The crankshaft phenomenon after posterior spinal arthrodesis for congenital scoliosis: a review of 54 patients.

STUDY DESIGN: Retrospective chart and radiographic reviews were conducted.

OBJECTIVE: To identify the incidence of and any possible risk factors for the crankshaft phenomenon after posterior spinal arthrodesis for congenital scoliosis.

SUMMARY OF BACKGROUND DATA: Studies have shown the crankshaft problem to be common after posterior arthrodesis for infantile and juvenile idiopathic scoliosis, but the few reports available show it to be much less common for congenital scoliosis.

METHODS: This study chose children fused before the pubertal growth spurt, all classified as Risser 0 and with open triradiate cartilages. These children were followed to the end of their growth (mean follow-up period 12 years). Several measurement parameters were used for evaluation.

RESULTS: The crankshaft problem, measured as a Cobb angle increase of more than 10 degrees, was seen in 15% of the 54 patients. There was a positive correlation with earlier surgery and larger (>50 degrees) curves. No other positive correlations could be identified.

CONCLUSIONS: Crankshafting was observed in 15% of the patients, more often with larger curves and earlier fusions.