186. FACTORS PREDICTIVE OF CURVE PROGRESSION AND TIMING OF DEFINITIVE FUSION IN EARLY ONSET SCOLIOSIS (EOS) TREATED BY GROWING ROD (GR) CONSTRUCT

Abstract

Purpose: To report long-term results (with a minimum follow-up of 13 years) of GR construct [Luque-trolley (LT)] in EOS, to identify factors predictive of curve progression and to establish the timing of definitive fusion.

Method: The study cohort consisted of 37 patients (22M & 15F) who had primary LT between 1983–1995 were reviewed. Group I: 7 patients had LT alone and Group II: 30 had LT with convex fusion. Cobb at initial presentation, after first surgery, before definitive fusion and at the latest follow-up was recorded. Other radiological curve parameters recorded were rib spinal angle difference (RSAD), end vertebral tilts (EVT), apical vertebral rotation (AVR) and T1-S1 length. Complications with respect to development of junctional/apical kyphosis, implant failure, pseudoarthrosis (PA), sagittal/coronal profile and instrumented spinal segment growth at maturity were evaluated.

Results: The mean age at definitive fusion for study cohort was 12.5 years. Group I: Mean age at first surgery was 7.4 years (3.3–9.5y). Mean pre-op Cobb angle of primary curve was 600 (310–710) which was corrected to 280 (200–360). They underwent definitive segmental spinal instrumentation(SSI) with fusion at 13.9 years (9.8–15.1y) when the curve had worsened to 480 (400–650). Group II: Mean age at index surgery was 3.6 years (1.6–8.8y). Mean pre-op Cobb of primary curve was 580 (300–900) which corrected to 300 (100–620). 16/30 patients underwent definitive SSI with fusion at 11.5 years (8.5–14.2y) when the curve deteriorated to 600 (530–770). Instrumented segmental spinal growth was 3.2cms (SD±1.45; range 1–5cms). 14/30 maintained their correction till skeletal maturity. JK was observed in 8 cases [proximal(3), distal(2) & apical(3)] which were corrected at the time of definitive SSI. There was a linear relationship between Cobb angle at definitive fusion with concaveRSA and upperEVT.

Conclusion: Correlation and regression statistics revealed predictive factors of curve progression to be concave RSA (®=0.91 & p=0.001) and upper EVT (®=0.81 & p=0.0004). Patients with high concave RSA and upper EVT should be closely monitored for deterioration. Spinal growth that exceeds the capacity of LT to elongate leads to apical kyphosis. Timing of definitive fusion is influenced by growth velocity, clinico-radiological factors and complications.