Flatback Revisited: Reciprocal Loss of Lumbar Lordosis Following Selective Thoracic Fusion in the Setting of Adolescent Idiopathic Scoliosis

Study DesignRetrospective review of prospective multicenter adolescent idiopathic scoliosis (AIS) database.ObjectiveTo investigate the relationship between iatrogenic loss of thoracic kyphosis (TK) after selective thoracic posterior spinal instrumentation and fusion (PSIF) for AIS with straightening of lumbar lordosis (LL).Summary of Background DataSegmental PSIF has become the standard of care for surgical treatment of severe AIS. Studies show that adults with flattening of TK and LL can develop pain and dysfunction associated with flatback syndrome. Analysis of post-fusion sagittal alignment is lacking in the AIS population.MethodsQuery of prospective multicenter database for AIS patients with Lenke 1, 2, or 3 curves who underwent selective thoracic PSIF (lowest instrumented vertebra equal or cephalad to L1) identified 123 patients with a minimum of 2 years' follow-up. Thoracic kyphosis (T5–T12), LL (T12–S1), and global sagittal alignment were measured preoperatively and at 2 years postoperatively. Health-related quality of life measures were examined.ResultsA total of 31% of patients had loss of TK and 42% lost LL. Patients with decreased TK had significantly higher rates of decreased LL (68%) than patients without decreased TK (31%). Multivariate regression confirmed that TK had significant predictive effect on LL (p < .001). Specifically, change in TK of 2° was associated with roughly 3° change in LL. There were no significant associations between changes in TK or LL and health-related quality of life.ConclusionsLoss of TK occurs commonly in selective fusion for AIS. This loss of kyphosis is strongly associated with reciprocal loss of LL. Spinal fusion can have unintended effects on sagittal alignment; these effects may have consequences that remain to be fully elucidated.