The first description of a disc herniation causing sciatica was as early as 1934. For most patients, the radiculopathy associated with a herniated disc resolves nonoperatively, but for those in whom conservative management fails, surgical options can be considered. Treatment for such disc herniations has understandably evolved considerably as techniques continue to evolve. Chymopapain chemonucleolysis and automated percutaneous discectomy were two such techniques that have since fallen out of favor - chymopapain, for example, due to its risk of transverse myelitis. In the 1970s, the focus of surgical treatment shifted to a less invasive approach with decreased manipulation and trauma to the paraspinal musculature, ligamentum flavum, and affected nerve root.
The first documented experiences with the microdiscectomy technique using an operating microscope were in 1977 independently by both Yasargil and Caspar in Europe. In 1978, Williams was the first to popularize and publish the technique in the United States. Since then, studies have demonstrated the safety and efficacy of microdiscectomy compared to open discectomy and have published outcomes of decreased morbidity, quicker recovery, shorter hospital length of stay, and no significant difference with regard to long-term reoperation rates.
Today, 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.
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.
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.
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. 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 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.
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
Standard operating room staff personnel along with one or two surgeons and the anesthesiologist.
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.
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.
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. One large series of 2500 cases of microdiscectomy reported a complication rate of less than 1.5%. 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. 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. 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. 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. Microscope use was associated with increased operative time but no significant increased risk of infection.
Microdiscectomy is a safe and effective treatment for disc herniations. The landmark study of the Spine Patient Outcomes Research Trial used a large, multicenter, prospective, randomized controlled trial to compare open discectomy with nonoperative management. It has demonstrated that while both treatment groups did achieve good clinical outcomes, patients who underwent discectomy had greater improvement than those who had nonoperative management. A recent Cochrane database systematic review focused on open versus minimally invasive discectomy techniques. It presented low-quality data suggestive of lower infection rates, shorter hospital stays, but possibly inferior improvements in back and leg pain with the minimally invasive techniques. However, the authors acknowledged that these differences were small and potentially not clinically significant. A more recent systematic review and multiple prospective randomized trials comparing the common techniques for microdiscectomy, both open and tubular, have demonstrated Level 1 evidence to support that both techniques have similarly good outcomes and complication rates.
Achieving the best outcomes with a microdiscectomy relies on an interdisciplinary approach. Establishing the correct diagnosis is critical and begins in the primary care setting. Physicians must recognize the signs and symptoms of a painful herniated disc so that they may begin the appropriate workup. Imaging technicians and radiologists are also integral to the diagnostic process - especially with the role of advanced imaging modalities like MRIs. Conservative treatment relies on a combination of physicians and pharmacists to help manage the patient’s pain and prescribe appropriate multimodal medications in an attempt to minimize narcotic utilization. These can include a combination of anti-inflammatory medications, muscle relaxants, antidepressants, or gabapentinoids. It also relies on physical therapists to provide the gold-standard first line of conservative therapy, which can allow for successful treatment of most herniated discs without surgery. [Level 1] However, when conservative management fails to alleviate a patient’s symptoms or if the symptoms worsen, prompt recognition by the healthcare providers is essential.
A coordinated interdisciplinary approach across the healthcare professions is integral to a successful microdiscectomy. From the proper patient selection, diagnostic workup, and referrals to the exhaustion of conservative management, primary care practitioners, specialty-trained nurses, physicians such as those who provide epidural steroid injections, and physical therapists are as critical to the team as the surgeon.
While most of these procedures are done as an outpatient, it is important that patients are encouraged to mobilize postoperatively, ambulate as tolerated, and participate in physical therapy. It is also encouraged that the patients avoid excessive strain or lifting for the first six to eight weeks after surgery.
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