Preventing the Crankshaft Phenomenon by Combining Anterior Fusion With Posterior Instrumentation

Abstract

Study Design. Fourteen skeletally immature patients with idiopathic scoliosis (Group I) were retrospectively studied to determine if the crankshaft phenomenon was prevented by combining anterior spinal fusion with posterior instrumentation and fusion. They were compared with 12 similar patients who underwent posterior procedures only (Group II). Objectives. To determine whether the addition of anterior spinal fusion was beneficial in preventing progressive spinal deformity in the very young patient. Summary of Background Data. The crankshaft phenomenon had been well documented in young patients undergoing posterior fusion only. No previous study compared the results of a similar group of patients some of whom underwent combined anterior and posterior fusion and the others who underwent posterior fusion only. Methods. Patients who were Risser 0 and had open triradiate cartilages at surgery were evaluated for curve correction, correction loss, changes in rib vertebral angle differences, rotational changes, and spinal balance. Crankshaft was defined as a progression in curve magnitude greater than 10° and accompanied by an increase in rib vertebral angle difference greater than 10°. In Group I, age at surgery averaged 10.7 years, and follow-up averaged 37 months. In Group II, age at surgery averaged 11.0 years, and follow-up averaged 64 months. Results. Group I: Thoracic curve correction averaged 77% after surgery and 68% at follow-up. At follow-up, two patients had curves progress more than 10°, and three patients had an increase in rib vertebral angle difference of 10° or more, but none of the patients had these changes simultaneously. Group II: During the course of follow-up, five of the 12 patients had progressive changes of 10° or more in curve size and rib vertebral angle difference. Four other patients had an increase exceeding 10° in one of the two categories. Conclusions. In skeletally immature children (open triradiate cartilage and Risser 0) with idiopathic scoliosis, the addition of anterior spinal fusion to posterior instrumentation and fusion is helpful in preventing the crankshaft phenomenon.