Can we predict the ultimate lumbar curve in adolescent idiopathic scoliosis patients undergoing a selective fusion with undercorrection of the thoracic curve?

Study Design. Retrospective review of anterior and posterior fusions for treatment of adolescent idiopathic thoracic scoliosis. Objectives. To delineate the best factors determining final lumbar curve magnitude in patients with adolescent idiopathic scoliosis undergoing a selective thoracic anterior or posterior spinal fusion at or proximal to the first lumbar vertebra. Summary of Background Data. Although spontaneous lumbar curve correction occurs consistently following a selective thoracic anterior or posterior spinal fusion, the degree of correction is somewhat unpredictable. Methods. One hundred consecutive patients with major thoracic- compensatory lumbar adolescent idiopathic scoliosis treated by a single surgeon with either selective posterior spinal fusion ( n = 44) or anterior spinal fusion ( n = 56) of the main thoracic region with an unfused lumbar spine with a lumbar B modifier ( lumbar apex touching the center sacral vertical line) or lumbar C modifier ( lumbar apex completely lateral to the center sacral vertical line) were retrospectively reviewed. Results. Those patients who maintained excellent postoperative coronal balance, with spontaneous lumbar curve correction, had their thoracic Cobb corrected intraoperatively to a measurement very close to but not more than that of the preoperative thoracic push- prone Cobb. Stepwise multiple linear regression analysis was used to develop a formula to help predict lumbar response in those patients undergoing selective thoracic fusion. This is represented in the following formula: Final lumbar Cobb = 14.4 + 3.06 ( lumbar modifier; 0 = B, 1 = C) + 0.30 ( preoperative standing lumbar Cobb) - 0.18 ( preoperative supine lower Cobb) + 0.81( preoperative push/ prone lumbar Cobb) - 0.15( preoperative standing thoracic Cobb) - 0.16(% thoracic Cobb change from preoperative to immediate postoperative). Final model R-2 = 0.72 Conclusions. Of the preoperative measurements examined, the preoperative push- prone is the best preoperative flexibility radiograph to predict the final lumbar curve measurement and, along with other factors, 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.