The Importance of C2-Slope, a Singular Marker of Cervical Deformity, Correlates with Patient Reported Outcomes.

STUDY DESIGN: Retrospective review of a prospectively-collected database. OBJECTIVE: To define a simplified singular measure of cervical deformity (CD), C2 slope (C2S), which correlates with post-operative outcomes. SUMMARY OF BACKGROUND DATA: Sagittal malalignment of the cervical spine, defined by the cervical sagittal vertical axis (cSVA), has been associated with poor outcomes following surgical correction of the deformity. There has been a proliferation of parameters to describe cervical deformity (CD). This added complexity can lead to confusion in classifying, treating and assessing outcomes of CD surgery. METHODS: A prospective database of CD patients was analyzed. Inclusion criteria were cervical kyphosis\u3e10°, cervical scoliosis\u3e10°, cSVA\u3e4 cm, or chin-brow vertical angle (CBVA) \u3e25°. Patients were categorized into two groups and compared based on whether the apex of the deformity was in the cervical (C) or the cervicothoracic (CT) region. Radiographic parameters were correlated to C2S, T1-slope (T1S) and 1-year health-related quality-of-life (HRQL) outcomes as measured by the EuroQol 5 Dimension questionnaire (EQ5D), modified Japanese Orthopedic Association Scale (mJOA), numeric rating scale for neck pain (NRS neck), and the Neck Disability Index (NDI). RESULTS: 104 CD patients (C = 74, CT = 30; mean age 61y, 56% women, 42% revisions) were included. CT patients had higher baseline cSVA and T1S (p \u3c 0.05). C2S correlated with T1 slope minus cervical lordosis (TS-CL) (r = 0.98, p \u3c 0.001) and C0-C2 angle, cSVA, CL, T1S (r = 0.37-0.65, p \u3c .001). Correlation of cSVA with C0-C2 was weaker (r = 0.48, p \u3c .001). At 1-year postoperatively, higher C2S correlated with worse EQ-5D (r = 0.28, p = .02); in CT patients, higher C2S correlated with worse NDI, mJOA, NRS neck and EQ5D (all r \u3e 0.5, p≤.05). Using linear regression, moderate disability by EQ5D corresponded to C2S of 20°(r = 0.08). For CT patients, C2S = 17° corresponded to moderate disability by NDI (r = 0.4), and C2S = 20° by EQ5D (r = 0.25). CONCLUSION: C2S correlated with upper-cervical and subaxial alignment. C2S correlated strongly with TS-CL (R = .98, p \u3c .001) because C2S is a mathematical approximation of TS-CL. C2S is a useful marker of CD, linking the occipitocervical and cervico-thoracic spine. C2S defines the presence of a mismatch between cervical lordosis and thoracolumbar alignment. Worse 1-year postoperative C2 slope correlated with worse health outcomes. LEVEL OF EVIDENCE: 3