Effects of Continued Posterior Spinal Growth on Sagittal Contour After Anterior Spinal Fusion with Instrumentation of Different Sizes for Adolescent Idiopathic Scoliosis

• (a - DePuy Acromed, Inc.)

Introduction: The previous finding of progressive kyphosis of an average of 15 after anterior spinal fusion using 3.2 mm flexible, threaded rod in skeletally immature patients was not expected. Sixty percent of immature patients who were Risser zero at the time of anterior fusion had more than 10º of sagittal progression during two year follow-up, but this occurred in only 27% of mature (Risser 1-5) patients. To help prevent the occurrence of progressive kyphosis in future patients, the authors began using solid rods of 4.0 mm - 5.5 mm diameter. The purpose of this study is to compare patients who were fused anteriorly with solid rods to those from the previous study using the flexible rod, and assess for the effect of maturity on progressive kyphosis.

Methods: In this retrospective study, patients were drawn from a database of over 1000 patients, using these criteria: thoracic adolescent idiopathic scoliosis, radiographic evidence of solid fusion, no instrumentation failure, adequate biplanar radiographs for review, and minimum two year follow-up. Patients were grouped by type of anterior rod used, and skeletal maturity as determined by Risser stage. Patients in Group I had fusion with flexible rods, while Group II had fusion with solid rods. Ten Group I patients were Risser 0 and 37 were Risser 1-5 at fusion. Fifty-six Group II patients were Risser 0 at fusion, and 144 patients were Risser 1-5. Subgroups were compared for age, preoperative sagittal and coronal curves. Immature Group I patients averaged 12.4 years, Group II 12.7 years. Mature Group I patients averaged 15.4 years, Group II 15.1 years. Sagittal curves in immature Group I patients averaged 11.8º, Group II 19.4º; while mature Group I patients averaged 21.5º, Group II 24.1º. Coronal curves averaged 60º in Group I immature patients and 52.2º for Group II; mature Group I patients averaged 54.7º and 49.8º for Group II.

Results: Sagittal progression 10º or more, occurred in 6/10 (60%) Group I Risser 0 and 18/56 (32%) Group II Risser 0 patients. In mature (Risser 1-5) patients, there was 10º or more progression 10/37 (27%) Group I patients and 32/144 (22%). The average progression was less in both Groups fused with solid rods, 6.9º in immature and 3.3º in mature patients, as compared to those fused with flexible rods, average 15º both Groups.

Conclusion: Patients who are skeletally immature at surgery were more likely to have progression of their sagittal deformity after anterior fusion; however, solid rod use does appear to decrease incidence and severity. Therefore, scoliosis patients who are skeletally immature and are undergoing anterior spinal fusion with instrumentation should have extra attention given to the sagittal profile both preoperatively and intraoperatively.

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