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Spinal growth and a histologic evaluation of the Risser grade in idiopathic scoliosis.

STUDY DESIGN
Thirty-four patients with idiopathic scoliosis who underwent anterior spinal surgery as part of the correction of spinal deformity were studied prospectively. Superior and inferior endplates were harvested and examined histologically for evidence of residual growth activity. This was then correlated with Risser grades, chronologic age, and pubertal status.


OBJECTIVES
To clarify the correlation between Risser grade and vertebral endplate growth potential in patients with idiopathic scoliosis.


SUMMARY OF BACKGROUND DATA
The importance of longitudinal spinal growth in patients with idiopathic scoliosis and its correlation with curve progression and the crankshaft phenomenon after posterior fusion are well recognized. The Risser grade, which shows the extent of excursion of the iliac apophysis on serial plain radiographs, is commonly used to estimate residual spinal growth. However, the correlation between the Risser grade and vertebral endplate growth potential in patients with idiopathic scoliosis remains unclear.


METHODS
Superior and inferior endplates were harvested from these patients and examined histologically for evidence of residual growth. This was correlated with Risser grade, chronologic age, and pubertal status.


RESULTS
Risser Grade 5 was found to be the only indicator of cessation of vertebral growth in idiopathic scoliosis. Of the 14 patients with Risser Grade 4, 10 showed significant growth activity in the vertebral endplates. The reliability of Risser Grade 4 increases when combined with chronologic age and time since menarche in female patients.


CONCLUSIONS
The crankshaft phenomenon is reported to occur only in patients with Risser Grade 2 or less, particularly those with open triradiate cartilages. Our findings of significant endplate growth activity, even in patients with Risser Grade 4, make it unlikely that the crankshaft phenomenon is caused purely by longitudinal spinal growth.