Determining the time frame of maximum clinical improvement in surgical decompression for cervical spondylotic myelopathy when stratified by preoperative myelopathy severity: a cervical Quality Outcomes Database study
Authors: Berlin Connor , Marino Alexandria C. , Mummaneni Praveen V. , Uribe Juan , Tumialán Luis M. , Turner Jay , Wang Michael Y. , Park Paul , Bisson Erica F. , Shaffrey Mark , Gottfried Oren , Than Khoi D. , Fu Kai-Ming , Foley Kevin , Chan Andrew K. , Bydon Mohamad , Alvi Mohammed Ali , Upadhyaya Cheerag , Coric Domagoj , Asher Anthony , Potts Eric A. , Knightly John , Meyer Scott , Buchholz Avery 
Published: June 2022

OBJECTIVE
While surgical decompression is an important treatment modality for cervical spondylotic myelopathy (CSM), it remains unclear if the severity of preoperative myelopathy status affects potential benefit from surgical intervention and when maximum postoperative improvement is expected. This investigation sought to determine if retrospective analysis of prospectively collected patient-reported outcomes (PROs) following surgery for CSM differed when stratified by preoperative myelopathy status. Secondary objectives included assessment of the minimal clinically important difference (MCID).

METHODS
A total of 1151 patients with CSM were prospectively enrolled from the Quality Outcomes Database at 14 US hospitals. Baseline demographics and PROs at baseline and 3 and 12 months were measured. These included the modified Japanese Orthopaedic Association (mJOA) score, Neck Disability Index (NDI), quality-adjusted life-years (QALYs) from the EQ-5D, and visual analog scale from the EQ-5D (EQ-VAS). Patients were stratified by preoperative myelopathy severity using criteria established by the AO Spine study group: mild (mJOA score 15–17), moderate (mJOA score 12–14), or severe (mJOA score < 12). Univariate analysis was used to identify demographic variables that significantly varied between myelopathy groups. Then, multivariate linear regression and linear mixed regression were used to model the effect of severity and time on PROs, respectively.

RESULTS
For NDI, EQ-VAS, and QALY, patients in all myelopathy cohorts achieved significant, maximal improvement at 3 months without further improvement at 12 months. For mJOA, moderate and severe myelopathy groups demonstrated significant, maximal improvement at 3 months, without further improvement at 12 months. The mild myelopathy group did not demonstrate significant change in mJOA score but did maintain and achieve higher PRO scores overall when compared with more advanced myelopathy cohorts. The MCID threshold was reached in all myelopathy cohorts at 3 months for mJOA, NDI, EQ-VAS, and QALY, with the only exception being mild myelopathy QALY at 3 months.

CONCLUSIONS
As assessed by statistical regression and MCID analysis, patients with cervical myelopathy experience maximal improvement in their quality of life, neck disability, myelopathy score, and overall health by 3 months after surgical decompression, regardless of their baseline myelopathy severity. An exception was seen for the mJOA score in the mild myelopathy cohort, improvement of which may have been limited by ceiling effect. The data presented here will aid surgeons in patient selection, preoperative counseling, and expected postoperative time courses.