Pedicle subtraction osteotomy (PSO) was originally performed in cases of ankylosing spondylitis. This procedure was invented because it was safer than trying to lengthen the anterior column via osteoclasis, which risked vascular injury and death1-4. PSO involves the removal of the posterior elements and the use of a vertebral body wedge to shorten the spine posteriorly and achieve sagittal-plane correction5,6. PSO has been used to correct sagittal-plane deformities not only in patients with ankylosing spondylitis but also in those with degenerative conditions or those who have previously undergone surgical procedures resulting in a loss of lumbar lordosis7,8.
The fixation points are placed with pedicle screws above and below the planned osteotomy level. The posterior elements are decompressed at the level of the osteotomy and at 1 level proximally. In addition to the use of straight and angled curets, a high-speed burr is used to decancellate the vertebral body. Pedicle osteotomes are used to remove the pedicle. Temporary rods are placed. The posterior wall of the body is then impacted into the vertebral body, and the temporary rods are loosened. To close the osteotomy, the bed is extended or the spine is pushed manually, resulting in correction of the lordosis. The temporary rods are tightened. The main rods, independent of the short rods, are used to connect multiple segments several levels above and below the osteotomy site to provide final stabilization.
The alternatives to PSO depend on the surgical history of the patients, as well as the flexibility and alignment of the spine. In a spine with mobile disc spaces, Smith-Petersen osteotomies can be performed posteriorly to shorten the posterior column over multiple segments to gain lordosis. A formal anterior or lateral approach can be performed to release the disc spaces and restore the disc height. A posterior release through the facet joints with segmental compression can achieve desired lumbar lordosis. A vertebral column resection can also be performed to achieve lordosis.
PSO is ideal for patients who have undergone multiple spinal fusions and who have a very rigid, flat lumbar spine. A single posterior approach can be used to provide adequate correction of the flat lumbar spine up to 40°. Asymmetric PSO can also be performed to allow for correction in the coronal plane. Recently, PSO has been performed more frequently because of the improved osteotomy instrumentation, exposure to resection techniques, and improved positioning tables that allow correction of the osteotomy.