Proximal and distal reciprocal changes following cervical deformity malalignment correction

OBJECTIVE Hyperextension of C0-2 is a debilitating compensatory mechanism used to maintain horizontal gaze, analogous to high pelvic tilt in the lumbopelvic complex to maintain an upright posture. This study aims to investigate the impact of cervical deformity (CD) correction on this hyperextension. The authors hypothesize that correction of cervical sagittal malalignment allows for relaxation of C0-2 hyperextension and improved clinical outcomes. METHODS A retrospective review was conducted of a multicenter database of patients with CD undergoing spinal realignment and fusion caudal to C2 and cephalad to the pelvis. Range of motion (ROM) and reserve of extension (ROE) were calculated across C2-7 and C0-2. The association between C2-7 correction and change in C0-2 ROE was inves-tigated while controlling for horizontal gaze, followed by stratification into Delta C2-7 percentiles. RESULTS Sixty-five patients were included (mean age 61.8 +/- 9.6 years, 68% female). At baseline, patients had cervical kyphosis (C2-7, -11.7 degrees +/- 18.2 degrees; T1 slope-cervical lordosis mismatch, 38.6 degrees +/- 18.6 degrees), negative global alignment (sagittal vertical axis [SVA] -12.8 +/- 71.2 mm), and hyperlordosis at C0-2 (mean 33.2 degrees +/- 11.8 degrees). The mean ROM was 25.7 degrees +/- 17.7 degrees and 21.3 degrees +/- 9.9 degrees at C2-7 and C0-2, respectively, with an ROE of approximately 9 degrees for each segment. Limited C0-2 ROM and ROE correlated with the Neck Disability Index (r = -0.371 and -0.394, p < 0.01). The mean number of levels fused was 7.0 +/- 3.1 (24.6% anterior, 43.1% posterior), with 87.7% undergoing at least an osteotomy. At 1 year, mean C2-7 increased to 5.5 degrees +/- 13.4 degrees, SVA became neutral (11.5 +/- 54.8 mm), C0-2 hyperlordosis decreased to 27.8 degrees +/- 11.7 degrees, and thoracic kyphosis (TK) increased to -49.4 degrees +/- 18.1 degrees (all p < 0.001). Concurrently, mean C0-2 ROM increased to 27.6 degrees +/- 8.1 degrees and C2-7 ROM decreased significantly to 9.0 degrees +/- 12.3 degrees without a change in ROE. Controlling for horizon-tal gaze, change in C2-7 lordosis significantly correlated with increased TK (r = -0.617, p < 0.001), decreased C0-2 (r = -0.747, p < 0.001), and increased C0-2 ROE (r = 0.550, p = 0.002). CONCLUSIONS CD correction can significantly impact cephalad and caudal compensation in the upper cervical and thoracic spine. Restoration of cervical alignment resulted in increased C0-2 ROE and TK and was also associated with improved clinical outcome.