohen effect size of 1.
Motor dysfunction upper extremity
0.85061
0.11556
Motor dysfunction lower extremity
0.71579
0.20486
Sensory dysfunction upper extremity
0.74535
0.06704
DISCUSSION
Sphincter dysfunction score
0.15424
0.98387
Responsiveness
The mJOA is an investigator-administered tool used to evaluate functional status in patients with CSM. Although it is one of the most frequently used outcome measures in existing E26
www.spinejournal.com
VariMax rotated factor pattern (N = 277). mJOA indicates modified Japanese Orthopaedic Association. January 2015
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E26
03/12/14 2:23 AM
CERVICAL SPINE
Psychometric Properties of the mJOA Scale • Kopjar et al
TABLE 5. Pearson Correlation Coefficients Between mJOA, mJOA Items and, SF-36v2 Dimensions,
Neck Disability Index, Nurick Score, and Walk Test N
mJOA
Motor Dysfunction Score of the Upper Extremity
Nurick score
277
−0.625
−0.417
−0.680
−0.230
−0.245
NDI
261
−0.343
−0.239
−0.313
−0.227
−0.161
SF-36 physical functioning
262
0.442
0.261
0.490
0.217
0.160
Physical role functioning
262
0.294
0.239
0.306
0.184
0.013
Bodily pain
262
0.056
0.018
0.085
0.071
−0.042
Global health perception
263
0.156
0.135
0.123
0.095
0.078
Mental health
262
0.210
0.167
0.164
0.177
0.091
Emotional role functioning
262
0.274
0.185
0.229
0.192
0.172
Social role functioning
262
0.219
0.205
0.191
0.170
0.020
Vitality
262
0.161
0.131
0.164
0.129
−0.009
SF-36v2 PCS
262
0.300
0.217
0.313
0.189
0.055
SF-36v2 MCS
262
0.245
0.196
0.210
0.193
0.076
Walk test
193
−0.382
−0.213
−0.433
−0.052
−0.229
Variable
Motor Dysfunction Score of the Lower Extremity
Sensory Dysfunction Score of the Upper Extremity
Sphincter Dysfunction Score
NDI indicates Neck Disability Index; PCS, physical component score; MCS, mental component score; mJOA, modified Japanese Orthopaedic Association.
of neurological impairment due to compression of the cervical cord. This modest Cronbach α suggests that the 4 mJOA components evaluate more than 1 trait and the scale is multidimensional. Because the removal of SD did not affect the internal consistency of the scale, we can conclude that this part of the scale measures a different concept. This conclusion was confirmed by factor analysis that determined that the mJOA had 2 key dimensions: the micturition component of the scale was different from the other 3 items. The explanation for this is likely because SD may clinically occur due to several other causes apart from myelopathy. Unfortunately, there is no way to distinguish dysfunction caused by myelopathy versus other conditions. Scales are ideally validated by assessing correlations with a “gold standard.”14,29 Because this has not been defined for CSM, we tested convergent and divergent validity by comparing the mJOA with the Nurick score, SF-36v2, NDI and the 30-m walk test. The mJOA was correlated with the Nurick score, another commonly used measure of assessment of myelopathy severity. This correlation coefficient of −0.625 was higher than a previously reported correlation between the Nurick score and the JOA.14 This is likely because the mJOA has more points designated to lower limb function than the JOA, which is a major component of the Nurick. In addition, the mJOA also showed moderate correlation with the walk test, which is an objective evaluation of a patient’s gait status. Finally, as expected, the lower limb components of the mJOA were moderately correlated with the Nurick, SF-36 physical functioning and the walk test, all tools used Spine
to assess a patient’s physical status with special emphasis on lower limb function. These associations suggest convergent construct validity. On the contrary, the NDI or SF-36 was not associated with the mJOA. The NDI and SF-36 are both based on patient questionnaires and may largely be affected by a patient’s age, ability to cope, general psyche, and by how urgently he thinks he needs surgery. The NDI and SF-36 are highly related due to an overlap of activities and because neck pain likely affects quality of life.15,31 The mJOA, being a measure of functional disability, does not measure the same constructs as quality of life and patient-reported outcome measures. This is confirmed by poor correlation between all components of the SF-36 and the mJOA, suggesting divergent validity. A test that is responsive is extremely valuable as it can detect clinically meaningful change.30 The mJOA is responsive as demonstrated by the difference in mean mJOA at baseline and 12 months and by a Cohen effect size of 1. This statistic reflects that the 2 means differ by 1 standard deviation and that some change in status has occurred. One of the limitations of this study is that we could not evaluate the inter- or intra-rater reliability of the mJOA. In order for the scale to be reliable, it must yield consistent results for repeated uses under the same conditions. Future studies should assess this psychometric property. In addition, if the scale is unreliable then our estimate for responsiveness may not be accurate. www.spinejournal.com
E27
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E27
03/12/14 2:23 AM
CERVICAL SPINE CONCLUSION We report the first detailed analysis of the psychometric properties using data from the prospective CSM-North America study. This scale is multidimensional and measures 2 key components: one that assesses motor and sensory function and the other that evaluates sphincter disturbances. The mJOA demonstrates both convergent and divergent validity and is responsive to change. These results validate existing studies and justify the use of this tool in further research efforts. We hope this study will promote the global standardization of assessment tools and encourage clinicians to use the mJOA, alongside other ancillary measures, to evaluate functional status in patients with CSM.
➢ Key Points This study aims to determine the psychometric properties of the mJOA scale, a widely accepted tool for assessing functional status in patients with CSM. Two hundred seventy-seven surgical patients with CSM were enrolled in the study and evaluated at baseline and at 6, 12, and 24 months postoperatively. The mJOA displayed both convergent and divergent validity based on associations with other scales. The scale’s internal consistency was moderate and the mJOA was responsive to change. The mJOA is a useful tool in the assessment of CSM and should be adopted as the standard for evaluating functional status in this population.
References
1. Kalsi-Ryan S, Karadimas SK, Fehlings MG. Cervical spondylotic myelopathy: the clinical phenomenon and the current pathobiology of an increasingly prevalent and devastating disorder. Neuroscientist 2013;19:409–21. 2. Singh A, Tetreault L, Casey A, et al. A summary of assessment tools for patients suffering from cervical spondylotic myelopathy: a systematic review on validity, reliability, and responsiveness [published online ahead of print September 5, 2013]. Eur Spine J. doi:10.1007/ s00586-013-2935-x. 3. Laing RJ. Measuring outcome in neurosurgery. Br J Neurosurg 2000;14:181–4. 4. Holly LT, Matz PG, Anderson PA, et al. Clinical prognostic indicators of surgical outcome in cervical spondylotic myelopathy. J Neurosurg Spine 2009;11:112–8. 5. Kalsi-Ryan S, Singh A, Massicotte EM, et al. Ancillary outcome measures for assessment of individuals with cervical spondylotic myelopathy. Spine (Phila Pa 1976) 2013;38:S111–22. 6. Singh A, Crockard HA. Quantitative assessment of cervical spondylotic myelopathy by a simple walking test. Lancet 1999;354:370–3. 7. Nurick S. The natural history and the results of surgical treatment of the spinal cord disorder associated with cervical spondylosis. Brain 1972;95:101–8. 8. Olindo S, Signate A, Richech A, et al. Quantitative assessment of hand disability by the nine-hole-peg test (9-HPT) in cervical spondylotic myelopathy. J Neurol Neurosurg Psychiatry 2008;79:965–7.
E28
www.spinejournal.com
Psychometric Properties of the mJOA Scale • Kopjar et al
9. Hosono N, Sakaura H, Mukai Y, et al. A simple performance test for quantifying the severity of cervical myelopathy [erratum in: J Bone Joint Surg Br 2008;90:1534]. J Bone Joint Surg Br 2008;90:1210–3. 10. Casey AT, Bland JM, Crockard HA. Development of a functional scoring system for rheumatoid arthritis patients with cervical myelopathy. Ann Rheum Dis 1996;55:901–6. 11. Benzel EC, Lancon J, Kesterson L, et al. Cervical laminectomy and dentate ligament section for cervical spondylotic myelopathy. J Spinal Disord 1991;4:286–95. 12. Yonenobu K, Abumi K, Nagata K, et al. Interobserver and intraobserver reliability of the Japanese Orthopaedic Association scoring system for evaluation of cervical compression myelopathy. Spine 2001;26:1890–4; discussion 5. 13. Fehlings MG, Wilson JR, Kopjar B, et al. Efficacy and safety of surgical decompression in patients with cervical spondylotic myelopathy: results of the AOSpine North America Prospective Multicenter Study. J Bone Joint Surg Am 2013;95:1651–8. 14. Singh A, Crockard HA. Comparison of seven different scales used to quantify severity of cervical spondylotic myelopathy and postoperative improvement. J Outcome Meas 2001;5:798–818. 15. Pietrobon R, Coeytaux RR, Carey TS, et al. Standard scales for measurement of functional outcome for cervical pain or dysfunction: a systematic review. Spine (Phila Pa 1976) 2002;27:515–22. 16. Cleland JA, Fritz JM, Whitman JM, et al. The reliability and construct validity of the neck disability index and patient specific functional scale in patients with cervical radiculopathy. Spine (Phila Pa 1976) 2006;31:598–602. 17. Hurwitz EL, Morgenstern H, Vassilaki M, et al. Adverse reactions to chiropractic treatment and their effects on satisfaction and clinical outcomes among patients enrolled in the UCLA Neck Pain Study. J Manipulative Physiol Ther 2004;27:16–25. 18. MacDermid JC, Walton DM, Avery S, et al. Measurement properties of the neck disability index: a systematic review. J Orthop Sports Phys Ther 2009;39:400–17. 19. Nederhand MJ, Ijzerman MJ, Hermens HJ, et al. Predictive value of fear avoidance in developing chronic neck pain disability: consequences for clinical decision making. Arch Phys Med Rehabil 2004;85:496–501. 20. Riddle DL, Stratford PW. Use of generic versus region-specific functional status measures on patients with cervical spine disorders. Phys Ther 1998;78:951–63. 21. Vernon H, Mior S. The neck disability index: a study of reliability and validity. J Manipulative Physiol Ther 1991;14:409–15. 22. Young IA, Cleland JA, Michener LA, et al. Reliability, construct validity, and responsiveness of the neck disability index, patientspecific functional scale, and numeric pain rating scale in patients with cervical radiculopathy. Am J Phys Med Rehabil 2010;89:831–9. 23. Bolton JE. Sensitivity and specificity of outcome measures in patients with neck pain: detecting clinically significant improvement. Spine (Phila Pa 1976) 2004;29:2410–7; discussion 8. 24. Holly LT, Matz PG, Anderson PA, et al. Functional outcomes assessment for cervical degenerative disease. J Neurosurg Spine 2009;11:238–44. 25. Kopjar B. The SF-36 health survey: a valid measure of changes in health status after injury. Inj Prev 1996;2:135–9. 26. Brazier JE, Harper R, Jones NM, et al. Validating the SF-36 health survey questionnaire: new outcome measure for primary care. BMJ 1992;305:160–4. 27. Cronbach LJ, Meehl PE. Construct validity in psychological tests. Psychol Bull 1955;52:281–302. 28. Kraemer HC. Extension of the kappa coefficient. Biometrics 1980;36:207–16. 29. Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1986;1: 307–10. 30. Deyo RA, Diehr P, Patrick DL. Reproducibility and responsiveness of health status measures. Statistics and strategies for evaluation. Control Clin Trials 1991;12:142S–58S. 31. Latimer M, Haden N, Seeley HM, et al. Measurement of outcome in patients with cervical spondylotic myelopathy treated surgically. Br J Neurosurg 2002;16:545–9. January 2015
Copyright © 2014 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. SPINE141067_LR E28
03/12/14 2:23 AM
