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Residual Thoracic Hypokyphosis Following Posterior Spinal Fusion in Adolescent Idiopathic Scoliosis: Risk Factors and Clinical Ramifications: Paper #17

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

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United States

Summary: We assessed risk factors for persistent thoracic hypokyphosis following posterior spinal fusion for adolescent idiopathic scoliosis (AIS) and to compare clinical outcomes between patients with residual thoracic hypokyphosis and those with normal kyphosis. Risk factors for residual thoracic HK included preoperative thoracic hypokyphosis and curves with less main thoracic scoliosis. The use of smaller rods and pedicle screws was also associated with persistent hypokyphosis. Clinical outcomes were no different in the hypokyphotic group than in the normokyphotic patients.

Introduction: Adolescent idiopathic scoliosis (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: A review of a consecutive prospective series of patients at a single institution with AIS and a primary structural main thoracic (MT) curve who underwent PSF was performed. A radiographic and clinical assessment using the Scoliosis Research Society (SRS) 30 and Spinal Appearance Questionnaire (SAQ) were performed preoperatively and at 2 years. Patients were divided into two groups based on a threshold of 20° of thoracic kyphosis measured at two years follow up: <20° (HK group) and normal kyphosis >20° (NK group).

Results: There were 214 patients with an average age of 14.5 years with a T5‐T12 kyphosis of 18.9° and a MT coronal curve of 60.9° preoperatively. Residual hypokyphosis <20° was seen in 83 (38.8%) patients. Preoperative risk factors for being hypokyphotic at 2 years were: male gender (21.69% vs 12.21%, p=0.084), preoperative kyphosis (11.4° vs 22.8°, p<0.0001) and smaller preoperative MT coronal curves (58.4° vs 62.0°, p=0.004). 71.5% of patients instrumented with 6.35mm rods were kyphotic at two years compared to 47.0% instrumented with 5.5mm rods (p=0.0043). 64.7% of patients with all‐pedicle screw constructs remained hypokyphotic compared to 36.6% with hybrid constructs (p=0.035). There was no difference in proximal junctional kyphosis between groups(T2‐T5: 11.6° (HK) vs 11.1° (NK), p=0.71) but thoracolumbar lordosis (T10‐L2) was increased in the HK group (‐8.0°(HK) vs ‐2.8°(NK),p=0.0004). Both groups had similar clinical results on the SRS‐30 and SAQ at two year follow up (P>0.05).

Conclusion: Scoliosis patients with persistent thoracic hypokyphosis are usually hypokyphotic preoperatively and are more likely to have a smaller MT curve, perhaps due to less contouring of the rod prior to rod rotation. Use of pedicle screws and 5.5mm rods increased the risk of having residual hypokyphosis. Hypokyphosis did not seem to decrease clinical outcomes at two year follow up.

The FDA has not cleared the drug and/or medical device for the use described in this presentation (i.e., the drug or medical device is being discussed for an ‘off label’ use).

© 2010 Lippincott Williams & Wilkins, Inc.

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