Scoliosis correction maintenance in skeletally immature patients with idiopathic scoliosis - Is anterior fusion really necessary?

Study Design, A retrospective evaluation of the occurrence of the crankshaf t phenomenon in skeletally immature patients with idiopathic scoliosis. Objective. To determine what factors, if any, contribute to a decreased occ urrence of cranshaft phenomenon in patients treated with posterior surgery only. Summary of Background Data, Reports have described the progression of scoli otic deformity, termed the crankshaft phenomenon, in a region of solid post erior arthrodesis in skeletally immature patients. This has led some author s to advocate the use of concomitant anterior discectomy and fusion to prev ent crankshaft, Methods. From 1989 through 1994, 28 Risser 0 patients with thoracic or thor acolumbar idiopathic scoliosis underwent Isola (De Puy-Acromed, Raynham, MA ) posterior instrumentation and fusion. They were assessed for evidence of the crankshaft phenomenon, identified by coronal plane deformity progressio n of 10 degrees or more, or a rib vertebra angle difference of 10 degrees o r more. The average age of the patients was 12.5 years (range, 10.5-15.5 ye ars), and the average follow-up period was 39 months (range, 24-68 months). Results. Eleven patients(10 girls and 1 boy) had closed triradiate cartilag e at the time of surgery. Their average Cobb angle was 62 degrees before su rgery, 21 degrees after surgery, and 22 degrees at follow-up assessment. No patients in this group met the criteria for crankshaft, Seven patients (6 girls and 1 boy) had open triradiate cartilage at the time of surgery. Thei r average Cobb angle was 62 degrees before surgery, 18 degrees after surger y, and 20 degrees at follow-up evaluation. No patient had a 10 degrees or m ore increase in rib vertebra angle difference. One patient had more than a 10 degrees increase in her Cobb angle (11 degrees) from postoperative to la test follow-up assessment. Her instrumentation construct, performed in 1989 , used sublaminar wires as the caudal anchors. Hooks and pedicle screws are now used. Two of the seven patients with open triradiate cartilage underwe nt surgery during or before their peak height velocity and displayed no evi dence of crankshaft. No deaths, neurologic complications, or infections occ urred in either group. Conclusions. These findings suggest that scoliotic deformity progression ca n be prevented in skeletally immature patients with idiopathic scoliosis as young as 10 years of age with the use of stiff segmental posterior instrum entation, without the necessity of concomitant anterior arthrodesis.