Analysis of Radiographic Parameters Relevant to the Lowest Instrumented Vertebrae and Postoperative Coronal Balance in Lenke 5C Patients

In Brief Study Design. A retrospective radiographic study. Objective. To investigate which preoperative radiographic parameters best correlate with the angulation and translation of the lowest instrumented vertebra (LIV) and global coronal balance after posterior spinal pedicle screw fixation for thoracolumbar/lumbar (TL/L) adolescent idiopathic scoliosis. Summary of Background Data. Lenke 5C patients with a single, structural TL/L curve can be treated by either an anterior or posterior approach. One of the operative goals when treating Lenke 5C patients is to level and center the LIV, thereby achieving a better global coronal balance. To our knowledge, no study has investigated which specific radiographic parameters correlate with these surgical outcomes after posterior pedicle screw fixation. Methods. Twenty-seven patients with TL/L adolescent idiopathic scoliosis were identified in this study, and they underwent posterior fixation and fusion by pedicle screws with a minimum 2-year follow-up. Preoperative and postoperative radiographs were reviewed measuring various radiographic parameters as well as specific measurements related to the LIV. Correlation of these parameters to LIV translation and global and regional coronal balance (C7-central sacral vertical line [CSVL], LIV-CSVL distance) were then evaluated. Results. Four patients demonstrated global coronal imbalance postoperatively by radiographic and clinical evaluation. Regression analysis identified three radiographic parameters that correlated significantly with the postoperative global coronal balance (C7-CSVL): preoperative C7-CSVL (r = 0.44, P = 0.023), preoperative LIV tilt (r = 0.60, P = 0.001), and postoperative LIV tilt (r = 0.65, P = 0.0002). The radiographic parameters that correlated with postoperative LIV-CSVL were: preoperative LIV-CSVL (r = 0.57, P = 0.017), preoperative LIV tilt (r = 0.40, P = 0.04), and postoperative LIV tilt (r = 0.46, P = 0.015). The radiographic parameters correlating to LIV translation were preoperative LIV-CSVL (r = 0.88, P < 0.001) and preoperative C7-CSVL (r = 0.44, P = 0.02). Conclusion. LIV tilt is a very important radiographic parameter that strongly correlates to postoperative global and regional coronal balance. In patients with Lenke 5C curves undergoing posterior spinal fixation using pedicle screw constructs, preoperative LIV tilt equal to or exceeding 25° and failure of postoperative LIV tilt to reduce below 8° correlate with a high risk of developing postoperative global coronal imbalance. This is a retrospective, radiographic study to investigate correlations between preoperative radiographic parameters relevant to the LIV and postoperative coronal balance after posterior spinal pedicle screw fixation in Lenke 5C patients. Our study suggests that the LIV tilt is a very important radiographic parameter correlating strongly with postoperative global and regional coronal balance. Regression analysis indicated that both preoperative and postoperative LIV tilts correlated strongly to the postoperative global coronal balance (C7-CSVL) and regional coronal balance (LIV-CSVL). Patients with Lenke 5C curves whose preoperative LIV tilt equaled or exceeded 25° and whose postoperative LIV tilt failed to reduce below 8° have a high risk of developing postoperative global coronal imbalance after posterior pedicle screw fixation.