Pedicle subtraction osteotomy is a three-column spinal osteotomy involving wedge resection of vertebral body, pedicles, and posterior elements through a single fused vertebra to correct severe sagittal imbalance refractory to less invasive techniques. It is most commonly performed at L3 or L4 to restore lumbar lordosis in patients with flat back syndrome from prior Harrington rod fusion, fixed sagittal imbalance from ankylosing spondylitis, post-traumatic kyphosis, and degenerative or iatrogenic flatback deformity. Compared with Smith-Petersen osteotomy (10-15 degrees) and vertebral column resection (more aggressive but higher morbidity), PSO provides 25-30 degrees of correction per level with single-column shortening.
Indications include sagittal vertical axis greater than 5 cm despite optimization, pelvic incidence-lumbar lordosis mismatch greater than 10-15 degrees, failed posterior column osteotomies, and rigid kyphosis. Comprehensive preoperative planning includes full-length standing radiographs to measure sagittal vertical axis, pelvic incidence, lumbar lordosis, thoracic kyphosis, and pelvic tilt; CT for bone quality and prior fusion mass assessment; and MRI for neural element evaluation. Bone density optimization with bisphosphonates or teriparatide reduces hardware failure risk in osteoporotic patients.
The procedure is performed in prone position through a posterior midline approach with bilateral pedicle screw instrumentation typically extending several levels above and below the osteotomy. The pedicles, posterior elements, and a wedge of vertebral body are removed using a combination of high-speed burr, osteotomes, and curettes while protecting the spinal cord and nerve roots. After bone removal, controlled compression closes the osteotomy and corrects the deformity. Intraoperative neurophysiologic monitoring (SSEP, MEP) is mandatory. Major complications include neurologic injury (3-15%), proximal junctional kyphosis or failure (15-30%), pseudarthrosis, hardware failure, blood loss often exceeding 1500 mL, dural tear, and surgical site infection. Postoperative care emphasizes early mobilization, pain control, prevention of proximal junctional issues, and long-term radiographic surveillance. Functional outcomes are favorable in well-selected patients, with significant improvements in pain, function, and quality of life.