Prospective multi-centric evaluation of upper cervical and infra-cervical sagittal compensatory alignment in patients with adult cervical deformity.

Abstract

Reciprocal mechanisms for standing alignment have been described in thoraco-lumbar deformity but have not been studied in patients with primary cervical deformity (CD). The purpose of this study is to report upper- and infra-cervical sagittal compensatory mechanisms in patients with CD and evaluate their changes post-operatively. Global spinal alignment was studied in a prospective database of operative CD patients. Inclusion criteria were any of the following: cervical kyphosis (CK)>10°, cervical scoliosis>10°, cSVA (C2-C7 Sagittal vertical axis)>4cm or CBVA (Chin Brow Vertical Angle)>25°. For this study, patients who had previous fusion outside C2 to T4 segments were excluded. Patients were sub-classified by increasing severity of cervical kyphosis [CL (cervical lordosis):<0°, CK-low 0°-10°, CK-high>10°] and cSVA (cSVA-low 0-4cm, cSVA-mid 4-6cm, cSVA-high>6cm) and were compared for pre- and 3-month post-operative regional and global sagittal alignment to determine compensatory recruitment. 75 CD patients (mean age 61.3 years, 56% women) were included. Patients with progressively larger CK had a progressive increase in C0-C2 (CL=34°, CK-low=37°, CK-high=44°, p=0.004), C2Slope and T1Slope-CL (p<0.05). As the cSVA increased, there was progressive increase in C2Slope, T1Slope and TS-CL (p<0.05) and patients compensated through increasing C0-C2 (cSVA-low=33°, cSVA-mid=40°, cSVA-high=43°, p=0.007) and pelvic tilt (cSVA-low=14.9°, cSVA-mid=24.1°, cSVA-high=24.9°, p=0.02). At 3months post-op, with significant improvement in cervical alignment, there was relaxation of C0-C2 (39°-35°, p=0.01) which positively correlated with magnitude of deformity correction. Patients with cervical malalignment compensate with upper cervical hyper-lordosis, presumably for the maintenance of horizontal gaze. As cSVA increases, patients also tend to exhibit increased pelvic retroversion. Following surgical treatment, there was relaxation of upper cervical compensation.