General Session: Cervical-1
Presented by: B. Diebo - View Audio/Video Presentation (Members Only)
B. Diebo(1), J. Oren(2), M. Spiegel(2), S. Vira(2), E. Tanzi(2), B. Liabaud(1), R. Lafage(2), J. Henry(2), T. Protopsaltis(2), T. Errico(2), F. Schwab(1), V. Lafage(1)
(1) Hospital for Special Surgery, New York, NY, United States
(2) NYU Hospital for Joint Diseases, Orthopedic Surgery, New York, NY, United States
Summary: Cervical kyphosis is often considered a marker of cervical deformity, but this may not be valid. A formula to predict cervical curvature from underlying thoracolumbar alignment was derived and validated in 1905 patient visits. Kyphosis is required for the maintenance of horizontal gaze in subsets of patients under a certain thoracic kyphosis and sagittal vertical axis. Cervical curvature can be calculated from thoracic kyphosis and lumbar lordosis which can be useful in predicting alignment after thoracolumbar correction.
Hypothesis: Cervical kyphosis may be a physiologic alignment necessary for the maintenance of horizontal gaze depending on underlying thoracolumbar (TL) alignment. Design: Retrospective review
Introduction: Cervical curvature (CC) is affected by thoracic and global alignment. Recent studies suggest large variability in normative CC ranging from lordotic to kyphotic alignment. This study investigates the effect of thoracic and global alignment on CC in maintenance of horizontal gaze.
Methods: For formula development, full body xrays of 744 patients (pts) without presenting cervical complaints or existing fusions higher than T3 were studied. Only pts who maintained their horizontal gaze (CBVA -5° and 17° or McGregor's slope between -6° and 14°) were included. Pts were stratified based on thoracic kyphosis (TK) into (>50, 40-50, 30-40 and < 30). Pts were sub-stratified by SRS-Schwab sagittal vertical axis (SVA) modifier into (posterior alignment SVA< 0, aligned 0-50 and malaligned >50mm). C2-C7 cervical curvature was assessed among SVA grade in every TK group. Stepwise linear regression analysis was applied. A simplified formula was validated on random selection of 1905 patient visits from same database.
Results: In each TK group (n=265, 172, 163, 144), CC was significantly more lordotic by increased Schwab SVA grade (Fig). In SVA < 0, CC was neutral for TK 40-50°, and kyphotic for TK < 40°. All pts with SVA< 50 mm, and TK< 30° were kyphotic. Regression analysis revealed LL minus TK (LL-TK) as an independent predictor (r=0.653, r2=0.426) with formula: CC = 10 - (LL-TK)/2. Validation of the formula revealed error of 1.2° between predicted CC and real CC (r=617, r2=381).
Conclusions: Kyphotic cervical alignment is necessary in the maintenance of horizontal gaze in some well aligned and some sagittal backward pts depending on thoracic curvature. CC can be predicted from underlying TK and lumbar lordosis, which can be clinically relevant in thoracolumbar deformity correction.