Lumbar Discectomy

Lumbar discectomy is the most common operation performed in the United States for lumbar-related symptoms.[1] Lumbar disc herniation accounts for only 5% of all low back pain problems but is the most common cause of radiating nerve root pain (sciatica).[2]

Mixter and Barr described the first surgical procedure to remove the herniated lumbar disc in 1934 through a laminectomy and durotomy, with later enhancement by Semmes, who described approaching the herniated disc through hemilaminectomy and retraction of the dural sac. This became popularized as the “classical discectomy technique.”[3]

During the latter half of the 19th century, more techniques were developed to remove the herniated disc with minimal invasiveness[4] . The first herniated disc excision using a microscope (microdiscectomy) was performed by Yasargil in 1977, which was the standard surgical procedure at the time. In 1993, Mayer and Brock and then in 1997, Smith and Foley described endoscopic discectomy techniques.[3] With these minimally invasive techniques, authors demonstrated decreased soft tissue manipulation, operative time, blood loss, and hospital stay, allowing early recovery.[5]

The natural history of lumbar disc herniation indicates that they may decrease in size or even disappear within a few weeks or months of onset. In migrated or extruded herniations, phagocytosis of the herniated disc by the macrophages occurs, while, in contained herniations, dehydration of the herniated nucleus pulposus plays a major role in the reduction of the herniated disc size.

The literature suggests that lumbar discectomy provides effective clinical benefit in carefully selected patients with sciatica. There is strong evidence in favor of microdiscectomy surgery over conservative treatment at short-term follow-up, but, at long-term follow-up, there is no significant difference among patients with subacute lumbar disc herniation with associated radiculopathy (LDHR) between the two groups.[6] Overall, the long-term benefits of surgery versus nonoperative treatment are still unclear.

Approximately 90% of acute sciatica attacks improve with conservative management; thus, the mainstay of treatment for a patient with symptomatic lumbar disc herniation continues to be nonoperative methods, such as treatment with anti-inflammatory medications, physical therapy, and lumbar injection, unless the patient has an acute or progressive neurological deficit.

Indications for lumbar discectomy include altered bladder and bowel function and progressive neurological deficits such as motor weakness or sensory deficit in the lower extremities. Surgery should also be considered in patients with radicular pain that persists after an adequate course of conservative management.

Lumbar discectomy has no absolute contraindications. However, below are some factors to consider before deciding on lumbar discectomy.

Clinical/radiological discrepancy: A patient with clinical findings that do not correlate with the radiological findings is unlikely to benefit from surgery. Typically, this occurs with symptoms on the opposite side or at a different level from the disc.

Primarily back pain: Patients with mostly back pain are not good surgical candidates. The patients who benefit most from surgery are those who primarily have radicular pain (sciatica).

Inadequate conservative treatment: Patient should be given a trial of adequate conservative management (at least 6 weeks of physical therapy) before surgical intervention, since 90% sciatica cases improve with conservative treatment alone.

The most common complications associated with lumbar discectomy performed in the prone position are nerve palsies and compression injuries due to inappropriate positioning, exaggerated limb stretch, and inadequate padding. Simple padding with cushions, sheets, blankets, or egg-crate padding prevent these complications. Brachial plexus injuries can result from excessive abduction of the shoulders.

Proper preoperative planning and intraoperative radiographic localization are important to prevent wrong-level surgery. It is important to compare the appearance of the lumbar and sacral vertebrae on preoperative studies with intraoperative localizing films to determine the proper level. Some patients have a transitional vertebral that could be considered either L5 or S1. As long as the nomenclature is consistent, wrong-level surgery can be avoided. Be careful that there is no movement of the localizing instrument between taking the radiograph and visual confirmation in the operative field.

See Background.

The complications from lumbar discectomy can be broadly divided into 2 major groups, intraoperative and postoperative, related to the time course when they occur.

Intraoperative complications

Wrong-level surgery: One comparative study reported that wrong-level surgery occurs in 3.3% of cases performed by less-experienced surgeons and 1.2% of cases performed by very experienced surgeons.[7] Proper preoperative planning and intraoperative vigilance is important to prevent wrong-level exploration.

Dural tear: Injuries to the dura with consequent CSF leak can generally be recognized intraoperatively. Weinstein et al reported in a review article that this occurs in 3% of cases.[8] If detected intraoperatively, it can be primarily repaired with 6-0 Prolene. After a good dural closure has been obtained, patients can be mobilized the same day, although some surgeons prefer to keep their patients on bedrest for 48 hours or longer after dural repair.

Nerve root injury: Iatrogenic nerve injuries occur more commonly in reoperations because of scarring but can also occur in primary operations, resulting from vigorous retraction, unidentified conjoined nerve roots, and large disc herniations. Nerve root injury after lumbar spine surgery has been reported to occur in about 0.2% cases.[9] The most vulnerable region for a nerve root injury is the axilla of the nerve root, so it is recommended to stay as lateral to the nerve root as possible. Identifying the nerve root and thecal sac before removing the disc fragments can also decrease the risk of injury.

Anterior vessel or visceral injuries: The vessels that lie anterior to the anterior longitudinal ligament can be inadvertently damaged with aggressive removal of disc from the anterior interspace. The most frequently reported injury is that of the left common iliac artery caused by maneuvers in the L4/5 disc space. Fortunately, anterior vessel injury is rare, with an overall reported complication rate of 0.045%. The mortality rate reported with this complication, even with prompt reaction, is around 50%.[10] In about half of cases, the anterior vessel injury can be diagnosed during surgery, with the rest of the cases identified later, usually upon resulting hypotension and painful abdominal swelling.

Postoperative complications

Infection: The disc space infection rate after lumbar discectomy ranges from 0.13%-0.9%.[11, 12] Infections after lumbar discectomy can be classified as superficial or deep wound. The superficial infection rate after lumbar discectomy is around 2%-3%, which is similar to other surgeries. Deep infections typically present as epidural abscess or discitis, which can involve the surrounding vertebral bodies, resulting in spondylodiscitis. Postoperative spondylodiscitis can be treated with systemic antibiotics; however, if the patient develops an abscess, it may need surgical or percutaneous drainage under CT guidance.

Recurrent disc herniation: The incidence of recurrent lumbar disc herniation resulting in reoperation ranges from 3%-18% in patients undergoing first-time disc surgery.[13] Often, patients have a pain-free interval before they present with recurrent pain in the original pain distribution. Lebow et al showed that 23.1% patients demonstrated radiographic evidence of recurrent disc herniation at the level of prior discectomy on serial imaging, occurring about a year after surgery. The recurrent disc herniation was asymptomatic in 13% of patients and symptomatic in 10.2%. The symptomatic patients underwent revision discectomy.[14]

Thromboembolic complications: Patients are at risk of thromboembolic complications during the perioperative period. The reported rate of embolic complications range from 0.1%-1%, and the rate of lower-extremity thrombosis is likely higher than this.[15] Sequential compression devices (SCDs) should be used during the surgery to decrease the risk of thromboembolism. If a patient requires prolonged bedrest following surgery, subcutaneous heparin or the equivalent should be used.

Nerve palsies related to positioning: Brachial plexus stretch due to hyperabduction of the arm and ulnar and radial nerve palsies can result from inappropriate positioning of the arm during surgery. The shoulder should not be abducted more than 45°, and bony prominences such as elbows and wrists should be properly padded.

Persistent symptoms[16] : Persistent symptoms typically result from inadequate removal of the herniated disc, wrong-level surgery, or nerve injury from retraction. Careful preoperative planning and accurate radiographic localization during surgery can minimize these complications.

Standard lumbar discectomy equipment includes self-retaining retractors, high-speed handheld drills, Kerrison and Leksell rongeurs, pituitary rongeurs, and various straight and angled curettes. Surgical loupes and an operating microscope help in visualization and improved illumination. Intraoperative use of the C arm is important for localization of the desired spinal level.

Anesthesia

In most cases, the discectomy is performed under general endotracheal anesthesia. Regional anesthetic techniques such as spinal epidural block can also be used for lumbar discectomy, but local anesthesia is not advised.

Positioning

The patient is anesthetized in the supine position and then turned into the prone position on the Jackson table or other suitable operating table with the Wilson frame, which helps open the interlaminar space and improves access to the disc. The endotracheal tube must be firmly secured and the eyes appropriately lubricated and eyelids closed and protected before turning the patient into the prone position.

The patient’s chin is inspected to ensure it is free from compression, and the breasts are medially displaced to prevent pressure on the nipples. The groin, anterior superior iliac spine and knees are appropriately padded with the abdomen resting as free as possible to prevent venous compression, which can lead to worsened intraoperative bleeding.

Lower-extremity pulses should be checked to ensure that the abdominal aorta and femoral arteries are not compressed. A padded roll is placed under the ankles so the knees are bent and feet suspended. The upper extremities should be positioned with the shoulder abducted to about 45° and elbow flexed to about 90°. The elbows should be supported with adequate foam padding to prevent nerve compression, mainly of the ulnar nerve, which lies subcutaneously at this level.

Patients can experience more pain in the immediate postoperative period than in their preoperative state, mainly owing to paraspinal muscle stripping. For this reason, patients are continued on their preoperative pain regimen. Some patients require supplemental pain medications to cover the postoperative period. Pain control usually involves a combination of narcotic analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs), and muscle relaxants. Inadequate postoperative pain control can be counterproductive, since it may limit the patient’s physical activity and involvement in physical therapy programs.

Patients are typically discharged home the next morning or sometimes the same day and are allowed to do activities as tolerated with only a few limitations. They are encouraged to ambulate as soon as the postoperative pain can be tolerated but must avoid heavy lifting (no more than 10-15 pounds) and strenuous physical activity for a variable period, which is determined by the surgeon.

Patients with sedentary work can resume their work in 1-2 weeks, while patients with more physically demanding jobs may have to wait longer before resuming work. At one-month follow-up, physical restrictions are lifted, and patients are encouraged to gradually increase their physical activity, as tolerated, to normal. Light aerobic activities and walking are encouraged to prevent general complications such as deep venous thrombosis and pneumonia and to reduce local muscle spasm.

Further treatment such as physical therapy or rehabilitation may be recommended after lumbar discectomy. Some evidence has shown faster pain relief and disability when the exercise programs were started at 4-6 weeks postsurgery as compared to no treatment. Similarly, higher-intensity exercise programs were shown to be more helpful for earlier pain relief and improvement in disability than low-intensity programs.[17]

Of the different techniques currently available, open discectomy with or without the use of an operating microscope remains the most common technique against which the outcomes of other less-invasive surgical techniques are compared. The most common variation of lumbar discectomy involves a minimally invasive approach. For example, a muscle-splitting paramedian exposure of the lateral lamina and medial facet can be accomplished by sequential dilation with various sized tubes that act as a retractor.

An alternative transspinous minimally invasive approach uses the natural corridor through the spinous process without need for muscle splitting or destruction.[18] There is little evidence that minimally invasive techniques offer superior clinical results, but they usually require a smaller incision and can result in less blood loss.[19, 20]

After the patient is positioned, the operative site is radiographically localized. An intraoperative crosstable lateral radiograph is used to identify the skin incision for the appropriate level. The proposed midline incision site is marked and the surgical field prepared and draped. The incision site is infiltrated with 1% lidocaine mixed with 1:100,000 epinephrine. A midline skin incision is made with a No. 10 scalpel along the previously marked incision. The dissection of the subcutaneous tissues is completed using the monopolar electrocautery.

The subcutaneous tissues are retracted using self-retaining Weitlaner retractors. The lumbodorsal fascia is then identified and opened along the spinous process just off the midline using the monopolar electrocautery. At this stage, the desired spinal level should be confirmed with intraoperative radiography.

The paraspinous muscles are stripped from the spinous processes using a subperiosteal technique down along the lamina to the edge of the facets either bluntly or with monopolar cautery. For a discectomy, exposure to the medial edge of the facet joints is generally adequate. Further lateral dissection can damage the capsule of the facet joint and can potentially lead to instability at that level. At this stage, a self-retaining retractor is used to maintain the exposure. The surgical level can again be confirmed before proceeding with bony removal.

The microscope covered with sterile drapes is brought into the field at this stage. The ligamentum flavum is detached from the inferior surface of the lamina using an angled curette, and a hemilaminotomy is then performed using the combination of the high-speed drill and Kerrison rongeurs. Some undercutting of the medial aspect of the facet joint may need to be performed to achieve adequate lateral exposure to the nerve root and underlying disc.

The thecal sac, along with the nerve root, is then retracted medially, and the underlying disc surface can be seen. The posterior longitudinal ligament and annulus fibrosus is then cut using a No. 11 or 15 scalpel. After cutting open the annulus, disc material may begin to extrude and can be removed using pituitary forceps. When placing the pituitary into the disc space, care must be taken not to insert too deep in case of an incompetent anterior longitudinal ligament that could result in injury to the iliac vessels. Up- and down-angled curettes can be used to help release residual disc fragments or tamp down a central disc bulge.

After the surgeon is satisfied that an adequate amount of disc has been removed, the thecal sac and the nerve root is inspected for residual compression and CSF leak. Some surgeons place steroids (40 mg of methylprednisolone acetate [Depo-Medrol] or 4 mg dexamethasone [Decadron]) over the nerve root at this stage to decrease postsurgical inflammation. Placement of a free fat graft over the thecal sac has also been attempted to prevent adhesion formation. The fascial layer is closed using 2-0 Vicryl, which is important to prevent wound breakdown. The skin layer is closed with a subcuticular 4-0 Monocryl, staples, or skin glue.