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Curve Progression in Idiopathic Scoliosis: Follow-up Study to Skeletal Maturity

Tan, Ken-Jin MBBS, MMed, MRCS*; Moe, Maung Maung MBBS*; Vaithinathan, Rose MBBS, MMed†; Wong, Hee-Kit MBBS, FRCS*

doi: 10.1097/BRS.0b013e31819c9431
Deformity

Study Design. This is a follow-up study to skeletal maturity on a cohort of students screened for a 1-year prospective epidemiological prevalence study for scoliosis.

Objectives. This study aims to identify the prognostic factors for curve progression to a magnitude of 30° at skeletal maturity in skeletally immature patients with adolescent idiopathic scoliosis.

Summary of Background Data. The natural history of idiopathic scoliosis is not well understood. Previous reports have focused on the characteristics of curve progression where progression has been predefined at specific angles of 5° to 6°. However, the absolute curve magnitude at skeletal maturity is more predictive of long-term curve behavior rather than curve progression of a defined magnitude over shorter periods of skeletal growth. It is generally agreed that curves less than 30° are highly unlikely to progress after skeletal maturity. Hence, defining the factors that influence curve progression to an absolute magnitude of more than 30° at skeletal maturity would more significantly aid clinical practice.

Methods. One hundred eighty-six patients who fulfilled the study criteria were selected from an initial 279 patients with idiopathic scoliosis detected by school screening, and who were followed-up till skeletal maturity. The initial age, gender, pubertal status, and initial curve magnitude were used as risk factors to predict the probability of curve progression to more than 30° at skeletal maturity.

Results. Curve magnitude at first presentation was the most important predictive factor for curve progression to a magnitude of more than 30° at skeletal maturity. An initial Cobb angle of 25° had the best receiver-operating characteristic of 0.80 with a positive predictive value of 68.4% and a negative predictive value of 91.9% for curve progression to 30° or more at skeletal maturity.

Conclusion. Initial Cobb angle magnitude is the most important predictor of long-term curve progression and behavior past skeletal maturity. We suggest an initial Cobb angle of 25° as an important threshold magnitude for long-term curve progression. Initial age, gender, and pubertal status were less important prognostic factors in our study.

Previous studies on the natural history of idiopathic scoliosis that identify risk factors for curve progression based on a defined magnitude may not provide accurate information on long-term curve behavior. We identified curve magnitude at presentation as the most important predictor of curve progression to a threshold Cobb angle of 30° at skeletal maturity. An initial curve of less than 25° is the single most important predictor for long-term curve progression. Initial age, gender, and pubertal status were less important.

From the *Department of Orthopaedic Surgery, National University Hospital, National University of Singapore, Singapore; and †Health Promotion Board, School Health Service, Singapore.

Acknowledgment date: May 12, 2008. Acceptance date: October 21, 2008.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Ken-Jin Tan, MBBS, MMed, MRCS, Department of Orthopaedic Surgery, National University Hospital, 5 Lower Kent Ridge Road, Main Building 1, Singapore 119074, Singapore; E-mail: jinmi@pacific.net.sg

© 2009 Lippincott Williams & Wilkins, Inc.