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

By London Spine

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

Spine (Phila Pa 1976). 2011 Feb 25;

Authors: Fletcher ND, Hopkins J, McClung A, Browne R, Sucato DJ

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 following posterior spinal fusion and instrumentation (PSFI) for AIS and to compare clinical outcomes between patients with residual thoracic hypokyphosis and those with normal thoracic kyphosis following PSFI for AIS.Summary of background data: 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: Radiographic and clinical assessment using the Scoliosis Research Society (SRS) 30 and Spinal Appearance Questionnaire (SAQ) was done preoperatively and at 2 years. Patients were divided into two groups based on a threshold of 20° of thoracic kyphosis measured between T5 and T12 at two years follow up.Results: 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 had normal thoracic kyphosis at two years compared to 47.0% instrumented with 5.5mm rods (p = 0.0043). All-pedicle screw constructs remained hypokyphotic compared to hook based constructs (p = 0.035). Logistic regression analysis demonstrated two 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 two year follow up (P>0.05). There was a small but statistically significant correlation between sagittal Cobb angle and clinical deformity at two years based on the sagittal components of the SAQ.Conclusions: There are two risk factors which 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 degrees, these patients did not have decreased clinical outcomes as measured by the SRS-30 or SAQ.

PMID: 21358571 [PubMed – as supplied by publisher]