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Residual Thoracic Hypokyphosis After Posterior Spinal Fusion and Instrumentation in Adolescent Idiopathic Scoliosis: Risk Factors and Clinical Ramifications

Fletcher, Nicholas D. MD; Jeffrey, Hopkins MSN, RN; Anna, McClung RN; Browne, Richard PhD; Sucato, Daniel J. MD, MS

doi: 10.1097/BRS.0b013e318216106c

Study Design. A retrospective review of clinical and radiographic data from a single-center, prospectively collected scoliosis database.

Objective. To assess risk factors for persistent thoracic hypokyphosis after posterior spinal fusion and instrumentation (PSFI) for adolescent idiopathic scoliosis (AIS) and to compare clinical outcomes between patients with residual thoracic hypokyphosis and those with normal thoracic kyphosis after PSFI for AIS.

Summary of Background Data. AIS is characterized by thoracic hypokyphosis, which should be corrected at the time of surgical treatment. Risk factors for residual thoracic hypokyphosis and the clinical ramifications have not been studied.

Methods. Radiographic and clinical assessments by using the Scoliosis Research Society-30 (SRS-30) and Spinal Appearance Questionnaire (SAQ) were done preoperatively and at 2 years. Patients were divided into 2 groups on the basis of a threshold of 20° of thoracic kyphosis measured between T5 and T12 at 2-year follow-up.

Results. Risk factors for being hypokyphotic at 2 years were male sex (21.69% vs. 12.21%, P = 0.084), preoperative kyphosis (11.4° vs. 22.8°, P < 0.0001), and smaller preoperative main thoracic coronal curves (58.4° vs. 62.0°, P = 0.004). A total of 71.5% of patients instrumented with 6.35-mm rods had normal thoracic kyphosis at 2 years compared with 47.0% instrumented with 5.5-mm rods (P = 0.0043). All-pedicle screw constructs remained hypokyphotic compared with hook-based constructs (P = 0.035). Logistic regression analysis demonstrated 2 parameters associated with persistent thoracic hypokyphosis at 2 years: preoperative hypokyphosis and larger rod diameter. Both groups had similar clinical results on the SRS-30 at 2-year follow-up (P > 0.05). There was a small but statistically significant correlation between sagittal Cobb angle and clinical deformity at 2 years based on the sagittal components of the SAQ.

Conclusion. There are 2 risk factors that lead to thoracic hypokyphosis in AIS: preoperative hypokyphosis and use of a 5.5-mm-diameter rod. A larger-diameter rod should be considered when planning surgery for thoracic AIS, especially when there is preoperative hypokyphosis. Despite thoracic kyphosis measuring less than 20°, these patients did not have decreased clinical outcomes as measured by the SRS-30 or SAQ.

Residual thoracic hypokyphosis after posterior spinal fusion and instrumentation (PSFI) for adolescent idiopathic scoliosis (AIS) was more common in men and with the use of pedicle screw and smaller rods. Preoperative hypokyphosis and smaller coronal thoracic scoliosis also correlated with residual thoracic hypokyphosis. The clinical significance of postoperative hypokyphosis remains uncertain.

From the Texas Scottish Rite Hospital for Children, Dallas, Texas.

Address correspondence and reprint requests to Daniel J. Sucato, MD, MS, Texas Scottish Rite Hospital for Children, 2222 Welborn St, Dallas, TX 75219; E-mail:

Acknowledgment date: June 23, 2010. First revise date: July 29, 2010. Second revise date: February 7, 2011. Acceptance date: February 10, 2011.

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

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.

© 2012 Lippincott Williams & Wilkins, Inc.