Criteria for success after surgery for cervical radiculopathy—estimates for a substantial amount of improvement in core outcome measures

Background context: Defining clinically meaningful success criteria from patient-reported outcome measures (PROMs) is crucial for clinical audits, research and decision-making. Purpose: We aimed to define criteria for a successful outcome 3 and 12 months after surgery for cervical degenerative radiculopathy on recommended PROMs. Study design: Prospective cohort study with 12 months follow-up. Patient sample: Patients operated at one or two levels for cervical radiculopathy included in the Norwegian Registry for Spine Surgery (NORspine) from 2011 to 2016. Outcome measures: Neck disability index (NDI), Numeric Rating Scale for neck pain (NRS-NP) and arm pain (NRS-AP), health-related quality-of-life EuroQol 3L (EQ-5D), general health status (EQ-VAS). Methods: We included 2,868 consecutive cervical degenerative radiculopathy patients operated for cervical radiculopathy in one or two levels and included in the Norwegian Registry for Spine Surgery (NORspine). External criterion to determine accuracy and optimal cut-off values for success in the PROMs was the global perceived effect scale. Success was defined as “much better” or “completely recovered.” Cut-off values were assessed by analyzing the area under the receiver operating curves for follow-up scores, mean change scores, and percentage change scores. Results: All PROMs showed high accuracy in defining success and nonsuccess and only minor differences were found between 3- and 12-month scores. At 12 months, the area under the receiver operating curves for follow-up scores were 0.86 to 0.91, change scores were 0.74 to 0.87, and percentage change scores were 0.74 to 0.91. Percentage scores of NDI and NRS-AP showed the best accuracy. The optimal cut-off values for each PROM showed considerable overlap across those operated due to disc herniation and spondylotic foraminal stenosis. Conclusions: All PROMs, especially NDI and NRS-AP, showed good to excellent discriminative ability in distinguishing between a successful and nonsuccessful outcome after surgery due to cervical radiculopathy. Percentage change scores are recommended for use in research and clinical practice