Can We Predict the Ultimate Lumbar Curve in Adolescent Idiopathic Scoliosis Patients Undergoing a Selective Thoracic Fusion?

Introduction: Although spontaneous lumbar curve correction occurs consistently following a selective thoracic anterior spinal fusion (ASF) or posterior spinal fusion (PSF), the degree of correction is somewhat unpredictable.

Purpose: To delineate the best preoperative radiographic correlate of postoperative lumbar curve response in adolescent idiopathic scoliosis patients undergoing a selective thoracic ASF or PSF at L1 or above.

Methods: 100 consecutive patients treated by a single surgeon with either selective PSF (n=44) or ASF (n=56) of the mean thoracic region with an unfused lumbar spine with a lumbar B modifier (lumbar apex touching the central sacral vertical line (CSVL) or lumbar C modifier (lumbar apex completely lateral to the CSVL) were retrospectively reviewed. Pre-op upright AP, supine, push/prone (P/P), right and left side bending (sb) radiographs, early (6 weeks) and a minimum 2 year follow-up radiographs were reviewed obtaining thoracic and lumbar cobb measurements. Statistical analysis was performed to identify the best preoperative radiographic correlate of ultimate lumbar spine positioning and correction.

Results: There was a strong association (p < 0.001) between all obtained pre-op lumbar cobb measurements and the final post-op lumbar cobb measurement. Pearson correlations ranged from 0.38 (sb lumbar cobb measurement) to 0.63 (pre-op upright AP cobb measurement). When trying to predict ultimate lumbar spine position using all available pre-op measures in a multiple linear regression model, upright AP lumbar cobb (p<0.0001) and PP lumbar cobb (p <= 0.03) were the only pre-op measures assistive in predicting final lumbar cobb measurement. These two pre-op measures account for 38% of the variability in the final lumbar cobb measurements. Pre-op supine and side bending measurements did not provide any unique information for the prediction final lumbar cobb measurement.

Conclusion: Of the pre-op measurements examined, the pre-op push/prone is the best preoperative flexibility radiograph to predict the final lumbar cure measurement, and along with the pre-op standing AP radiograph can be used to formulate a model that will help the treating surgeon more confidently predict the final lumbar curve response in patients undergoing a selective thoracic fusion.