Pedicle Subtraction Osteotomy

Courtney W. Brown and Douglas C. Wong

Goals of Surgical Treatment

To achieve sagittal balance of the spine with a single-stage posterior osteotomy where a plumb line from C7 is at or behind the posterior superior edge of the S1 body.

Diagnosis

1. The patients complain of chronic back pain with associated with hamstring tightness. Patients must flex their knees to gaze forward.

2. Physical examination reveals forward flexion of the trunk when the knees are extended. Standing anteroposterior (AP) and lateral x-rays show anterior sagittal imbalance with loss of lumbar lordosis.

3. Plumb line from C7 on the lateral film is anterior to the posterior superior edge of the S1 body.

Indications for Surgery

Loss of lumbar lordosis (flat back) with associated complaints and physical findings as mentioned above.

Contraindications

1. History of ongoing infection from previous surgery

2. Severe osteoporosis, which could lead to implant loosening

Advantages

1. Elimination of the need for multiple posterior osteotomies.

2. Anterior disc space is not opened as a result of the posterior closure of the posterior elements.

3. Elimination of an anterior procedure.

4. Biplanar osteotomy may be performed if coronal decompensation exists.

Disadvantages

1. Coronal decompensation may occur if the osteotomy cuts are not parallel.

2. Blood loss, dural rents, and neurologic compromise.

Procedure

Upright AP and lateral long cassette radiographs are taken to evaluate sagittal and coronal decompensation. With these radiographs, a tracing on clear x-ray film can be cut to determine the size and location of the osteotomy to restore normal sagittal alignment. Spinal fixation points such as hook or pedicle screw sites can be planned. If feasible, the osteotomy should be performed at L2 or below to avoid risk of spinal cord injury. A Carm or computed tomography (CT)-guided navigation (e.g., STEALTH), should be used to assist with placement of pedicle screws and localization of the osteotomy site. Spinal cord monitoring should be used: electromyograms (EMGs) at L2 or caudal and multimodality evoked potentials (MEPs) and somatosensory evoked potentials (SEEPs) above L2. As this operative procedure can involve significant blood loss, three to four units of autologous blood should be collected preoperatively. A cell saver should be used intraoperatively.

Intraoperative

After adequate general endotracheal anesthesia, the patient is placed prone on a four-poster spine frame on an operating room table equipped with an elevating kidney rest. The kidney rest should be at the level of the patients‘ distal thighs or knees (Fig. 50–1). Elevating the kidney rest intraoperatively facilitates closure of the osteotomy site by extending the pelvis through the hips (Fig. 50–2). Another technique involves the use of a bent/flexed operating room table with two separate four-poster spine frames. Straightening the table closes the osteotomy site.

After sterile prep and draping, the spine is exposed through a standard posterior approach. The paraspinous muscles are stripped off the posterior elements or fusion mass out to the transverse processes and deep retractors are placed. If CT-guided navigation is to be used, it is important not to disturb the bony architecture of the fusion mass. This will allow accurate registration. Bovie electrocautery may be used to separate the soft tissue from the fusion mass.

Only gold members can continue reading. Log In or Register to continue