46 Lumbar Pedicle Fixation 1. Correct spinal deformity. 2. Enhance spinal fusion rates. 3. Facilitate decompression of neural elements. 4. Preserve or enhance lumbar lordosis. 5. Facilitate rehabilitation following surgery. The pedicle is the anchor site of first choice for achieving spinal fixation in the lumbar region. The indications for pedicle fixation include the full spectrum of lumbar spinal disorders requiring spinal stabilization: 1. Spinal instabilities due to lumbar degenerative disorders 2. Spinal instabilities resulting from lumbar decompression procedures 3. Stabilization following corpectomies for tumor 4. Stabilization following anterior discectomies or corpectomies for infection 5. Lumbar scoliosis 6. Lower thoracic or lumbar fractures 7. Spondylolisthesis 8. Lumbar osteotomies 9. Repair of lumbar pseudarthroses 1. Absent, fractured, or atrophic pedicles 2. Severe osteopenia that limits secure screw purchase (insertion torque less than 4.0 inch-lbs) 1. Pedicle fixation provides for rigid segmental immobilization of the spinal column. 2. The pedicle is frequently the only intact anatomic structure that can be used for fixation following a laminectomy. Pedicular fixation permits instrumentation and fusion to be limited to prior surgical levels. 3. Pedicle screws provide excellent fixation without spinal canal encroachment. 4. Pedicle fixation increases the rate of arthrodesis in lumbar fusion procedures. 5. Pedicle screws provide an excellent means for obtaining sacral fixation. 6. Pedicle fixation enhances preservation of sagittal contour. 7. Pedicle fixation minimizes the need for postoperative immobilization. Pedicle fixation procedures are not without disadvantages. Some disadvantages associated with lumbar pedicle procedures include: 1. Increased blood loss 2. Increased operative time 3. Increased risk of postoperative wound infection 4. Implant bulk may cause soft tissue irritation 5. Implant rigidity may lead to transition syndromes as levels above or below the instrumented levels undergo accelerated degenerative changes due to stress transfer 6. Risk of neurologic injury Prior to surgery, the patient’s radiographs (Fig. 46–1) and neurodiagnostic imaging studies [computed tomography (CT), magnetic resonance imaging (MRI)] are reviewed to assess pedicle diameter, length, and orientation. Abnormalities such as pedicle dysplasia or pedicle fracture are identified, and a strategy is developed to achieve optimal spinal fixation in the face of these challenges. Knowledge of normal pedicle anatomy is essential to proper placement of pedicle screws. The pedicles form the superior and inferior boundaries of the intervertebral foramen with the exiting nerve root in close proximity to the inferior medial borders of the pedicle. In the foramen the nerve root lies 0.4 to 0.5 cm superior to the upper border of the caudal pedicle. Avoiding placement of the pedicle screws too inferiorly will protect against injury to the nerve root. The lumbar pedicles are oval in cross section with the medial-lateral width smaller than the sagittal width except at L5. The medial-lateral width determines the maximum allowable screw diameter. There is a decreasing medial-lateral pedicle width from L5 to L1 with the mean of 18 mm at L5 and 10 mm at the L1 pedicle. The mean sagittal width at L1 is 15 mm, diminishing to a mean of 14 mm at L5. The pedicles are directed from a posterolateral to an anteromedial direction. The transverse plane angle between the long axis of the pedicle and the midsagittal line increases from L1 to L5 with a mean of 12 degrees at L1 and 30 degrees at L5. The sagittal pedicle angle is less variable than the transverse angle, with less than a 10-degree difference between L1 and L5. The distance from the anterior cortex of the vertebral body to the posterior entrance point to the pedicle is approximately 50 mm at each lumbar level. The patient is positioned prone on a radiolucent table (e.g., Jackson table). A radiolucent frame facilitates imaging. The abdomen is permitted to hang freely. The hips are extended to enhance lumbar lordosis. A midline posterior approach to the spine is performed with subperiosteal exposure of the posterior bony elements to the level of the transverse processes. Care is taken to preserve the facet joint capsules until the surgical levels to be fused are confirmed either anatomically or with a radiograph. If lumbar decompression is required, screw placement can either precede or follow lumbar decompression based on surgeon preference. Our practice is to place screws prior to performing decompression except in unusual cases such as high-grade spondylolisthesis where partial reduction of L5 will make placement of the L5 pedicle screw easier.
Goals of Surgical Treatment
Indications
Contraindications
Advantages
Disadvantages
Procedure
Preoperative Planning: Review the Anatomy of the Pedicle
Technique
Patient Positioning and Exposure
Pedicle Localization
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