Introduction: Sagittal plane alignment has become a primary goal of adult deformity surgery. Recent authors have described the use of preoperative formulas to predict the amount of correction needed during PSO to obtain an appropriate final standing lumbar lordosis. The relationship between the intraoperative lordosis created by an osteotomy and the final standing xrays is unknown. This abstract is the first description of the change in lordosis from a prone intraoperative position to a final standing film in patients undergoing a PSO procedure.

Methods: A total of 13 patients undergoing PSO as part of a fusion were studied. The average age was 67 years. Pre- and post-operative measurements of pelvic tilt, pelvic incidence and lumbar lordosis were performed on standing films. LL was measured on intraoperative films with patients in a prone position after closure of the osteotomy. Standing 36 inch digitized films at 6 weeks postop were used in this analysis.

Results: The preoperative LL was 20° (range 2-50, ± 15). The postoperative LL was 56° (range 26-75, ±13), with an average total correction of 36.8° (p<0.0001, range 20-62, ±13). The intraoperative LL was 68° (range 49-86, ±11). The average change in lumbar lordosis after PSO from intraoperative prone to postoperative standing imaging was -12.1° (p<0.0001, range -24 to 0, ±7).

Conclusions: This study demonstrates that an intraoperative measurement of lordosis created by a pedicle subtraction osteotomy significantly overestimates the final standing lumbar lordosis by greater than 12 degrees. Given the relatively narrow target between the pelvic incidence and lumbar lordosis (±9 degrees) advocated by recent papers, this overestimation could lead to sagittal imbalance and predispose patients to failure. We therefore advocate that spinal deformity centers assess the difference in LL between intraoperative prone films and postoperative standing films in their patients in order to ensure appropriate spinopelvic balance after PSO.

Patient Care: This study will help to prevent undercorrection of lumbar lordosis during pedicle subtraction osteotomy procedures

Learning Objectives: Increase the understanding of intraoperative vs standing sagittal balance

References: Schwab F, Ungar B, Blondel B, Buchowski J, Coe J, Deinlein D, et al.: Scoliosis Research Society—Schwab Adult Spinal Deformity Classification. Spine 37:1077–1082, 2012