Introduction
Minimally invasive lumbar decompression (MILD) is an image-guided approach used in the treatment of symptomatic lumbar central spinal stenosis. This procedure is a good option for patients who are not responsive to conservative or injection therapy and either do not want an open surgical decompression or are not good surgical candidates. Lumbar spinal stenosis (LSS) is a degenerative disease of the aging spine. LSS is the most common indication for spinal surgery in patients above the age of 65.
Indication
The MILD procedure is indicated for patients with symptomatic central LSS due to ligamentum flavum hypertrophy. It is not meant for patients with symptoms due to lateral recess spinal stenosis. It is also not indicated if stenosis is due to any cause other than ligamentum flavum hypertrophy (e.g., anterolisthesis or disc protrusion). Indications and contraindications are summarized in Table 6.1 .
Indications | Contraindications |
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Patient selection
Patient selection is the most important part of the MILD procedure ( Table 6.2 ). The patient should have symptomatic central LSS from ligamentum flavum hypertrophy ( Fig. 6.1 ).
Primary indication | Neurogenic claudication in the presence of radiologically proven ligamentum flavum hypertrophy |
Neurogenic claudication symptoms |
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Symptom characteristics |
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Physical examination | Unremarkable; the presence of sensory or motor deficits should prompt surgical evaluation |
Imaging |
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Radiological criteria for spinal stenosis | There are several criteria used, but anterioposterior spinal canal diameter of <10 mm or an area of <70 mm 2 is generally considered diagnostic |
Diagnostic criteria used in various MILD trials |
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Setup
Table 6.3 describes some important aspects of the procedure setup.
Anesthesia |
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Positioning |
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Antimicrobial actions |
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Procedure
- 1.
Obtain an anterioposterior fluoroscopic view of the lumbar spine with the spinous process midway between the pedicles.
- 2.
Three straight lines are drawn:
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One in the middle (over the spinous processes)
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Two connecting the medial side of the pedicles on each side ( Fig. 6.2 )
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- 3.
Ideally, the insertion point is usually one and one-half to two vertebral levels below the target space, in the paramedian plane between the two lines initially drawn on the patient in the previous step.
- 4.
Provide cutaneous analgesia with a 25-gauge needle, then further anesthetize the cannula tract with a 22-gauge 3.5 inch spinal needle to the lower lamina, including the laminar periosteum.
- 5.
Obtain epidural space access. The epidural needle should be placed in the most cephalad part of the interlaminar space with the intent to obtain ipsilateral dye spread.
- 6.
After a skin stab, a 6-gauge working cannula via use of the trocar is inserted to the lower lamina.
- 7.
Lateral fluoroscopic guidance is used to ensure that it is not placed too deep (which will result in a large dural tear) ( Figs. 6.3 , 6.4 ).