Is Lumbar Stenosis Best Treated with an Open Laminectomy?

2 Is Lumbar Stenosis Best Treated with an Open Laminectomy?

MIS: Hasan R. Syed and Sylvain Palmer
Open: Jonathan M. Karnes and Scott D. Daffner

2.1 Introduction

Lumbar spinal stenosis is defined as any condition that leads to narrowing of the lumbar spinal canal and exiting nerve roots. It can be divided into congenital, acquired, iatrogenic, spondylotic, and posttraumatic stenosis, as defined by Arnoldi et al and modified by Katz and Harris.1,2 Lumbar stenosis is a chronic debilitating condition that affects 5 out of 1,000 Americans older than 50 years. The most common pathophysiology results from degenerative arthritic changes in relatively mobile segments combined with axial loading. These changes include a combination of hypertrophied facet joints and ligaments, osteophyte overgrowth, disc herniation, and spondylolisthesis that can lead to decreased diameter of the spinal canal and subsequent symptoms as a result of neurologic compression and/or mechanical pain.³ Prospective, randomized clinical trials have shown significantly greater improvements in patient’s functional outcome and quality of life with surgical intervention compared to medical management.^4,5,6

Surgical decompression of lumbar stenosis is the most common surgery for patients older than 65 years.⁵ The initial description of the surgical treatment of spinal stenosis was by Sachs and Fraenkel in 1900.⁷ Bailey and Casamajor in 1911 published work linking the findings of osteoarthritis of the lumbar spine with compression of the spinal cord and nerve roots.⁸ Lumbar stenosis has traditionally been treated with an open, decompressive laminectomy, including partial facetectomy and foraminotomies with or without fusion.^5,9 While this is an effective treatment strategy, open decompression (OD) is associated with disruption of normal anatomic support structures and muscle atrophy that can theoretically lead to iatrogenic instability.^10,11

Adams and Hutton showed that the tendency toward anterolisthesis is resisted by multiple spinal elements. The facet joints have been shown to resist 33% of shear forces, with the disc resisting 67%.¹² The supraspinous and interspinous ligaments resist 19% of flexion forces, with the facet capsular ligaments resisting 39% and the disc resisting 29%.^12,13 The force exerted on the spine in physiologic flexion by the trunk is more than double that required to injure the facet joints, and these articulating structures would fail if unaided by other supporting tissues.^12,13 The supraspinous/intraspinous ligamentous complex has the greatest mechanical advantage, being furthest from the axis of rotation. Cusick et al designed a biomechanical study of sequential sectioning of the posterior ligaments and facets using a two-motion segment model.¹⁴ They found that the complex was stable until the supraspinous/interspinous ligaments and associated residual tendinous, midline muscle, and fascial attachments were violated.^12,13,14

Subsequently, minimally invasive spine surgery was developed to address the diseased structures while minimizing the disruption of normal anatomic structures. Muscle-splitting serial tubular dilators and retractors were designed to access the spinal pathology without stripping, devascularizing, or denervating paraspinal musculature and preserving ligamentous and bony anatomy. Decompression can take place with the assistance of endoscopic or microscopic visualization. Interest in less invasive options has led to direct decompressions with bilateral laminotomies and foraminotomies^15,16,17 or unilateral approaches to bilateral decompression.^{16,18,19,20,21} As with any new surgical technique, minimally invasive spine surgery is associated with an initial learning curve.

2.2 Indications for Minimally Invasive Surgery

Minimally invasive surgery (MIS) is generally indicated for the treatment of degenerative spinal stenosis involving any lumbar level as a result of bulging of the intervertebral discs, hypertrophy of the facet joints, and thickening or buckling of the ligamentum flavum. The clinical symptoms of this condition consist of mechanical back pain and radicular pain, as well as classic neurogenic claudication, leading to uni- or bilateral symptoms of the legs. Patients with spinal claudication complain of weakness or heaviness in the lower extremities, with variable sensory deficits or paresthesias when standing and walking. The pain commonly progresses from proximal to distal and is improved by spinal flexion with leaning forward or sitting. Spinal claudication can also be associated with radicular symptoms produced by direct nerve compression that is localized to a particular dermatomal level. A component of mechanical back pain is also commonly present.

There are no absolute contraindications for the use of MIS in the approach to lumbar decompression. Relative contraindications include multiple levels of spinal disease requiring treatment, though surgical time in multiple levels decreases with experience. In addition, exposures deeper than 9 cm (maximum standard retractor depth) and distorted anatomic landmarks, such as those found with reoperation or deformity, are challenging candidates for the minimally invasive approach and are best reserved for the seasoned MIS surgeon.

2.3 Advantages of Minimally Invasive Surgery

The MIS technique utilizes a tubular or bladed retractor system to provide a working corridor for decompression of the neural elements. This approach utilizes “muscle-splitting” dilators and retractors that are designed to minimize disruption of normal anatomy. This leads to decreased trauma to paravertebral musculature on the ipsilateral side and no trauma to the musculature on the contralateral side. In addition, decompression via MIS completely preserves the posterior tension band and spares bony elements, particularly the contralateral lamina and facet joint, as compared to open surgery (OS). Finally, bilateral decompression of the spinal canal can be performed through a unilateral approach by rotating the patient table and angling the approach to optimize the surgeon’s line of sight.

The theoretical advantages of an MIS approach to lumbar decompression include a quicker recovery, short hospital stay, decreased blood loss, and preservation of midline structural elements.22 While OS has demonstrated excellent clinical results, the risk of iatrogenic instability and poor outcome exists.^23,24 In those patients in whom instability is of concern or in those with preexisting spondylolisthesis, or scoliosis with primarily lower extremity symptom, MIS may be an attractive option and has the advantage of preserving posterior stabilizing structures. MIS has also shown advantages in the obese and elderly patient populations, owing to the minimally disruptive nature of the approach and the preservation of normal anatomy.^25,26

2.4 Indications for Open Surgery

The indications for open surgical management of lumbar stenosis are to primarily relieve symptoms of neurogenic claudication or radiculopathy that are resistant to nonoperative therapy.27 The patient-reported history and symptoms, clinical examination, and advanced imaging studies must be consistent with lumbar stenosis in order to expect good results from the surgery. Surgical intervention is indicated when the patient has failed an extended period of appropriate nonoperative treatment and continues to have severe, life-altering symptoms attributable to lumbar stenosis. Open surgical decompression using laminectomy with or without foramenotomy for lumbar stenosis has been the most commonly used operative strategy.

2.5 Advantages of Open Surgery

Lumbar stenosis is most commonly found in elderly patients who develop age-related constriction of the lumbar spinal canal from hypertrophy and distortion of the ligamentum flavum and facet joints as well as posterior displacement of the intervertebral disc. Less commonly, sagittal imbalance and segmental instability can create spinal canal constriction and create or amplify lumbar stenosis. OD provides several advantages. First, it utilizes a standard posterior lumbar approach, which is familiar to all spine surgeons. Consequently, it is less technically demanding. In addition, OD allows direct visualization of the neural elements while performing the decompression and provides more space for placement of surgical instruments. Lastly, in patients presenting with spinal stenosis with a component of vertebral instability or malalignment, OS may provide the additional benefit of facilitating more complex reconstructive techniques.

2.6 Case Illustration

The patient is a 68-year-old man with a long-standing history of intermittent back pain, which he has managed well with over-the-counter nonsteroidal anti-inflammatory drugs. Six months ago, he began developing pain radiating from his back to his right lower extremity, which is worse with standing or walking. His symptoms are relieved after sitting for a few minutes, and he notes he must lean on a shopping cart to make it through the market.

His past history is significant only for hypertension. Medications include baby aspirin, blood pressure medications, and diclofenac. He is a nonsmoker. Outcomes measures obtained at his initial visit include an Oswestry Disability Index (ODI) score of 42, with average visual analog scale (VAS) pain score for the past 24 hours of 6 for back pain and 9 for leg pain.

Physical examination is notable for limited lumbar range of motion on flexion, with some palpable back spasm. Motor strength is 5/5 in his bilateral lower extremities, sensation of light touch is intact, and deep tendon reflexes are 2 + symmetrically. Distal pulses are palpable.

Plain radiographs ( Fig. 2.1) demonstrate mild degenerative disc space loss of height and well-maintained overall alignment, with no evidence of spondylolisthesis on flexion/extension images. His MRI ( Fig. 2.2) demonstrates moderate to severe central and bilateral lateral recess stenosis at L4–L5 due to degenerative disc bulge, facet hypertrophy, and ligamentum flavum hypertrophy.

Since his symptoms became worse, he has been taking diclofenac twice daily. He has tried 6 weeks of physical therapy. An L4–L5 epidural injection provided 3 weeks of excellent relief before symptoms returned. He continues to have significant discomfort and is interested in surgical treatment.

2.7 Surgical Technique in Minimally Invasive Surgery

The patient is brought into the operating room, and most commonly general endotracheal anesthesia is obtained, although it can also be performed under spinal or local anesthesia. A Foley catheter can be placed at the discretion of the surgeon for longer cases, usually two or more levels. The procedure has been described previously 21 and is a modification of the microendoscopic discectomy detailed by Foley and Smith.²⁸ The patient is positioned prone, or lateral, and the level of interest is localized with fluoroscopy. The patient is prepped and draped and the skin is infiltrated with a local anesthetic. A paramedian incision is planned just lateral to the spinous process on the more symptomatic side. Fluoroscopy is utilized to localize the level of the disc space by placing a 22-G spinal needle. If there is a collapsed disc space, then the upper end plate of the lower vertebral body is the target because of the resulting low-lying lamina. Ideally, the inferior laminar edge is in the middle of the exposed field. The direction of approach can be modified in all directions by angling or “wanding” of the retractor to bring the intended structures into view.

When using a tubular system, a 20-mm incision is made, exposing the fascial layer above the paraspinal muscles. A scalpel or unipolar electrocautery is used to incise the fascial layer. The paraspinal muscles are sequentially dilated using tubular dilators, followed by placement of an 18-mm working channel of the shortest length that allows adequate depth of access (usually 50–70 mm). The level of interest and depth of the working channel is confirmed using fluoroscopy. The operative microscope is then moved into the field or an endoscope can be attached. Bovie electrocautery is used to expose and identify the laminar edge. A laminotomy is performed using a combination of diamond burr, Kerrison punches, and curettes. The laminotomy is extended cephalad to above the insertion of the ligamentum flavum on the inferior surface of the superior lamina (to ensure complete resection of ligamentous compressive elements) and caudally to include a smaller portion of the superior aspect of the inferior lamina exposing the pedicle. Partial resection of the medial facet complex is performed as necessary to adequately decompress the lateral recess and the neural foramina.

Fig. 2.1 (a) Anteroposterior, (b) lateral flexion, and (c) extension radiographs of a 68-year-old man with back and leg pain.

Fig. 2.2 (a) T2-weighted sagittal and (b) axial MRI images of the patient in Fig. 2.1 demonstrating moderate to severe central and bilateral lateral recess stenosis at L4–L5.

The working channel is then angled medially, exposing the anterior aspect of the spinous process, which is then removed utilizing a diamond burr. This exposes the lateral recess on the contralateral side where residual lamina, ligamentum flavum, and medial facet can be resected as needed for neural decompression. The angle of approach is the same as that commonly taken during an open laminectomy, making the anatomy familiar to most spine surgeons. Satisfactory decompression of the lateral recess and foramina is achieved under direct vision. Palpation of the pedicle and foramina, with a blunt ball-tipped nerve hook, ensures correct orientation and complete decompression. If decompression is required at another level, the incision can be elongated and a separate dilation performed. The wound is copiously irrigated, and hemostasis is achieved using electrocautery as the working channel is slowly removed under direct vision. The wound is closed in layers with absorbable sutures and Steri-Strips or Dermabond can be used on the skin.

2.8 Surgical Technique in Open Surgery

For the open technique, a patient is placed under general anesthesia and positioned prone on a Jackson or Andrews frame, with all bony prominences well padded. It is important to ensure that the patient’s abdomen hangs freely; this decreases intra-abdominal pressure, which in turn will help reduce the distension and bleeding from epidural veins. Alternately, the patient may be placed on a Wilson frame, which allows the spine to be flexed, opening the interspace and providing easier access to the epidural space. The authors, however, prefer a Jackson frame because it places the spine in a more anatomic position with lumbar lordosis, positioning the spine in the position of greatest symptomatic stenosis. Fluoroscopy or surface anatomic landmarks may be used to localize the incision. A mid-line incision is centered over the affected level(s). Dissection is carried down through the skin and subcutaneous tissue to the fascia. The fascia is incised in the midline and the underlying spinous processes and laminae are exposed in a subperiosteal fashion. Care must be taken to preserve the facet capsules. In addition, the pars interarticularis should be identified at each level. Deep self-retaining retractors are then placed, and exposure of the intended levels is confirmed radiographically.

The interspinous ligament is removed at the intended level(s) of decompression. Using a rongeur or bone cutter, the spinous processes are removed. A high-speed burr can be used to create a small trough medial to the facet joints on each side. The lamina is then thinned with the burr, and the laminectomy completed using a Kerrison rongeur. Alternately, an ultrasonic bone scalpel may be used to cut through the lamina on each side, after which the lamina can be elevated and removed en bloc. Once the midline laminectomy is performed, the remaining ligamentum flavum is also removed. The lateral recesses bilaterally are then decompressed by undercutting the lamina with a Kerrison rongeur. The decompression can be extended laterally to the medial third of the facet joint, and foraminotomies can be performed to decompress the exiting nerve roots through the neuroforamina. The midline laminectomy should extend just lateral to the lateral border of the thecal sac; however, care must be taken to leave at least 5 mm of pars interarticularis intact; thinning the pars too much from medial to lateral (or from ventral to dorsal while decompressing the lateral recess) can predispose to fracture. Palpation within the epidural space, following the nerve roots into the neuroforamina, confirms that the decompression is complete.

The wound is then copiously irrigated with saline solution and hemostasis is achieved. A Valsalva maneuver is performed to ensure there is no leakage of cerebrospinal fluid (CSF). The deep retractors are released, the muscle is allowed to fall back into the midline, and the wound is closed in layers.

2.9 Discussion for Minimally Invasive Surgery

Minimally invasive lumbar decompression is commonly performed for the treatment of degenerative spinal stenosis as a result of intervertebral disc bulge, ligamentum flavum hypertrophy and calcification, and facet joint hypertrophy. This technique provides excellent access for decompressing the neural elements and offers advantages over traditional open laminectomies. Furthermore, the MIS technique minimizes approach-related morbidity and disruption of normal anatomy incurred with OS. In this chapter’s illustrative case, a minimally invasive approach for lumbar decompression via tubular retractors should allow for adequate direct decompression of the entire spinal canal using a unilateral approach. A critical review of published results should provide insight into the advantages of a minimally invasive approach compared to traditional open laminectomy ( Table 2.1).

2.9.1 Level I Evidence in Minimally Invasive Surgery

There are no level I studies available.

2.9.2 Level II Evidence in Minimally Invasive Surgery

Two prospective, randomized trials comparing MIS to open laminectomy have been published in the literature, albeit in small cohorts. Mobbs et al compared MIS to open laminectomy with respect to postoperative recovery and clinical outcomes by enrolling a total of 79 patients (data for analysis were available for only 54 patients) with symptomatic, radiographically confirmed lumbar spinal stenosis at a maximum of two levels between 2007 and 2009.29 The patients were randomly assigned to either open decompressive laminectomy or MIS according to their sequence of presentation. The authors demonstrated statistically significant improvements in clinical outcome, that is, ODI and VAS scores for both open and minimally invasive interventions. However, patients treated with the MIS technique had a significantly better mean improvement in the VAS score but not the ODI scores compared with patients in the open laminectomy group. In addition, Mobbs et al noted shorter length of postoperative hospital stay (55.1 vs. 100.8 hours) and time to mobilization (15.6 vs. 33.3 hours) and reduced opioid use for postoperative pain (15.4 vs. 51.9%) in patients undergoing MIS compared to open laminectomy. This study provides level II evidence that MIS achieves similar functional outcomes when compared with open laminectomy (ODI score), with the additional benefits of a greater decrease in pain (VAS score), postoperative recovery time, time to mobilization, and opioid use.

Yagi et al performed a prospective, randomized trial comparing the traditional open laminectomy approach to MIS using endoscopy for bilateral decompression of lumbar stenosis in 41 patients.³⁰ The authors reported no significant clinical differences (JOA [Japanese Orthopaedic Association] scale) between the two groups but noted a statistically significant lower VAS score for back pain at 1-year follow-up, and less blood loss (37 vs. 71 mL) and damage to the paravertebral muscles as measured by creatine phosphokinase muscular type isoenzyme (CPK-MM). This study provides level II evidence that MIS is comparable to clinical outcomes achieved with open laminectomy, while reducing postoperative back pain, blood loss, and length of stay.