Fusion maturation over time in operated on adolescent idipathic scoliosis - a low dose CT study up to 5 years

The aim of this study was to evaluate bony fusion with Low Dose CT (LDCT) over time following posterior scoliosis surgery in an all screw construct in patients with AIS with special focus on whether the spinal fusion process continue to develop beyond 2 years after scoliosis surgery and to evaluate if LDCT is an adequate radiological method to assess fusion maturation.

Twenty five consecutive patients with mean age 17 (range 13-24) were operated on during 2009-2010 with index diagnosis AIS. Two neuroradiologists used a LDCT protocol to independently evaluate the occurrence and degree of bony fusion at 2 years and 5 years after surgery (ankylosed facet joints). The instrumented spine was divided in an upper, a middle and a lower third on each side in the 25 patients, leaving 150 regions to be assessed. Fusion in each region was classified based on the status of the facet joints as total, partial or non-fusion.

Progression of fusion degree between 2 years and 5 years postoperatively occurred in 18 patients (72%). At 5 years follow-up, 60% showed evidence of total fusion and none showed non-fusion. The interobserver agreement in the classification of bony fusion 2 years postoperatively was almost perfect with a Kappa coefficient of 0.94 and between 2 and 5 years postoperatively a Kappa Coefficient of 0.90.

The fusion maturation progress continues beyond two years following posterior scoliosis surgery in AIS. LDCT is a reliable radiological method to reveal bony fusion maturation over time after posterior scoliosis surgery.