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Minimum clinically important differences in the Cervical Spine Outcomes Questionnaire: results from a national multicenter study of patients treated with anterior cervical decompression and arthrodesis.

BACKGROUND
The minimum clinically important difference is a clinically relevant threshold of improvement. A substantial clinical benefit is a threshold of change that correlates with clinically important improvement. The Cervical Spine Outcomes Questionnaire is a disease-specific, patient-reported outcomes instrument that was developed to be sensitive to changes associated with surgical treatment for degenerative cervical disc disease. To determine thresholds for change in these domain scores that are important from the patient's perspective, we estimated the minimum clinically important difference and substantial clinical benefit values for this questionnaire's domain scores.


METHODS
We evaluated 252 patients from the Cervical Spine Research Society Outcomes Study at their six-month follow-up visits after anterior cervical spine decompression and arthrodesis. Using a receiver operating characteristics curve, with the health transition item of the Short Form-36 as an anchor, we determined that the minimum clinically important difference (the value that maximized sensitivity and specificity to differentiate the "somewhat better" and "much better" responses from others) and the substantial clinical benefit (the value that maximized sensitivity and specificity to differentiate the "much better" response from others) for our questionnaire's domain scores. Responses were scaled between 0 and 1 point; higher scores denoted more severe impairment. Patient and clinical characteristics were tested to determine their influence on score changes.


RESULTS
The minimum clinically important difference ranged from 0.13 point (for functional disability) to 0.24 point (for arm/shoulder pain). The substantial clinical benefit score ranged from 0.20 point (for functional disability or physical symptoms other than pain) to 0.30 point (for neck or arm/shoulder pain). Age, sex, and duration of current symptoms were not associated with change in our questionnaire's domain scores.


CONCLUSIONS
A 0.13-point change in the functional disability domain score indicated a clinically important difference in a self-reported outcome after anterior cervical spine surgery. A 0.30-point change in neck pain after surgery indicated a clinically important clinical benefit. This information, coupled with previous reports of the psychometric stability of the Cervical Spine Outcomes Questionnaire, should increase the clinical utility of this patient-reported outcomes instrument.