A Comparison between Smith-Petersen Osteotomy and Pedicle Subtraction Osteotomy with an Average 4 years Follow-up.
Bao, Hongda MD/PhD; He, Shouyu Mphil; Liu, Zhen PhD; Zhu, Zezhang PhD; Qiu, Yong MD; Zhu, Feng PhD
Study Design. A retrospective radiographic study.
Objective. To compare compensatory behavior of coronal and sagittal alignment following PSO and SPO for degenerative kyphoscoliosis.
Summary of Background Data. There was a paucity of literature paying attention to the post-operative imbalance after pedicle subtraction osteotomy (PSO) or Smith-Petersen osteotomy (SPO) and natural evolution of the imbalance.
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 pre-operatively, post-operatively and at last follow-up and radiographic parameters were measured. The lower instrumented level (LIV) and level of osteotomy were compared between the patients with and without improvement.
Results. Negative sagittal vertical axis (SVA) was observed in PSO group postoperatively, implying an over-correction of SVA. This negative SVA improved spontaneously during follow-up (P<0.05). Coronal balance was found to worsen immediately post-op in the SPO group (P<0.05). At the last follow-up, spontaneous improvement was observed in 15 patients and the average coronal balance (CB) decreased to 16.35mm. For the 15 patients with improved CB, fusion at L5 or above was more common compared to the 11 patients with persisted post-operative imbalance (P = 0.027), while no difference in term of levels of osteotomy was found (P>0.05).
Conclusion. The over-correction 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 SPO patients.
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