Comparison of Smith-Petersen Osteotomies versus Pedicle Subtraction Osteotomies for the Treatment of Fixed Sagittal Imbalance (71 Patients with Minimum 2-Year Followup)

• a - Medtronic Sofamor Danek

Purpose: Smith-Petersen 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 hypothesis was that when comparing >=3 SPOs to a single PSO, the correction in C7 plumb and lumbar lordosis would be identical in each group, the SPO group would have greater tendencies to decompensation (due to shortening the posterior column/concavity and lengthening the anterior column/convexity in patients with residual lumbar rotation and scoliosis), blood loss would be greater in the PSO group and improvement in Oswestry scores would be identical in each group.

Methods/Demographics: Thirty patients who underwent SPO were compared with 41 patients who underwent PSO (followup 2 to 11.5 years). All patients’ surgeries were performed at one institution between 1985 and 2000. The mean segments of osteotomies in the SPO group were 2.47 (range 1-5 segments). 14 patients in the SPO group had 3 or more osteotomies. All of the PSOs were performed at one segment. The PSO patients were older, (p<.0001) and had more comorbidities (p=.03). Patients were evaluated by preop and ultimate postop standing radiographs and a prospectively collected database and outcomes questionnaires. See table for demographics.

Results: The mean correction of the kyphotic angle at the osteotomy sites for the SPOs were 10.6° per segment. For those with >=3 SPOs, the average total correction was 30.7±7.1°, 31.7±9.1° for the PSO group. However, the improvement in sagittal balance was statistically significantly less with >=3 SPOs (5.5±5.9cm) than PSO (11.2±7.2cm; p<0 .01). Comparing>=3 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 1398±738mL in SPO group (1392±664mL>=3 SPO group), and 2617±1645mL in PSO group (p<.001; p<.01). The total operative time for SPO versus PSO groups was identical. There were no deaths or permanent neurologic deficits in either group. However, there were substantial complications in both groups, 13 of the 30 SPO and 29 of the 41 PSO patients. In the SPO group there was one patient with a nonunion at an osteotomy site; in the PSO group there were two patients with nonunion at an osteotomy site. The mean Oswestry score improved from 42.3±14.2 preoperatively to 21.3±14.8 at the last visit in SPO group and in PSO group, it improved from 47.9±15.8 preoperatively to 29.7±18.3 at the last visit (p=0.35).

Conclusions: When comparing >=3 Smith-Petersen osteotomies (14 patients) to one pedicle subtraction osteotomy (41 patients), the correction in kyphosis is nearly identical, but the improvement in the C7 plumb is significantly better for the PSO group. There is a significantly greater likelihood of decompensating the patient to the concavity with >=3 SPOs than with a single PSO (p<0 .02). Total operative time in the SPO versus PSO groups is identical. However, blood loss substantially greater with group (p<.001).

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