Spontaneous lumbar curve correction in selective thoracic fusions of idiopathic scoliosis - A comparison of anterior and posterior approaches

Study Design. A retrospective evaluation of adolescent idiopathic scoliosis (AIS) patients treated with selective thoracic instrumentation and fusion. Objective. To evaluate the predictors and the effect of surgical approach (anterior versus posterior) on spontaneous lumbar curve correction (SLCC) after selective thoracic fusion in patients with structural thoracic and compensatory lumbar curves. Summary of Background Data. Spontaneous coronal correction of the unfused lumbar curve has been described previously; however controversy continues regarding the effect of surgical approach on SLCC. Methods. One hundred thirty-two anterior and 44 posterior selective thoracic fusions instrumented distally to T11, T12, or L1 were identified from a multicenter AIS database. A 2-way ANOVA was used to compare SLCC with regards to surgical approach and the lowest instrumented vertebra (LIV). A Pearson's correlation analysis was utilized to identify radiographic variables associated with SLCC. A secondary analysis of surgical approach was then performed on 28 pairs of patients matching the factors that correlated positively with SLCC. Results. The average SLCC for the anterior approach (44% +/- 19%) was less than that for the posterior approach (49% +/- 19%; P = 0.07), and was found to increase significantly with a more distal LIV (P = 0.03). Pearson's correlation analysis revealed the strongest correlations between SLCC and preoperative lumbar curve flexibility (r = 0.20) and 2-year postoperative thoracic curve percent correction (r = 0.47). A secondary analysis of SLCC in paired curves matched by LIV, lumbar curve flexibility and thoracic percent correction revealed no difference between anterior (48%) and posterior (49%) approaches (P = 0.75). Conclusion. Anterior and posterior instrumented fusions performed selectively on the appropriate curves result in equal SLCC when matched by LIV, flexibility of the lumbar curve, and percent thoracic curve correction achieved. This suggests that the observed phenomenon of SLCC after selective thoracic fusion in AIS is independent of surgical approach and can be reliably achieved with either technique.