Lumbar Microdiscectomy/Laminotomy

Microdiscectomy or microlaminectomy are procedures performed to relieve pressure on a nerve due to a herniated disc or narrowing in the spinal canal.

The decision to perform a microdiscectomy is based on three factors: Patient's symptoms, findings on physical exam, and radiographic abnormalities.

A. PATIENT SYMPTOMS

The patient's symptoms are generally categorized into three patterns of pain. Axial pain is that which occurs along the spine and the overlying musculature. Referred pain is that which occurs along the buttocks or pelvic region. Radicular pain is that which extends partially or completely along the length of the leg.

Axial pain is generally vague and is typically similar irrespective of the underlying problem. Referred pain into the pelvis or buttocks is also generally vaguely defined. These patterns of pain may be due to irritability of small nerves along the surface of discs or joints and it is difficult to differentiate these patterns of pain from soft tissue inflammation such as ligamentous injuries or tendonitis. Instability of joints or vertebrae in the lumbar spine can also produce similar patterns of referred pain. Radicular pain typically conforms to a specific nerve root distribution or course. A radicular pattern of pain is most easily identified as specifically related to nerve root impingement and, as such, is generally most accurately correlated with a specific abnormality within the spine.

Ideally, symptoms of radicular pain are clearly present and are greater than patterns of referred or axial pain.

B. PHYSICAL FINDINGS

Physical findings can generally be divided into three groups:

Limitation of motion, the presence of tenderness, and neurological deficits. While limited range of motion in the lumbar spine is frequently present, it is a very nonspecific finding and does not reflect any particular abnormality which would suggest an indication to perform a microdiscectomy. Tenderness is also frequently present and may be diffusely noted along the musculature, joints, and is usually present over the sciatic notch in patients with complaints of sciatic nerve irritation. The sciatic notch is located in the lower buttocks and is the point origin of the sciatic nerve from the pelvis. Tensions signs, such as the straight leg-raising maneuver, are another method of eliciting tenderness in the patient. These techniques involve stretching the affected nerve and recreating the symptomatic leg pain. In lumbar disc abnormalities, these generally include the femoral stretch test, which elicits pain along the femoral nerve, and the straight leg raise, which elicits pain along the course of the sciatic nerve.

Neurological deficits are the most specific indicator of nerve root compression. Neurological deficits include loss of a specific reflex, loss of sensation in a specific area correlating with a particular nerve, or loss of strength in a muscle or muscles conforming to a particular nerve.

In general, patients are usually not considered for surgical treatment until a period of six to eight weeks of nonoperative care has been attempted. This treatment would generally include restricted activity, physical therapy or chiropractic treatment, anti-inflammatory medication, narcotic analgesics and muscle relaxants, and possibly epidural cortisone injections. Several factors may indicate a need for more expeditious surgical treatment. These factors would include incapacitating unremitting pain, progression of a neurological deficit posing a potential functional impairment, or development of bowel or bladder dysfunction.

C. RADIOGRAPHIC ABNORMALITIES

Indications for surgical treatment radiographically would include the presence of a herniated disc on MRI, CT scan, or myelography. The herniated disc should be of sufficient size that it is placing pressure on a specific nerve root or displacing the position of the nerve root. Inorder for the herniation to be deemed significant, it should be compressing upon a nerve root, which correlates with the patient's pattern of pain, and physical findings. Multiple studies have indicated that as many as 25-30 of asymptomatic patients may have herniations noted on MRI and CT scan. As such, it is common that patients will be noted to have incidental herniations present. The presence of a disc herniation should only be considered the source of a patient's pain when it correlates with the clinical symptoms and physical findings.

II. SURGICAL TECHNIQUE

The basis for any microsurgical procedure is the use of magnification and bright illumination of the operative field. This can be provided to a satisfactory degree by use of an operative microscope, operative magnifying loupes, and fiberoptic head lamp. The primary advantage of microsurgery is a reduction of tissue trauma, a decrease in operative recovery, and a reduction of postsurgical scarring and operative trauma. A number of techniques, such as micro endoscopic visualization and laser assisted disc resection have been employed. While these techniques may be of benefit in selected patients, they have not been shown to substantially change or improve the fundamental microdiscectomy procedure. Microsurgery can be performed at one or more levels, either unilaterally (one side), or bilaterally (both sides). Obviously, the primary benefits diminish as the number of levels increase due to the exposure necessary to address each level.

The basic unilateral, one level microdiscectomy for a herniated disc is performed as follows. An approximately 1 inch or less incision is made, overlying the disc space in the skin as determined by an intraoperative

x-ray. The fatty tissue beneath the skin is then divided to the dorsal fascia which is the thick tissue overlying the muscle above the spine. This fascia is then incised and the musculature swept to the side revealing the underlying bone and ligaments. The spinal canal is entered by resection of the ligamentum flavum which is the ligament connecting between the lamina of each vertebra. The lamina are the flat areas of bone overlying the top of the canal at each level. A small portion of the edge of the lamina above and below may also be resected with the ligaments to allow adequate exposure of the underlying nerve root and disc . Once the canal has been exposed, the nerve root overlying the disc identified and gently moved to the center of the canal and held with a retractor. The herniated disc can then be visualized . Small veins are coagulated to minimize bleeding. The thin veil of ligaments overlying the herniation is incised and probes are used to dislodge the nuclear material . This material is then removed with graspers until the nucleus is noted to be empty of any free fragment material . Typically, the majority of the volume of the disc is left with removal of only the loose fragments. Once verification has been assured that the disc herniation has been removed and no further pressure exists on the nerve root, the retractors are removed . A small piece of fat is usually placed over the surface of the nerve to prevent adhesions. More recently, a number of synthetic materials have been made available which provide this same function. The tissues are then closed in three layers, the muscle fascia, the subcutaneous fat, and the skin. Most frequently, the skin is closed under its surface using a subcuticular suture.

III. POST-OPERATIVE COURSE

Patients are generally maintained at bedrest for several hours following the surgical procedure. They are typically advanced to ambulation on the day of surgery. Patients are usually advanced to a regular diet on a gradual basis and IV fluids are discontinued when they are able to accept liquids. IV antibiotics are usually given pre-operatively and for 24 hours

post-operatively. If the patient is independent with ambulation, able to tolerate a regular diet, and afebrile and able to void they are generally discharged on the day of surgery. Patients may occasionally be discharged on the day following surgery. Average length of stay in 275 patients has been 1.2 days.

Patients are advised at the time of discharge to avoid activities such as bending, lifting, and vigorous twisting. They are instructed on body mechanics or techniques in sitting, standing, and transferring out of bed, etc. Patients are typically prescribed pain medication to be taken by mouth as needed and occasionally anti-inflammatory medication for residual nerve root swelling and irritation.

Patients are generally advised to refrain from getting the incision wet for three days postoperatively. At that time they may shower. It is generally advisable to avoid submerging the incision in a tub or pool for at least one week.

Follow-up examinations are typically conducted at one week, one month, and three months post-operatively.

At approximately one month post-operatively patients are referred for physical therapy. This includes a graduated course of lower extremity and lumbar flexibility, strengthening, and instructions on body mechanics and postural alignment. Patients are generally advised to increase their recreational and daily activities commensurate with their progress at physical therapy.

IV. OUTCOMES

A. BENEFITS

Appropriately selected patients, as previously described, can generally expect approximately an 80-90 likelihood of improvement, if not relief, of radicular pain following microdiscectomy. Our surgical procedures have resulted in a success rate of 89 good or excellent outcomes in 275 cases.

Although relief of leg pain is common, relief of back pain to the same degree is less predictable. Although the majority, approximately 70-80 of patients can expect improvement or substantial relief of back pain, some patients may experience continued back pain of a substantial degree. This most likely represents damage to the disc unassociated with pressure on a nerve root.

B. COMPLICATIONS

Operative risks include infection, bleeding, neurological injury, recurrent herniation, and late instability.

Post-operative infection rates for all surgical procedures performed vary on a national basis between 1 and 2. We have experienced an infection rate of 1/275 = .4 following microdiscectomy procedures.

Bleeding associated with a microdiscectomy is almost without exception negligible. Although the potential exists for enormous blood loss if one of the great vessels anterior to the disc space were injured, this event is fortunately exceedingly rare. There have been no instances of excessive blood loss or need for transfusion in microdiscectomies we have performed.

Neurological injury is an unlikely operative complication. The exact incidence of permanent neurological injury is unknown although it is probably on the order of less than 1%. Most frequently, postoperative neurological deficits were present pre- operatively. Occasionally, transient weakness or sensory change may be noted postoperatively due to traction, compression, or swelling of affected nerve roots. These conditions are typically temporary and usually resolve in a matter of days or weeks. One patient has experienced an inability to void following surgery without specific neurological injury noted .4 (1/275).

Recurrent herniations have been noted in 5-10 of cases based on the literature. Our known recurrence rate has been 5.4 (15). Thirteen of these patients have returned for surgery and 11(85) have had successful outcomes following surgery.