POSTERIOR ARTHRODESIS AND INSTRUMENTATION IN THE IMMATURE (RISSER-GRADE-0) SPINE IN IDIOPATHIC SCOLIOSIS

We performed a retrospective study of the long-term results of posteri or instrumentation and arthrodesis of the spine in forty-three patient s who had idiopathic scoliosis and a Risser grade of 0 at the time of the operation. The average age of the patients was 12.4 years (range, 6.7 to 15.5 years) at the time of the operation, The triradiate cartil ages were open in twenty-three patients and closed in twenty. At the t ime of the latest follow-up evaluation (average duration of follow-up, four years; range, two to eleven years), seventeen patients had a Ris ser grade of 5; twenty-two, 4; two, 3; one, 2; and one, 0. The cranksh aft phenomenon, a progressive deformity resulting from continued growt h of the anterior aspect of the spine after posterior arthrodesis, was seen in only one patient who had closed triradiate cartilages and in ten patients who had open triradiate cartilages (p = 0.004). The most common radiographic finding was a progressive rib-vertebra angle diffe rence, which increased more than 10 degrees in seven of the eleven pat ients who had the crankshaft phenomenon, The mean increase in these el even patients was 22 degrees, compared with no increase in the thirty- two other patients (p < 0.0001). Open triradiate cartilages (r = 0.58, p = 0.0001) and a younger age at the time of the operation (p < 0.000 1) were predictive of the amount of progression as a result of the cra nkshaft phenomenon. In patients who had open triradiate cartilages, le ss skeletal maturity was also predictive of progression as a result of the crankshaft phenomenon (r = -0.72, p = 0.0002).