Spontaneous correction and derotation of secondary curves after selective anterior fusion of idiopathic scoliosis

Abstract

Study design: Clinical, rasterstereographic, and radiographic evaluation of spontaneous vertebral derotation of secondary curves in idiopathic scoliosis following selective anterior correction and fusion of the primary curve.

Objective: To quantify spontaneous vertebral derotation in secondary curves after selective anterior correction with attention to cosmetic outcome.

Summary of background data: While the derotational effect of anterior instrumentation techniques on the instrumented curve is well understood, there is a paucity on data of the rotational behavior of the noninstrumented secondary curves.

Methods: A total of 43 patients with idiopathic scoliosis (16 with thoracic curves in group 1 and 27 with thoracolumbar/lumbar curves in group 2) underwent selective anterior instrumentation. Vertebral rotation was analyzed before surgery and, on average, 20 months after surgery using digital radiometric rotation analysis, back shape analysis with rasterstereography, and scoliometer measurement.

Results: In Group 1, there was a significant spontaneous vertebral derotation of the secondary lumbar curves by 14.2% (range from 12.7 degrees to 10.9 degrees) in the digital radiometric rotation analysis, surface derotation amounted to 49% (range from 9.6 degrees to 4.9 degrees) in the rasterstereography, and to 70% in the clinical scoliometer measurement (range from 8.0 degrees to 2.4 degrees ). In group 2, there was an increase of rotation of the noninstrumented secondary thoracic curves by 30% (range from 5.0 degrees to 6.5 degrees ) in digital radiometry, by 32.9% in the rasterstereography (range from 8.5 degrees to 11.3 degrees), and a 28.3% increase in scoliometer measurement (range from 6.0 degrees to 7.7 degrees).

Conclusion: Selective anterior instrumentation and fusion of primary thoracic curves results in satisfactory spontaneous vertebral and high surface derotation of the secondary lumbar curves. However, in primary thoracolumbar or lumbar curves, an increase of both vertebral and surface rotation of the secondary thoracic curve was noted. This increase can impair cosmetic outcome.