POSTERIOR ARTHRODESIS IN THE SKELETALLY IMMATURE PATIENT - ASSESSING THE RISK FOR CRANKSHAFT - IS AN OPEN TRIRADIATE CARTILAGE THE ANSWER

Study Design. Thirty-three skeletally immature patients younger than 1 2 years of age and having posterior arthrodesis and evidence of solid posterior fusion without ''adding on'' were retrospectively reviewed. All patients had a minimum of 5 years of follow-up. Objectives. To asc ertain factors associated with crankshaft and to determine how accurat e a marker the triradiate cartilage was. Summary of Data. All patients had Risser Stage 0 curves and all of the girls were premenarchal preo peratively, the average age was 9 years 3 months (range, 2 years-11 ye ars 11 months). Preoperative diagnoses consisted of 14 idiopathic, 11 congenital, five dysplastic, and three neuromuscular etiologies. Metho ds. Preoperatively, within 3 months after surgery, and at 2-year, 5-ye ar, and final postoperative follow-up, the following radiographic para meters were reviewed: coronal Cobb, apical vertebral rotation, apical vertebral translation, rib vertebral angle difference, and trunkshift. Results. The triradiate cartilage was open in 24 patients at the time of operation. Of those 24, only nine (37.5%) had documented proof of crankshaft. Patients with closed triradiate cartilage had no significa nt postoperative increase in radiographic parameters (0 of 9). The sub group of patients with idiopathic scoliosis had an average age of 11 y ears 3 months (range, 9 years 2 months-11 years 11 months). Five of 14 patients had an open triradiate cartilage. All were followed up to sk eletal maturity. None had significant progression in postoperative rad iographic parameters. Conclusion. This study did not find an open trir adiate cartilage to be an absolute prognostic indicator for the occurr ence of crankshaft. Additional refinement of markers of maturity are n eeded to determine who requires anterior arthrodesis.