22 Posterior Lumbar Laminectomy and Pedicle Screw Instrumentation

10.1055/b-0040-174145

22 Posterior Lumbar Laminectomy and Pedicle Screw Instrumentation

Alim F Ramji and Sean M. Esmende

Summary

Degenerative changes in the lumbar spine may involve the vertebral discs, facet joints, and ligamentum flavum and can cause significant morbidity in a certain subset of patients. Instability or spondylolisthesis may also be present which can worsen symptoms. Patient complaints can range from isolated nerve root radiculopathy to frank global stenosis causing difficulty ambulating, claudication, and even bowel/bladder dysfunction. In patients with pathology recalcitrant to conservative treatment or continues to progress, posterior lumbar laminectomy/decompression with pedicle screw instrumentation has become the standard of care. This chapter organizes this surgical treatment into approach and instrumentation segments.

22.1 Introduction

Lumbar spinal stenosis is a common condition that is characterized by degenerative changes in the vertebral discs, facet joints, and ligamentum flavum that effectively lead to foraminal and central canal narrowing. ¹ It affects patients primarily in their seventh decade of life and is among the most common reasons to undergo spine surgery in this age group. ¹ ^, ² The pain and disability caused by this condition can be life-altering. While conservative measures are usually attempted first to treat symptoms, patients with clinical worsening, signs of motor weakness, bowel or bladder incontinence, or exhibiting other manifestations of acute cauda equina syndrome should be managed with a surgical decompression and fusion. ³

The traditional approach to central spinal stenosis is a total laminectomy with preservation of the bilateral pars interarticularis. For the compression of a single nerve root in the lateral recess or foramen, another option is to perform a unilateral interlaminar hemilaminotomy.

22.2 Preop

Surgical table. Radiolucent flat table
Following the induction of general anesthesia, the patient is positioned prone and all bony prominences are well padded. Ensure that there is no pressure on the eyes and nose and the abdomen is hanging free. Somatosensory/motor evoked potential monitoring probes should also be situated by trained neuromonitoring personnel.
Preoperative images should be made easily accessible, including any relevant dynamic radiographs showing sites of instability.
Surgical prepping and draping should be done as per institutional and surgeon guidelines.

22.3 Procedure

22.3.1 Part I: Decompression

A precise midline incision is made directly over the spinous processes. If a total laminectomy is planned, the fascia is carefully dissected bilaterally.
Operative levels are identified using a combination of bony landmark palpation and fluoroscopic imaging (▶Fig. 22.1). Preoperative MRI and radiographs should be correlated with intraoperative imaging to provide more certain localization.
Once levels are confirmed, a longitudinal midline incision is made following the bony prominences of the spinous processes. The skin incision should be straight despite any underlying scoliosis that may cause a shift in the spinous processes. Cautery is used to control any bleeding from the underlying tissues.
Once the spinous processes are visualized, dissection is continued bilaterally toward the facet joint via a subperiosteal plane removing the paraspinal musculature from the lamina. This maneuver limits muscle trauma and reduces the risk of devascularization. Self-retaining retractors are commonly used to aid in dissection and blunt instruments, such as the Cobb, may make this step easier.
Once facet joints are palpated, the dissection is generally carried out laterally to expose portions of the transverse processes, as these will ultimately form the fusion bed. Care should be taken to not destabilize the facet joints. Fluoroscopic imaging can be utilized to confirm adequate location.
The spinous processes are then removed using a rongeur and bone wax is used to limit bleeding. A window into the interlaminar space is created. Blunt instruments, such a curette, are used to negotiate any adhesions between the lamina and underlying ligamentum flavum. The lamina can then be removed using specialized instruments, such a Kerrison rongeur or a high-speed burr. A high-speed burr can be used to create bilateral troughs at the medial margin of the facets. At the superior part third of the lamina, it is best to use the drill only to thin down the ventral cortex, to prevent any dural tears. A Woodson retractor is commonly used to provide gentle downward pressure on the underlying neural elements, to reduce the risk of iatrogenic injury. This is an important step because the dura may be adherent to the ligamentum flavum.
The laminectomy is started at the lower margin of the lamina. A series of 3 and 4-mm Kerrison rogeurs are used to perform the laminectomy in a caudal to cephalad manner. The surgeon may choose to use a cotonoid underneath the lamina, while using the Kerrison to ensure that there is no side biting of the dura, causing an incidental durotomy.
Once the lamina is unroofed, any pathologic thickening of the ligamentum flavum can be removed. The cauda equina should be easily visualized.
Now, the medial third of the facet can be removed with a Kerrison rogeur. It is important note go too far lateral into the facet joint line. Removal of more than a medial third of the facet is rarely required.
A foramintomy is then completed by removing the cephalad aspect of the superior facet, allowing each nerve root to exit freely.
Exiting nerve roots and their respective foramina are inspected and any sites of compression should be removed.
At times, the dura can be very adherent to the bone and ligamentum flavum in the lateral recess due to chronic compression. A visible plane of dissection can be achieved by carefully dissecting above and below the nerve root and slowly liberating the nerve root completely.
It should be emphasized that decompression should be done carefully and meticulously. Anatomic variations and adherent tissue should be expected. If an incidental durotomy is encountered, it should be repaired immediately.
Epidural bleeding should be controlled with bipolar coagulation, gel foam, and cotonoids. Using bone wax on the bleed, bone edges may also be required to limit blood loss and enhance the visualization of the laminectomy field.