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Spinal stenosis refers narrowing of the spinal canal, which causes compression of neural structures in the spinal column. When it occurs in the low back, the condition is called lumbar spinal stenosis.
Lumbar spinal stenosis generally results from degenerative changes in the lumbar spine, such as thickening of ligaments, arthritic changes in spinal joints, and bulging of intervertebral disks. Compression of the lumbar neural elements (e.g., spinal cord, nerve roots) manifests as neurogenic claudication, or low back and leg pain especially on standing and walking (Tumialán, 2012).
Mild®, or minimally invasive lumbar decompression, is a technique approved by the Food and Drug Administration (FDA) in 2006 to treat lumbar stenosis. Mild® uses fluoroscopy, or real-time x-ray guidance, epidural contrast, and a specially designed tool kit to remodel obstructive tissues contributing to the stenosis.
True to its name, Mild® is a relatively gentle procedure. The procedure is performed with only local anesthesia and light sedation, and small incisions relatively close to the surface of the skin. This makes Mild® minimally invasive and reasonably safe when performed by a skilled practitioner.
The vertebral column, or spine, in most individuals consists of 33 vertebrae that run in a line from the base of the head to the buttocks. Each vertebra consists of a vertebral body and an arch. The ligamentum flava (singular: flavum), two ligaments often implicated in spinal stenosis, run the length of the spinal column, connecting adjacent laminae (broad bone plates) that fuse to form each vertebral arch.
The vertebral arches serve attachment points for muscles and ligaments and form joints that serve as sites of articulation with adjacent vertebrae. The arches also align to form a canal, which houses the spinal cord and its protective membranes (meninges), blood vessels, and other tissues. A total of 31 pairs of spinal nerves emerge from the vertebral canal between adjacent vertebrae. The sciatic nerves, which begin in the low back, are particularly prone to irritation from lumbar stenosis, which manifests as pain, burning, or tingling that radiates down the buttocks and legs.
Also located between vertebrae are intervertebral disks, which act as cushions. As the disks age, they lose water content, becoming dry and brittle. This loss in suppleness can lead to bulging or herniation of the disks, which can in some cases contribute to spinal stenosis.
In lumbar spinal stenosis, thickening, displacement and deterioration of tissues in the low back due to degenerative disk disease, arthritis, and other causes can compress the delicate spinal cord and nerve roots, resulting in irritation, inflammation, and pain. Unfortunately, if left untreated these neurological symptoms are progressive.
The Mild® procedure involves percutaneous laminotomy, or removal of laminae that fuse to form the vertebral arch, and thinning of the ligamentum flavum in order to increase the critical diameter of the narrowed spinal canal and affected nerve roots (Deer & Kapural, 2010).
The patient is given light sedation and local anesthesia. Next, the epidural space is filled with contrast medium. Under fluoroscopic guidance, single-use tools are passed through a hollow needle, or cannula, to resect obstructive tissues (e.g., thickened ligamentum flavum, small pieces of lamina) (Deer & Kapural, 2010) thereby releasing pressure on the spine and associated nerves. This tissue and bone sculpting is repeated on the opposite side of the spine for complete decompression of the central canal.
A significant benefit of Mild® is its minimally invasive nature. Less invasive interventions are associated with fewer risks and post-procedural complications. Relatively quick to perform and done without large incisions, Mild® can help patients avoid open surgery (e.g., spinal fusion), which is more invasive and risky.
According to three unrelated, recent, high-quality studies, Mild® was shown to be a safe, effective, and cost-effective treatment for lumbar spinal stenosis in patients with neurogenic claudication (Basu, 2012; Chopko & Caraway, 2010; Mekhail et al, 2012). In all three studies, patients experienced significant reductions in pain, as measured by various pain scales, improvements in mobility and quality of life, and no significant mild device or procedure-related adverse events. One researcher commented, “The safety profile of mild, combined with the significant improvement in quality of life for these patients at 6-months is remarkable.”
The encouraging safety profile of Mild® as reported in the medical literature suggests the procedure is low risk and has a relatively low incidence of complications. For example, a survey conducted on 90 consecutive patients who underwent the Mild® procedure found no major adverse events or complications related to the devices or procedure. Specifically, no incidents of dural puncture or tear, blood transfusion, nerve injury, epidural bleeding, or hematoma were observed (Deer & Kapural, 2010). The researchers concluded the study demonstrates the acute safety of the mild procedure with no report of significant or unusual patient complications.
Also, a one-year follow-up study on 58 Mild® patients who underwent 170 procedures (the majority treated bilaterally at one or two lumbar levels) found no major Mild® device or procedure-related complications (Mekhail et al, 2012). After one year, the patients showed a significant reduction in pain as measured by visual analog scale (VAS). Improvement in physical functionality, mobility, and disability was significant as measured by Oswestry Disability Index (ODI), Zurich Claudication Questionnaire (ZCQ), and SF-12v2® Health Survey. The researchers concluded at one year the 58-patient cohort demonstrated continued excellent safety profile of the mild® procedure and showed long-term pain relief and improved functionality.
It is crucial to seek prompt treatment for lumbar spinal stenosis, since the pain, disability and neurological compromise caused by the condition may worsen over time. Also, as patients with more advanced cases of the condition may not be appropriate candidates for Mild® (Ewald & Kalff, 2011), early treatment is important.
- Basu S. (2012). Mild procedure: single-site prospective IRB study. Clin J Pain. 28(3):254-8.
- BlueCross BlueShield of North Carolina. (2010). Image-Guided Minimally Invasive Lumbar Decompression (IGMLD) for Spinal Stenosis. Retrieved March 30, 2010 from http://www.bcbsnc.com/assets/services/public/pdfs/medicalpolicy/image-guided_minimally_invasive_lumbar_decompression_for_spinal_stenosis.pdf
- Chopko B, & Caraway DL. (2010). MiDAS I (mild Decompression Alternative to Open Surgery): a preliminary report of a prospective, multi-center clinical study. Pain Physician. 13(4):369-78.
- Deer TR, & Kapural L. (2010). New image-guided ultra-minimally invasive lumbar decompression method: the mild procedure. Pain Physician. 13(1):35-41.
- Ewald C, & Kalff R. (2011). [Symptomatic lumbar spinal stenosis: diagnostic evaluation and therapeutic strategies]. [Article in German]. Nervenarzt. 82(12):1623-29.
- Mekhail N, Vallejo R, Coleman MH, & Benyamin RM. (2012). Long-term results of percutaneous lumbar decompression mild(®) for spinal stenosis. Pain Pract. 12(3):184-93. doi: 10.1111/j.1533-2500.2011.00481.x.
- Tumialán LM, Marciano FF, & Theodore N. (2012). Regarding: long-term results of percutaneous lumbar decompression mild for spinal stenosis. Pain Pract. 12(3):252; author reply 252-3. doi: 10.1111/j.1533-2500.2011.00509.x.
- X-Sten MILD Tool Kit Section FDA 510(k) premarket notification approval. 2006. Retrieved March 30, 2010 from http://www.accessdata.fda.gov/cdrh_docs/pdf6/K062038.pdf