Microdiscectomy – Indications, Contraindications

Microdiscectomy also sometimes called microdecompression or microdiscectomy, is a minimally invasive surgical procedure performed on patients with a herniated lumbar disc. During this surgery, a surgeon will remove portions of the herniated disc to relieve pressure on the spinal nerve column.

Microdiscectomy with its smaller incision, less traumatic approach, and better visualization of the operative field compared to standard open discectomy is considered the gold standard for removal of most lumbar disc herniations. Because of its collinear light and magnification, an operating microscope is preferred; however, magnifying loupes and a headlight may also be used. Most procedures are now done in the outpatient setting.

Anatomy and Physiology

Understanding anatomical landmarks is critical. Palpation of bony landmarks, including spinous processes, the sacrum, and iliac crests (usually corresponding to the L4/5 disc level), may guide the start point and trajectory of the surgical approach. Such landmarks may be difficult to palpate as body mass index increases – for these patients, it is especially important to ensure the accuracy of trajectory throughout the approach. Disorientation during the procedure can also occur, especially under the operating microscope.

Lumbosacral Transitional Vertebrae

Beware of transitional anatomy. Low back pain in the presence of a lumbosacral transitional vertebra is referred to as Bertolotti syndrome. L5 may sometimes be “sacralized” (with L5 fused to the sacrum), or S1 may be “lumbarized” (with a well-developed disc seen between S1 and S2). It is, therefore, essential to study preoperative imaging and to confirm agreement of the level intraoperatively as the incidence of transitional vertebrae can be as high as 4.6% of the general population.[rx]

Nerve Roots

It is important to understand the difference between a traversing and exiting nerve root to better characterize the pathoanatomy of a disc herniation. The location of a disc herniation can determine the surgical approach. Nerve roots exit the spinal canal at the level of the corresponding pedicle (with the exception of those in the cervical spine). For example, the L4 nerve root crosses the L3/4 disc space centrally, or traverses, and exits the spinal canal beneath the L4 pedicle. It then crosses the L4/5 disc space at its lateral margin. This concept is critical to delineate from where a patient’s symptoms may be arising. A paracentral disc herniation at L4/5 would result in compression of the L5 traversing nerve root, whereas a foraminal disc herniation at the same level would compress the exiting L4 nerve root, possibly both the L4 and L5 nerve roots. A far-lateral disc herniation lies beyond the lateral intervertebral space outside the facet joint.

Indications of Microdiscectomy

General indication for microdiscectomy is a patient with single-level disc herniation and evidence of nerve root compression that has residual or unremitting radicular symptoms after failed conservative treatment modalities. The predominance of radicular rather than lumbar pain is an important consideration as the former is the most likely to improve post-operatively. Urgent surgical indications include disc herniations resulting in cauda equina syndrome as well as progressive or new motor deficits.

Neuroimaging studies suggestive of disc herniation with corresponding clinical symptoms is essential.[rx][rx] MRI is the preferred diagnostic modality; however, when contraindicated, CT myelogram may be performed. A plain CT may be acceptable when intrathecal contrast is contraindicated.

Contraindications of Microdiscectomy

Contraindications include concomitant pathology such as infection or tumor, as well as segmental instability or vertebral fractures in which further fusion or instrumentation would be required. However, some physicians consider spondylolisthesis or segmental instability only a relative contraindication in certain patients, as long as there is appropriate counseling regarding the potential need for further operative fixation if the microdiscectomy does not succeed. Microdiscectomy is also not recommended for disc fragments medially causing cord compression. This is relevant in the cervical and thoracic spine.

Equipment

• Standard radiolucent table with Wilson frame (versus Jackson spine flat top table)
• Fluoroscopy/C-arm to localize level and minimize skin incision
• Operative microscope (in from the opposite side of C-arm), or headlight and magnifying loupes
• Microdiscectomy set including high-speed drill, Kerrison rongeurs
• Bipolar cautery

Personnel

Standard operating room staff personnel along with one or two surgeons and the anesthesiologist.

Preparation

After administration of general anesthesia, the patient is positioned prone on a spine frame or designated table. Local anesthesia may be used; however, general is preferred to manage both the airway and hemodynamics better. The head is positioned on a foam support with orbital and facial cutouts to minimize pressure on the eyes, nose, and mouth, while also allowing for airway access. The arms are positioned with shoulders at 90 degrees abduction and elbows at 90 degrees flexion with the axillae free of compression to prevent neuropraxia of the brachial plexus. Ensure chest support with padding, so nipples are midline and straight down. The anterior superior iliac spine and knees are positioned on gel pads with slight flexion of the hips and knees. Check to make sure there is no compression on the lateral femoral cutaneous nerve, peroneal and ulnar nerves. Placing the lumbar spine in kyphosis facilitates access by opening the interlaminar space. Ensure the abdomen is free to reduce intra-abdominal pressure, thereby reducing central venous pressure and epidural venous congestion to minimize surgical site bleeding.

Administer prophylactic intravenous antibiotics before skin incision. Fluoroscopic imaging is used for localization and to make the most accurate skin incision directed over the appropriate interspace. A spinal needle can be utilized to mark the incision site with image guidance. The skin is prepped in the usual sterile fashion.

Technique

Open Midline Microdiscectomy

Using intraoperative radiography to confirm the target level, a two to three centimeter marking for a longitudinal midline incision is made over the interspace. Skin incision is made with a sharp scalpel, and subcutaneous dissection with electrocautery reveals the lumbar fascia over the midline. The muscular aponeurosis is incised just off of midline on the side of the approach, and the multifidus is released subperiosteally from the spinous process on one side out to the facet joints with a Cobb elevator. The dissection should include half of the lamina both above and below the interspace. Do not violate the facet capsule. At this point, repeat imaging should be performed to confirm the appropriate level. Retractors are introduced to establish the working window, and the microscope is positioned accordingly over the incision. Magnifying loupes can be used alternatively.

The ligamentum flavum is exposed and released with a curette from its attachment on the anterior aspect of the superior lamina of the inferior vertebra. The ligamentum flavum is then incised sharply to allow for its retraction. An angled Woodson elevator can be used beneath the ligamentum to protect the dura during this incision Retraction of the ligamentum, or removal with a Kerrison rongeur should allow for visualization of the exiting nerve root with its associated epidural fat. The nerve root must be identified before proceeding to disc resection. If visualization is inadequate, the medial aspect of the inferior facet of the superior vertebra may need to be removed. To minimize the risk of iatrogenic instability, it is important to preserve at least half of the facet joint, and 8 to 12 mm of bone from the lateral edge of decompression to the edge of the pars interarticularis. A laminotomy of the inferior portion of the upper lamina may be necessary if the disc is not centered on the interlaminar space. A blunt ball-tipped probe is inserted into the neuroforamen to mobilize the nerve root, which is then retracted medially with a nerve root retractor. Disc excision can now be performed with removal of the fragmented or herniated disc tissue.

In some cases, the annulus must be incised to remove a portion of disc from behind the posterior longitudinal ligament. Up- and down-facing curettes and pituitary rongeurs can be used to perform the discectomy. Care is taken not to violate anteriorly beyond the disc space where major vessels lie – especially important when using the microscope. Using a blunt instrument such as a Penfield dissector or a Woodson elevator, freedom of the nerve and dural sac is checked by probing in all directions to check for any remaining disc or ligamentous tissue, and to confirm an adequate decompression.

Irrigate the disc space with saline via a hollow flexible tube or bulb syringe to express any unrecognized loose disc fragments. Meticulous hemostasis is obtained with bipolar cautery, and the wound is thoroughly irrigated with saline. Vancomycin powder can be applied to the wound prior to closure. The fascia of the lumbar musculature and subcutaneous layers are closed with absorbable suture, and the skin is closed according to surgeon preference. Some disc herniations, such as those extending through the foramen, may need to be approached from a combined midline and lateral approach.

Open Transmuscular Far-lateral Microdiscectomy

The same general steps can be applied but approached through the muscle-splitting technique to avoid the extensive muscle retraction that would be necessary from a midline approach. In this case, incision is made 3.0 to 6.0 cm off midline on the side of the affected level. Skin incision is made with a sharp scalpel, and subcutaneous dissection with electrocautery reveals the thoracolumbar fascia. Muscle fibers of the superficial lumbar musculature are split longitudinally. Specifically, the fibers of the multifidus and longissimus muscles are bluntly separated. Self-retaining retractors can now be introduced, and the microscope is positioned over the working window (similarly, the surgeon can proceed instead with the assistance of magnifying loupes). Surgical landmarks are identified, including the pars interarticularis or isthmus, transverse processes, facet joint, and intertransverse ligament. The intertransverse ligament can be detached from the inferior transverse process and retracted laterally. If needed, a Kerrison rongeur or high-speed drill can be used to remove a portion of bone along the superior aspect of the isthmus as well as the inferior portion of the superior transverse process. At this point, the ligamentum flavum is visualized as well as the inferior aspect of the pedicle beneath the transverse process. Resect the ligamentum flavum using a Kerrison rongeur for better visualization of the nerve and to avoid injury. The nerve is typically displaced superiorly and laterally by the underlying disc material. Dissect lumbar arteries and veins from the lower foramen when possible and inspect for any further migration of the herniated disc. Carefully examine the foramen for any disc fragments with a blunt nerve hook as the nerve exits inferior to the pedicle. Irrigate and close the wound as detailed above.

Minimally Invasive Tubular Microdiscectomy

The patient is positioned and prepped as described above. A 1.5 to 2.0 cm surgical incision is marked longitudinally 1.5 cm paramedian to the midline on the affected side for paracentral herniations. For extraforaminal or far-lateral disc herniations, the incision is marked 3.0 to 5.0 cm paramedian to the midline. An incision is made with a scalpel to facilitate the blunt muscle-sparing dissection through serial placement of dilators. The dilators are placed under direct vision with fluoroscopy to ensure appropriate depth and localization, as well as to create a working channel. At this point, the microscope can be introduced to the surgical field, or magnifying loupes can be used to aid in visualization. Once the bony exposure of the spine is visible within the tubular retractor, hemilaminotomy and discectomy can be performed as needed in a similar manner as in the open exposures detailed above. Once hemostasis is achieved, the tubular retractor system can be removed, and subcutaneous tissue and skin can be closed.

What happens after surgery?

You will awaken in the postoperative recovery area, called the PACU. Blood pressure, heart rate, and respiration will be monitored. Any pain will be addressed. Once awake, you will be moved to a regular room where you’ll increase your activity level (sitting in a chair, walking). Most patients can go home the same day. Other patients can be released from the hospital in 1 to 2 days.

Discharge instructions

Discomfort

• Take pain medication as directed by your surgeon. Narcotics can be addictive and are used for a limited period of time.
• Narcotics can also cause constipation. Drink lots of water and eat high-fiber foods. Laxatives and stool softeners such as Dulcolax, Senokot, Colace, and Milk of Magnesia are available without a prescription.
• Ice your incision 3-4 times per day for 15-20 minutes to reduce pain and swelling.

Restrictions

• Avoid bending, lifting or twisting your back for the next 2 weeks.
• Do not lift anything heavier than 5 pounds for 2 weeks after surgery.
• No strenuous activity for the next 2 weeks including yard work, housework and sex.
• Do not drive for 2 weeks after surgery or until discussed with your surgeon.
• Do not drink alcohol for 2 weeks after surgery or while you are taking narcotic medication.
• Do not smoke. Smoking delays healing and inhibits bone growth.

Activity

• You may need help with daily activities (e.g., dressing, bathing) for the first few days. Fatigue is common. Let pain be your guide.
• Get up and walk 5-10 minutes every 3-4 hours. Gradually increase your walking time, as you are able.

Bathing/Incision Care

• Wash your hands thoroughly before and after cleaning your incision to prevent infection.
• If you have Dermabond (skin glue) covering your incision, you may shower the day after surgery. Gently wash the area daily with soap and water. Pat dry.
• If you have staples, steri-strips or stitches, you may shower 2 days after surgery. Remove the gauze dressing and gently wash the area with soap and water. Replace the dressing or completely remove it if no drainage. Inspect and wash the incision daily.
• Do not submerge or soak the incision in water
  (bath, pool or tub).
• Do not apply any lotions or ointments over the incision.
• Some drainage from the incision is normal. A large amount of drainage, foul smelling drainage, or drainage that is yellow or green should be reported to your surgeon’s office.
• Staples, steri-strips, and stitches will be removed at your follow-up appointment.

When to Call Your Doctor

• If your temperature exceeds 101.5° F, or if the incision begins to separate or show signs of infection, such as redness, swelling, pain, or drainage.
• Swelling and tenderness in the calf of one leg.
• New onset of tingling or numbness in the legs or numbness in the groin area.

Complications

Complications of microdiscectomy range from iatrogenic injuries such as durotomy, nerve root injury or instability, to recurrent disc herniations, hematoma, infections, or even other medical complications. Reported complication rates vary. Incidence of durotomy ranges from 0.7% to 4% in the literature but is undoubtedly higher in cases of revision microdiscectomy.[rx][rx][rx][rx] One large series of 2500 cases of microdiscectomy reported a complication rate of less than 1.5%.[rx] A recent systematic review and meta-analysis analyzed the complication rates following several different microdiscectomy approaches. Overall, the published complication rates for open and percutaneous microdiscectomy was 12.5% and 10.8%, respectively. This included intraoperative nerve root injury (2.6% and 1.1%), new or worsening neurologic injury (2.6% and 1.1%), hematoma (0.5% and 0.6%), wound complications including infection, dehiscence, or seroma (2.1% and 0.5%), recurrent disc herniations (4.4% and 3.9%), and reoperation (7.1% and 10.2%). Interestingly, these numbers show the general incidence of different complications, yet no differences were statistically significant between the types of microdiscectomy.[rx] Studies show conflicting evidence for risk factors of recurrent lumbar disc herniations with regards to sex, age, and body mass index; however, smoking, heavy labor, taller disc height, and presence of degenerative facet changes seem to be associated with recurrent herniation.[rx][rx] Other than the risk of recurrent herniation, other issues of back pain postoperatively can be due to further disc degeneration or facet arthritis leading to segmental instability. These other etiologies can be difficult to quantify and are therefore not frequently reported or published.

Despite the benefits a microscope can add, many surgeons have been reluctant to adopt its use secondary to concerns regarding a potential increased risk of infection. Studies have confirmed that microscopes, as well as surgical loupes and headlamps, can all be reservoirs of microorganisms.[rx][rx] One study, in particular, examined cultures of samples taken intraoperatively from the cover of the microscope and the disc space. While 17% of patients had a positive sample from the disc space, and 12% had a positive sample from the microscope, there was only one case of clinically significant infection of their more than 400 patients studied.[rx] Microscope use was associated with increased operative time but no significant increased risk of infection.[rx]