43 Microdiscectomy

Microdiscectomy allows the surgeon to perform all of the maneuvers of the routine hemilaminotomy and discectomy procedure with the aid of improved illumination and magnification. Table 43–1 is a list of favored instruments. Familiarity with draping, positioning, and adjusting the operating microscope is necessary before the surgeon attempts to perform the procedure. The use of operating loupes and a head lamp is a viable alternative to the operating microscope; however, the operating microscope has distinct advantages.

Indications for Surgery

1. Radicular signs and symptoms of nerve root compression due to a disc herniation.

2. Unresponsive or inadequately responsive to symptomatic nonoperative treatment.

3. The offending disc herniation with nerve root compression must be demonstrated on a magnetic resonance imaging (MRI) scan, a computed tomography (CT) scan, or a myelogram.

Contraindications

1. Inconclusive diagnosis of herniated nucleus pulposus (HNP)

2. Symptom amplification

Advantages

1. Allows the surgeon to perform the procedure with greater accuracy and with less risk of complications due to the surgical misadventures of excessive bleeding, nerve root damage, dural lacerations, and missed and retained disc fragments.

2. The postoperative course is so predictable and benign that the surgeon can confidentially release the patient from the hospital the day of surgery, making this truly an outpatient surgical procedure.

3. Relatively few instruments are required for the procedure.

Procedure

The description of the technique that follows is a step-by-step guide that applies to the routine disc herniation (Fig. 43–1). The following special situations require deviations from the standard technique and are described separately:

1. Foraminal herniation

2. Far lateral herniation

3. Completely extruded fragment

4. Recurrent herniation

The surgery is usually performed with the patient in a prone position under general anesthesia. It is possible to use spinal, epidural, or local anesthesia; however, the benefits are not worth the added complexity and the occasional unpredictability of these regional anesthetic techniques. The patient is placed prone on any operating frame that allows abdominal decompression and flexion of the lumbar spine. The Wilson frame is the simplest, most readily available frame that meets these two criteria. The surgeon usually operates from the side of the disc herniation with the microscope positioned at the head of the table on the opposite side.

When the patient is anesthetized and positioned prone on the Wilson frame, in maximum flexion, the back is prepped and draped in routine fashion. A spinal needle is placed into the back at a location presumed to be the level of the disc herniation, and a lateral x-ray is taken to identify the exact surface location for the incision over the disc herniation. The opportunity to misinterpret the localizing x-ray, especially with nonstandard anatomy or obesity, must not be underestimated. Surgically exposing the wrong level is one of the most common surgical misadventures. When necessary, repeat x-rays must be taken, not only initially but also during the procedure to document absolutely the appropriate location of the surgical exposure. The skin incision size depends on the obesity of the patient; the more obese the patient, the larger the incision must be to allow access in the depths of the wound. Generally speaking, the incision is 1 to 2 inches in length. The size of the skin incision, however, is the least relevant aspect of the surgical procedure. It has never been reported that favorable results of discectomy surgery correlate with the length of the skin incision. The skin incision is in the midline; however, the fascial incision is made just lateral to the spinous processes, preserving the supraspinous and interspinous ligaments. Maintaining the interspinous and supraspinous ligaments is important to provide countertraction for the microdiscectomy retractor. With a Cobb elevator and digital dissection, the appropriate interlaminar space is exposed, palpated, and the facet identified. The microdiscectomy retractor is inserted. There are several retractors on the market that are adequate. The McCullough retractor with its blades of variable width and length is an excellent retractor system for this surgical procedure.

After insertion of the microdiscectomy retractor, the previously sterilely draped operating scope is brought into the field for the remainder of the procedure. The operating scope optimal for the microdiscectomy procedure must have a stand that is high enough to provide enough elevation to clear the patient’s back on the Wilson frame and focus in the depths of the wound with at least a 300-mm focal length objective lens. The focal length of the objective lens determines the space between the microscope and the surface of the back. Objective lenses of less than 300 mm do not provide enough space between the microscope and the back to perform surgery. Lenses over 350 mm are so far away from the back that the surgery can be awkward. The optimal focal length objective lenses depending on the size of the patient is 300 to 350 mm. The microscope head must also be adjustable in all planes with a universal joint. The surgeon must be able to angle the microscope head when necessary in every direction to obtain appropriate visualization. The initial view through the microscope of the operative field is frequently a confusing array of fat, muscle strands, and bleeding. Muscle and fat debris must be removed with a pituitary rongeur and bleeding controlled with electrocautery. Meticulous hemostasis is mandatory when performing this procedure. The facet joint is the most readily identifiable local anatomic landmark and is the key to surgical exposure. The inferior medial margin of the facet joint must always be identified. This is most expeditiously done by removing the falciform flavum and the inferior medial facet capsule with a 3-mm, 40-degree Kerrison rongeur. Except at the LS-S1 level, it is always necessary to perform a partial medial facetectomy of both the inferior and the superior facet. The use of a high-speed drill bur is frequently recommended for this bone removal; however, it is not necessary and invites excessive and unnecessary bone removal. The 3-mm, 40-degree Kerrison rongeur is the only instrument necessary for bone and ligamentum flavum removal.

Related posts:

Posterior Cervical Laminectomy and Fusion Odontoid Fixation Posterior Scoliosis Correction: King Type V/ Double Thoracic Curves Anterior Correction of Thoracic Scoliosis Using the Kaneda Anterior Scoliosis System (KASS) Anterior Lumbar Interbody Fusion Total Lumbar Disc Replacement Using the SB III Charite Prosthesis

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