Analysis of cervical sagittal alignment change following correction of thoracic and thoracolumbar Scheuermann's kyphosis

PURPOSE: To analyse pre-operative and post-operative changes of cervical sagittal alignment (CSA) in Scheuermann's kyphosis (SK) patients. METHODS: 64 SK and 33 control patients were retrospectively reviewed. Whole spine X-rays obtained at pre-op, 3 months post-op and at latest follow-up were reviewed and ten separate CSA radiological parameters were measured. Patients were divided in three groups: thoracic SK (TK group, apex T6-T9, n = 40), thoracolumbar SK (TLK group, apex T10-T12, n = 24), and controls. RESULTS: Pre-operative C2-C7 lordosis was 21.1° ± 8.1°(TK), 6.1° ± 5.0°(TLK), and 11.4° ± 8.3° in control group and correlated significantly with T1 slope in both SK groups (r = 0.640, r = 0.772). Pre-operative T1 slope was dependent on deformity type, thoracic kyphosis (TK, β = 0.445), and lumbar lordosis (LL, β = -0.354). At final follow-up C2-C7 lordosis decreased to 15.7° ± 5.5° in TK, and increased to 12.1° ± 4.1° in TLK group. C2-C7 lordosis changes linearly correlated with T1 slope changes post-operatively (r = 0.721). Post-operative T1 slope showed linear correlation with post-operative changes in TK (β = 0.728) and pelvic tilt (PT, β = 0.539) in TK, and LL (β = -0.669), thoracolumbar kyphosis (TLK, β = -0.434), and PT (β = 0.760) in TLK group. CONCLUSIONS: Our study suggests that SK is not a homogenous group of patients. Two patterns of pre- and post-operative CSA are demonstrated in TK and TLK groups. T1 slope is the most important parameter in determining pre-operative CSA and correlates with other regional anatomical parameters (TK and LL). Post-operative CSA adaptations also correlate with T1 slope post-operative changes. However, post-surgical T1 slope correlates with different parameters in the two SK groups (TK and PT in TK group; TLK, LL, and PT in TLK group).