Comparison of Smith-Petersen versus pedicle subtraction osteotomy for the correction of fixed sagittal imbalance

Study Design. Clinical, radiographic, and outcomes assessment comparing two surgical techniques. Clinical data were collected prospectively. The radiographic analysis was done retrospectively. Objectives. Smith-Petersen (chevron type) osteotomy (SPO) and pedicle subtraction osteotomy (PSO) have been used to correct fixed sagittal imbalance. This study compares the results of these two methods. Our hypotheses were that when comparing three or more SPOs to a single PSO, the correction of kyphotic angle at the osteotomy site would be nearly identical in each group, the correction in C7 plumb and lumbar lordosis would be identical, the SPO group would have equal tendencies to decompensation as the PSO group, blood loss would be identical in the two groups, and improvement in Oswestry scores would be identical in each group. Summary of Background Data. Many papers have described the surgical technique and results of SPOs and PSOs. No effort has been made to compare the results of the respective techniques at a single institution. Methods. Thirty patients who underwent SPO were compared with 41 patients who underwent PSO (follow-up, 2-11.5 years). All patients' surgeries were performed at one institution between 1989 and 2001. Fourteen patients in the SPO group had three or more osteotomies. All of the PSOs were performed at one segment. Patients were evaluated by preoperative and ultimate postoperative standing radiographs and a prospectively collected database with outcomes questionnaires. Results. The mean correction of the kyphotic angle at the osteotomy sites for the SPOs was 10.7 degrees per segment. For those with three or more SPOs, the average total correction was 33.0 degrees +/- 9.2 degrees, and 31.7 degrees +/- 9.0 degrees for the PSO group. However, the improvement in sagittal balance was statistically significantly less with three or more SPOs (5.5 +/- 4.5 cm) than with one PSO (11.2 +/- 7.2 cm; P<0.01). Comparing three or more SPOs to one PSO, the SPO group decompensated the patients more substantially to the concavity (P<0.02). The mean estimated blood loss (adding up all anterior and posterior surgeries) for the procedure was 1,398 +/- 738 mL in the SPO group (1,392 +/- 664 mL in the three or more SPO group), and 2,617 +/- 1,645 mL in the PSO group (P<0.001; P<0.01). The mean Oswestry score improved from 42.3 +/- 14.2 before surgery to 21.3 +/- 14.8 at the last visit in the SPO group. In the PSO group, it improved from 47.9 +/- 15.8 before surgery to 29.7 +/- 18.3 at the last visit (P=0.35). Conclusion. When comparing three or more SPOs (14 patients) to one pedicle subtraction procedure (41 patients), the correction in kyphosis was nearly identical. There was a significantly greater likelihood of decompensating the patient to the concavity with three or more SPOs than with a single PSO (P<0.02). The blood loss was substantially greater with the PSO group (P<0.001).