Pedicle Subtraction Osteotomy in Adult Spinal Deformity: Comparing Fixed Versus Flexible Sagittal Imbalance.

ABSTRACT

STUDY DESIGN/SETTING: Level III-retrospective radiologic and clinical comparative study. OBJECTIVE: This study compares the results of pedicle subtraction osteotomy (PSO) for fixed versus flexible sagittal imbalance in adult spinal deformity. SUMMARY OF BACKGROUND DATA The result of PSO may be different according to the flexibility of the deformity. METHODS: Sixty-one patients who underwent PSO were enrolled with a minimum 2-year follow-up. Twenty-one patients had fixed imbalance resulting from ankylosing spondylitis and iatrogenic flatback deformity, and 40 patients had flexible imbalance resulting from degenerative spinal deformity and posttraumatic kyphosis. RESULTS: The mean age was 54.9±9.2 years in the fixed group and 65.9±10.5 years in the flexible group (P<0.01). PSO achieved about 35 degrees of correction of kyphotic angle in both groups, but the loss of correction (LOC) was higher in the flexible group. The correction of Lumbar Lordosis was similar in both groups, at 31.7±15.4 degrees in the fixed group and 32.3±20.8 degrees in the flexible group, although the LOC was also higher in the flexible group than in the fixed group, at 9.8±12.4 and 2.7±3.5 degrees, respectively (P<0.01). The sagittal vertical axis was much more restored in the fixed group than in the flexible group (P=0.002). Postoperative complications were identified in 4 patients in the fixed group, consisting of neurological deficit and screw loosening, and in 15 patients in the flexible group, consisting of proximal junctional kyphosis, screw pullout, rod fracture, and pseudarthrosis. CONCLUSIONS: PSO for flexible sagittal imbalance resulted in a higher LOC of the osteotomy angle, Lumbar Lordosis, and sagittal vertical axis relative to the fixed deformity. Furthermore, more complications such as implant failure developed in the flexible group.