The role of the fractional lumbosacral curve in persistent coronal malalignment following adult thoracolumbar deformity surgery: a radiographic analysis

Study design: Retrospective cohort. Objective: Assess radiographically the effect of an all-posterior approach on correction of coronal balance in primary adult thoracolumbar spinal deformities based on Bao’s classification of coronal imbalance with a focus on lumbosacral curve correction. Summary of background data: Achieving appropriate coronal alignment is difficult in adults with coronal malalignment due to trunk shift ipsilateral to degenerated thoracolumbar scoliosis’ apex. Methods: Review of adults who underwent posterior spinal fusions to pelvis (≥ 5 levels) for thoracolumbar scoliosis. Exclusion: revisions, no coronal deformity, thoracic Cobb > 30°, and anterior operations. Patients were divided into three groups, as proposed by Bao et al.: type A: CSVL < 3 cm; type B: CSVL > 3 cm and C7 plumb shifted to scoliosis’ concavity; type C: CSVL > 3 cm and C7 plumb shifted to scoliosis’ convexity. Radiographic parameters and surgical techniques were compared. Results: 124 patients (male-6; female-118; avg. age 58 ± 10 years; type A-87; type B-19; type C-18). Type C had significantly greater lumbosacral fractional curves. 28% of type C were treated with fractional curve TLIFs, while all, but one, type B had TLIFs of the fractional curve. Deformity parameters after surgery were similar, except type C had persistently greater fractional curves/coronal malalignment. All preop type B were appropriately corrected postop. For preop type C, 67% remained type C and 33% became type A postop. Compared to those who became type A, persistently undercorrected and malaligned (type C) patients had significantly greater preop lumbosacral fractional curves, greater preop coronal Cobb angles, and more commonly involved TLIFs of lumbosacral fractional curves. Compared to no interbody support, use of TLIFs provided better correction of the lumbosacral curve. Conclusions: In adults with primary, posterior-only operations for thoracolumbar spinal deformity, 67% of type C coronal deformities and 20% of type A deformities remained or had worse coronal malalignment postop. While the use of TLIFs improved correction of the lumbosacral curve compared to no interbody support, alternative surgical strategies should be considered to more adequately correct lumbosacral fractional curves and balance correction of lumbosacral and major thoracolumbar curves so as to maintain and/or restore coronal balance. Level of evidence: III.