Pedicle Subtraction Osteotomy (PSO)
Pedicle Subtraction Osteotomy (PSO) is the surgical resection of a wedge section of the vertebra to provide correction of kyphotic deformities. It is a more radical procedure that involves removal of all the posterior elements (spinous process, lamina, facet joints and pedicles) and a wedge section of the vertebral body. It is performed through a posterior approach and used for spinal deformity correction, especially sagittal malalignment with severe kyphosis. It is a complex, high risk procedure that completely destabilizes the spine (thereby allowing major deformity correction) and requires extensive reconstruction with posterior segmental stabilization and instrumentation.
Who is a candidate for Pedicle Subtraction Osteotomy?
PSO has been used to treat patients with severe kyphotic deformity. It is particularly valuable in patients with sagittal malalignment (kyphosis) that requires substantial correction, especially if the deformity is located in the lumbar spine or anatomy/prior fusion prevents the use of less radical osteotomy procedures (ankylosing spondylitis). PSO allows a large correction of 30-40 degrees at the treated level.
Figure 1 and 2. Illustration demonstrating the bone resected in pedicle subtraction osteotomy (from Medtronics Vertebrectomy Surgical Technique manual)
How is Pedicle Subtraction Osteotomy performed?
PSO was initially described as a treatment for patients with ankylosing spondylitis. It has the advantage of correcting kyphosis without lengthening the anterior column (and potentially stretching and injuring vascular structures). It also avoids the morbidity associated with the anterior approach. The spine is approached posteriorly and pedicle instrumentation placed across the regions necessary for deformity correction and stabilization. The specified vertebra is exposed and the spinous process, lamina, and facets removed. The lamina 1 level above and below are also removed to prevent kinking of the neurologic structures following correction. The pedicles of the involved level are then resected to their base at the posterior vertebra while protecting the exiting nerve roots. A temporary rod is placed for stability prior to resection of the anterior column.
Figure 3 and 4. Resection and osteotomy of the anterior column. The pedicles and posterior wall have been removed and the amount of body needed for correction is resected. (from Medtronics Vertebrectomy Surgical Technique manual)
Subperiosteal dissection of the vertebral body is performed and retractors placed. The amount of bone needed for the planned correction is then removed with osteotomes, curettes, and reamers. Temporary rods are used to stabilize the spine during deformity correction and the dura carefully inspected to ensure no neurologic compression. Neuromonitoring is performed to confirm no new neurologic changes; if stable definitive instrumentation and fusion with bone graft completed. Blood pressure, Hgb level, and oxygenation should be maintained to ensure adequate neurologic perfusion.
Figures 5 and 6. Final reconstruction following kyphosis correction, pedicle instrumentation, and fusion. Vertebrectomy includes resection of the remaining vertebral body including the adjacent disc spaces and placement of anterior cage to maintain column height.
What are the pros and cons of Pedicle Subtraction Osteotomy?
Pedicle subtraction osteotomy provides excellent correction of severe kyphosis but it is a complex spinal reconstruction with significant risks. These include but are not limited to infection, neurologic injury, dural tear, instrumentation failure, non union (pseudo-arthrosis), chronic pain, DVT, PE, chronic pain, and need for revision surgery. Each patient is unique and only a comprehensive evaluation with a fellowship trained spine surgeon can give you the best appreciation of the risks and benefits for surgical treatment of your condition.
