35 Minimally Invasive Laminectomy for Lumbar Stenosis

Lumbar spinal stenosis is the most commonly diagnosed spinal disorder in the elderly population of the United States today. It is a major cause of lower back pain, leg pain, activity limitation, and disability in this population, causing an increasing number of patients to consider surgery. In fact, rates of surgery for lumbar stenosis have increased up to eightfold in recent years.¹ Anatomically, spinal stenosis is defined as a reduced cross-sectional area of the vertebral canal, usually resulting in compression of neural structures. This may occur in the central portion of the spinal canal (termed central stenosis); in the lateral recesses of the canal, between the posterior margin of the vertebral body and the anterior margin of the superior articular process (lateral recess stenosis); or in a combination of both areas. Spinal stenosis may be congenital or acquired. Congenital stenosis, which is usually associated with a shortened pedicle length or hereditary syndromes (i.e., achondroplasia), typically presents at a younger age than acquired or spondylotic spinal stenosis. Congenital stenosis is rarely symptomatic in childhood or young adult life and typically presents in the third or fourth decade as degenerative changes are superimposed. The bone in patients with congenital spinal stenosis tends to be relatively hard, making decompression tedious. Acquired forms of the disease may arise in a developmentally normal canal when degenerative changes occur, hallmarked by facet arthropathy, ligamentous hypertrophy, osteophytic growth, and intervertebral disc bulging. These acquired forms of lumbar spinal stenosis are the most common forms of the condition, most often implicated in cases leading to surgery.^2,3 Canal stenosis may also be secondarily associated with other degenerative conditions, such as spondylolisthesis or scoliosis.

35.2 Evolution of Techniques

The most commonly performed surgical procedure for treating lumbar stenosis, until recently, was an open laminectomy. To perform a standard open laminectomy, resection of the spinous process, the interspinous and supraspinous ligaments, bilateral laminae, the ligamentum flavum, and often varying amounts of the facet complex is required. This method allows complete decompression of the spinal canal, including the lateral recess and intervertebral foramen, but can potentially lead to poor patient outcomes and need for additional surgery for adjacent segment disease (ASD^4,5; Fig. 35.1). This wide resection may be considered excessive for forms of lumbar stenosis occurring solely at the level of the disc space, which occurs in the vast majority of cases. These forms of the disease, mainly caused by intervertebral disc pathology and a combination of thickened ligaments and hypertrophic facets, are accessible through a widened interlaminar space. This knowledge, combined with an effort to preserve midline posterior element structures, led to the introduction of the hemilaminotomy, initially performed bilaterally, to treat degenerative lumbar stenosis.^6,7,8

Fig. 35.1 (a-c) Potential problems with traditional open laminectomy include adjacent segment disease (ASD), which can result in 13% reoperation rate at 4-year follow-up.⁴ The removal of the spinous process can lead to facet hypertrophy causing ASD after multilevel traditional laminectomy, fusion, and instrumentation. This is felt to occur due to stresses placed on the adjacent facet and ligamentum flavum. (Adapted from Perez-Cruet and Mendoza-Torres 2015.⁵)

Young et al⁹ introduced the concept of the unilateral approach for performing a bilateral decompressive laminotomy in which the ipsilateral side of the canal is decompressed first and the contralateral canal, lateral recess, and intervertebral foramen are decompressed under the midline structures. This approach offered the advantage of preserving the spinous processes and midline ligamentous structures and simultaneously allowed the surgeon to access both sides of the spinal canal to address the main points of compression.

With the recent advent of endoscopic and minimally invasive approaches for removal of herniated lumbar discs, it became a natural progression to apply the technique to decompressive laminectomy and laminotomy. In addition to the benefits associated with preserving the midline structures, this new method provided a smaller skin incision, less tissue trauma, and improved visualization. After Guiot et al¹⁰ reported the feasibility of the technique in cadavers, Khoo and Fessler¹¹ later demonstrated that it was a safe, effective surgical procedure for the decompression of the stenotic lumbar spine.

35.3 Indications and Contraindications

35.3.1 Patient Selection

With the increasing incidence of lumbar stenosis, appropriate patient selection for the minimally invasive approach becomes the first essential step toward a good outcome. Reoperative cases are relatively more difficult and should not be attempted until the surgeon has gained a great deal of experience with minimally invasive approaches. Morbid obesity increases the working distance from the skin to the spine and increases the technical difficulty for the surgeon. These cases are best deferred until a high level of experience and comfort with tubular retractor systems is achieved.

35.3.2 Preoperative Planning

Patients presenting with lumbar stenosis characteristically complain of bilateral or unilateral leg pain, weakness, and/or paresthesias. Many patients (~50%) also suffer from neurogenic claudication, a type of leg pain that is typically aggravated by standing and walking and relieved by sitting or lying down.^1,3 Symptomatic relief with lumbar flexion is often a reliable characteristic that helps distinguish so-called neurogenic spinal claudication from vascular claudication (caused by arterial insufficiency). The bicycle test, in which the patient is leaning over riding a stationary bike, can also help distinguish the two forms. Patients with neurogenic claudication can ride without pain because they are in a flexed position, which helps open the spinal canal and relieve symptoms, whereas those with vascular claudication will reproduce their pain symptoms. The neurologic examination at rest may be fairly benign until very late stages of the disease when fixed motor or sensory deficits become evident. Sphincter disturbance is a late symptom of the condition and is usually associated with severe compression of the cauda equina, which is sometimes the result of an acute disc herniation superimposed on preexisting spinal stenosis.

35.3.3 Radiographic Workup

Radiographic imaging usually begins with plain films, which often reveal degeneration of the motion segments, loss of disc space height, narrowed neural foramina, and hypertrophy of the facet joints. MRI scanning is the study of choice and will, with rare exception, provide diagnostic images. Typical findings include degenerative disc disease, ligamentous and facet hypertrophy, and a triangularly shaped trefoil spinal canal ( Fig. 35.2).

Additionally, spinal stenosis occurs at the level of the disc space; therefore, focused surgical treatment can help preserve those anatomical structures not causing neural compression. For the occasional patient who is not a candidate or is uncomfortable with an MRI, myelography combined with a CT scan can be obtained. Myelography will show constrictions or blocks in the dye column, and the CT scan can be used for accurate measurements of canal diameter. The CT/myelogram study is especially helpful in identifying lumbar stenosis in those patients having undergone previous instrumented fusion surgery as the artifact created by the hardware prevents adequate canal visualization using MRI ( Fig. 35.3). Lumbar stenosis occurs at the level of the disc space and is caused in most situations from a combination of facet and ligamentum flavum hypertrophy. Thus, focused minimally invasive laminectomy can achieve adequate neural decompression while preserving much of the supporting anatomy of the spine ( Fig. 35.4).

Fig. 35.2 Preoperative MRI showing triangularly shaped “trefoil” canal caused by hypertrophy of the ligamentum flavum and facet complex.

Fig. 35.3 (a–c) Adjacent segment disease (ASD) after open laminectomy, fusion, and instrumentation. Note facet hypertrophy and stenosis seen on sagittal and axial CT requiring reoperation.

Following minimally invasive laminectomy, postoperative MRI shows adequate healing of the paramuscular muscle afforded by the muscle-dilating approach with adequate decompression of the spinal canal. We have noted that there is minimal scar formation, which may ultimately improve patient outcomes ( Fig. 35.5).

35.3.4 Operative Setup and Instrumentation

Minimally invasive lumbar laminectomy is performed in a standard operating room with routinely available equipment. Fluoroscopy is used for the initial approach and confirmation of the correct surgical level. The procedure can be performed using a series of muscle dilators to approach the spine over which a tubular retractor is placed and is marketed by several different manufacturers. Recent developments like the Thompson MIS One-Step-Dilator (Thompson MIS, Salem, NH), eliminate the need for multiple muscle dilators and thus facilitate the procedure and reduce the risk of passing a dilator into the canal ( Fig. 35.6). Muscle damage and dissection are minimized. The tubular retractors are available in several working diameters and in various lengths to accommodate variability in the depth of soft tissues. Standard spinal surgery instruments are not ideal for use with tubular retractor systems because of the confined space of the retractors. If the surgeon is using a microscope for magnification and illumination, either the surgeon’s hands or the back of the instrument tends to obscure the visual pathway. If an endoscope is used, then the tube tends to become clogged with the scope, suction, and instrument. For these reasons, a full set of bayonetted instruments, including Kerrison rongeurs, curettes, probes, and dissectors, is essential for adequate visualization during the surgery. A long tapered drill facilitates bony decompression ( Fig. 35.6).

The operative microscope is employed for excellent illumination and stereoscopic visualization through the dilated working channel. Surgeons using the operative microscope accomplish this by altering the angle of the working retractor (i.e., tilt the operative table slightly away from the surgeon when performing the contralateral decompression to undercut the spinous process and contralateral lamina). The microscope technique allows for excellent three-dimensional (3D) visualization of the operative anatomy ( Fig. 35.7).

Lumbar Facet Anatomy to Determine Surgical Approach

Lumbar facet anatomy can play an important role in determining spinal stability and whether decompression alone versus decompression and more extensive instrumented fusion is necessary. Anatomical changes in the facet may represent the consequences of spinal instability not detected or appreciated on dynamic plain radiographs. The facet joint, with opposing cartilaginous surfaces, facilitates low friction movement between adjacent vertebral bodies. Together with the disc, the bilateral facet joints transfer loads, and guide and constrain motions in the spine due to their geometry and mechanical function. The facet joints may account for 15 to 40% of low back pain.⁵ However, there are few studies illustrating how morphometric analysis of the facet can help determine the most favorable surgical approach.⁵ We conducted an analysis of facet morphology in the following study to determine the relationship between surgical approach and preoperative facet anatomy visualized on axial MRI images.

Methods

Twenty patients having undergone minimally invasive decompression with or without instrumentation for stenosis were retrospectively analyzed. Morphometric analysis of the lumbar facets at the index level was analyzed in the preoperative lumbar MRI at the mid-disc space level using a longitudinal measurement of the superior and inferior facets¹² ( Fig. 35.8, Fig. 35.9, Fig. 35.10, and Table 35.1).

Fig. 35.4 Lumbar stenosis occurring at the (a) level of the disc space (L2–L3, L3–L4, and L4–L5 levels in this patient) and primarily caused by hypertrophy of the ligamentum flavum and facet joint as seen here at the corresponding axial MRI of (b) L2–L3, (c) L3–L4, and (d) L4–L5 levels. Minimally invasive laminectomy provides focused decompression at the level of compression as seen in these immediate postoperative corresponding (e) sagittal, (f) L2–L3 level, (g) L3–L4 level, (h) L4–L5 level axial, and (i–k) coronal postoperative reconstructive CT images showing minimally invasive laminotomy with autologous morselized bone graft laminar reconstruction and in situ facet fusion.

Preoperative inspection of the MRI can help determine whether minimally invasive laminectomy alone or a more extensive procedure such as decompression with instrumented fusion is necessary (i.e., minimally invasive transforaminal lumbar interbody fusion and percutaneous pedicle screw fixation [MITLIF]^12,13; see Fig. 35.9, Fig. 35.10, Fig. 35.11, Fig. 35.12, Fig. 35.13).

Those patients who underwent decompression alone had an average longitudinal facet morphology of 11.1-mm length of the superior facet of inferior vertebral body and 16.3-mm length of the inferior facet of the superior vertebral body. This compared with an average longitudinal facet morphology in spondylolisthesis patients of 24.7-mm length of the superior facet of inferior vertebral body and 30-mm length of the inferior facet of superior vertebral body. Patients with spinal stenosis and elongation of facets underwent MITLIF, whereas those patients with stenosis and relatively normal facet ratios underwent decompression alone. Therefore, facet morphology may be an important preoperative analysis to determine the need for decompression alone versus more extensive decompression, fusion, and spinal instrumentation.

Fig. 35.5 Twelve-month (a) postoperative sagittal MRI in a patient having undergone right (b) L3–L4 and (c) L4–L5 minimally invasive laminectomy for stenosis with biological laminar reconstruction using morselized autograft. Note preservation of paraspinal muscular anatomy, spinous process, laminar reconstruction, and normal anatomic distribution of cauda equina nerve roots with adequate canal decompression and minimal scar formation.

Traditional surgical treatment for lumbar stenosis includes detachment of paraspinal musculature from midline boney anatomy and removal of the spinous process and lamina bilaterally to achieve decompression. This can potentially increase the incidence of adjacent-level pathology (ALP) and need for reoperation (see Fig. 35.1, Fig. 35.3). A study was conducted to evaluate whether minimally invasive laminectomy and in situ posterior fusion (MIL-ISF) can improve patient outcomes while reducing ALP and need for reoperation.

35.4.1 Methods

Between April 2009 and September 2013, 280 MIL-ISF of the facets using local autograft ( Fig. 35.14, Fig. 35.15) were performed in 155 consecutive patients for lumbar spinal stenosis refractory to nonoperative treatments.⁵ Charts were reviewed retrospectively and outcome scales (Oswestry Disability Index [ODI] and Visual Analogue Scale [VAS]) were answered prospectively preoperatively and over a 5-year follow-up period. Facet anatomy was documented as well as stability seen on preoperative dynamic plain films. Complication and reoperation rates were analyzed.⁵

Results

Patients (n = 155) were followed over a 5-year period with an average 2.3-year follow-up. MIL-ISF was most commonly performed at the L3–L4 (n = 123, 44%) and L4–L5 (n = 98, 35%) levels. Complications occurred in nine (5.8%) cases and included superficial wound infection (n = 2, 1.3%) and pulmonary embolism (n = 1, 0.6%). Additional transient complications included urinary retention and atelectasis. Reoperation occurred in five (3.2%) cases due to new-onset or persistent symptoms with four (2.6%) cases requiring the same level surgery and one (0.6%) case adjacent segment surgery. VAS scores improved from 6.5 to 2.4 (p> 0.001) and ODI improved from 58 to 19 (p> 0.001). Preoperative facet anatomy and plain films determined optimal candidates.

Related posts:

Establishing Ancillary Services and Health Care Regulatory Implications Establishing an Ambulatory Spine Surgery Center Posterior Thoracic Microdiscectomy Posterior Cervical Approach Computer Navigational Guidance in Spine Surgery Minimally Invasive Treatment of Thoracic and Thoracolumbar Idiopathic Scoliosis

Stay updated, free articles. Join our Telegram channel

Join