Novel Method Using Baseline Normalization and Area Under the Curve to Evaluate Differences in Outcome Between Treatment Groups and Application to Patients With Cervical Spondylotic Myelopathy Undergoing Anterior Versus Posterior Surgery

STUDY DESIGN.:Retrospective review of a prospective database. OBJECTIVE.:To describe a novel method that uses baseline normalization and area under the curve (AUC) to compare surgical outcomes between patients surgically treated anteriorly versus posteriorly for cervical spondylotic myelopathy (CSM). SUMMARY AND BACKGROUND DATA.:It is important to control for baseline characteristics, especially disease severity, when evaluating differences in outcomes between 2 treatment groups. However, current methods of reporting outcomes are limited perhaps diminish the health impact of the entire postoperative recovery experience. METHODS.:In the prospective, multicenter AO Spine North America CSM database, 147 patients had complete modified Japanese Orthopaedic Association (mJOA) data at baseline and at 6-, 12-, and 24-months postoperatively and were either treated anteriorly (n = 94) or posteriorly (n = 53). Each patientʼs follow-up mJOA scores were normalized by dividing them by the patientʼs baseline value. A graph was then plotted with the time point on the x-axis and the normalized score or “recovery index” on the y-axis. The AUC was calculated and then compared between the anterior and posterior surgical approach groups. RESULTS.:The non-normalized recovery profile of the anterior group was better than that of the posterior group, as the patients treated anteriorly had less functional impairment at baseline. After normalization, patients in the anterior and posterior group had similar recovery indices and AUCs at 6-months following surgery. At 24-months, patients treated posteriorly had a significantly higher recovery index (1.32) and a larger AUC (16.3) than those treated anteriorly (1.11, 14.5, P = 0.004 and P = 0.006, respectively). CONCLUSION.:This is the first study to apply AUC analysis to patients with CSM. In surgical patients with CSM, those treated anteriorly achieved a higher mJOA score at all time points than those treated posteriorly. The recovery indices, however, were not significantly different between approach groups at 6 months.Level of Evidence3