126. Proximal and distal reciprocal alignment changes following cervical deformity correction

Abstract

<h3>BACKGROUND CONTEXT</h3> Hyperextension of C0-C2 is a painful compensatory mechanism used to maintain horizontal gaze that is analogous to high pelvic tilt to maintain upright posture. The magnitude and impact of relaxation of this hyperextension following CD correction are not well understood. <h3>PURPOSE</h3> To investigate whether correction of cervical sagittal malalignment allows for relaxation of C0–C2 hyperextension and improved clinical outcome. <h3>STUDY DESIGN/SETTING</h3> Retrospective review. <h3>PATIENT SAMPLE</h3> This study included 65 ACD patients with 1- or 2-year follow-up. <h3>OUTCOME MEASURES</h3> Radiographic alignment, range of motion (ROM). <h3>Methods</h3> CD patients undergoing surgery short of the occiput and the pelvis were included. In addition to the classic alignment parameters, ROM and reserve of extension were calculated across the C2-C7 and C0-C2 segments. After describing the cohort in terms of preoperative information, correlations and hierarchical stepwise regressions investigated the association between C2-C7 correction and change in C0-C2 reserve of extension while controlling for maintenance of horizontal gaze. Stratification by ΔC2-C7 percentile was conducted followed by paired t-tests to investigate changes in TK, C0-C2 and reserve of extension within each percentile. <h3>Results</h3> Sixty-five patients were included (61.8yo±9.6, 68%F). At baseline, they presented with a cervical kyphotic alignment (C2-C7: -11.7°±18.2; TS-CL: 38.6°±18.6), a negative global alignment (SVA: -12mm±71), and hyperlordosis at C0-C2 (33.2°±11.8). The ROM was 25.7°±17.7 and 21.3°±9.9 at C2-C7 and C0-C2, respectively, with an associated reserve of extension of ∼9° for each segment. Limited C0-C2 ROM and reserve of extension significantly correlated with the Neck Disability Index (r=-0.371 & -0.394) and with decreased general health (r=0.455 & 0.512) (all p<0.005) The mean number of levels treated was 7.0±3.1 (24.6% ACDF, 43.1% posterior), with 49.2% of the patients receiving an osteotomy, and 16.9% a 3CO. At 1 year, C2-C7 increased to 5.5°±13.4, SVA became neutral (12mm±54), C0-C2 decreased to 27.7°±11.7, and TK increased to -49.4±18.1 (all p <0.001). At C2-C7 ROM decreased significantly to 9.5°±14.1, and increased to 27.6°±8.1 at C0-C2 without change in reserve of extension. The horizontal gaze significantly improved (4.5±13.3 vs -0.5±9.3 p=0.003). Controlling horizontal gaze, change in C2-C7 lordosis significantly correlated with increased TK (r=-0.615, p<0.01), decreased C0-C2 (r=-0.686, p<0.001), and increased C0-C2 reserve of extension (r=0.414, p<0.015). Larger C0-C2 ROM and reserve of extension correlated with decreased in Neck Disability Index (r=-0.571 & -0.470 p<0.05). Stratification by ΔC2-C7 percentile highlighted the reciprocal change above and below the fusion. Within the lowest percentile (ΔC2-C7: 2°±9.6), no significant difference was noticed between pre and 1 year, while within the highest percentile (ΔC2-C7: -42.8±14.1), C0-C2 decreased (-9.7°±10.5, p=0.001), TK kyphosis increased (14.3°±7.5, p<0.001) and C0-C2 reserve of extension increased (5.8°±6.4, p=0.026). Subanalysis on patients with available 2-year data (N=42) demonstrated similar trends. <h3>Conclusions</h3> Correction of cervical malalignment can significantly impact proximal (C0-C2) and distal (T2-T12) compensation. Restoration of a more natural alignment resulted in an increase of the reserve of extension between C0-C2 and was associated with improved clinical outcomes. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.