Will Immediate Postoperative Imbalance Improve in Patients with Thoracolumbar/Lumbar Degenerative Kyphoscoliosis? A Comparison between Smith–Petersen Osteotomy and Pedicle Subtraction Osteotomy with an Average 4 Years' Follow-Up

There was a paucity of literature paying attention to the postoperative imbalance after pedicle subtraction osteotomy (PSO) or Smith–Petersen osteotomy (SPO) and natural evolution of the imbalance. This study aims to compare compensatory behavior of coronal and sagittal alignment following PSO and SPO for degenerative kyphoscoliosis.Patients and Methods A retrospective study was performed on 68 consecutive patients with degenerative kyphoscoliosis treated by lumbar PSO (25 patients) or SPO (43 patients) procedures at a single institution. Long-cassette standing radiographs were taken preoperatively, postoperatively, and at last, follow-up and radiographic parameters were measured. The LIV and level of osteotomy were compared between the patients with and without improvement.Results Negative SVA was observed in PSO group postoperatively, implying an overcorrection of SVA. This negative SVA improved spontaneously during follow-up ( p   0.05).Conclusion The overcorrection of SVA is more often seen in PSO group. The coronal imbalance is more likely to occur in SPO group. The postoperative sagittal imbalance often spontaneously improves with time. LIV at S1 or with pelvic fixation should be regarded as potential risk factors for persistent coronal imbalance in patients with SPO.