Lumbar Discectomy Using a Tubular Retractor System

Naderafshar Fereydonyan

Shyam A. Patel

D. Greg Anderson

Lumbar microdiscectomy is the most commonly performed spinal operation (4). In 1909, Oppenheim and Krause described the removal of a herniated lumbar intervertebral disc using a midline posterior lumbar transdural approach, though they misunderstood the pathology and believed the disc herniation was a type of tumor (chondroma) (25). In 1934, Mixter and Barr (23) described the cause/effect relationship between lumbar disc herniation and sciatica. As surgical techniques evolved, extradural hemilaminectomy became the standard approach for retrieving herniated lumbar disc fragments. In an effort to improve surgical outcomes, there has been a general interest in reducing the iatrogenic surgical trauma to the muscles, ligaments, and joints surrounding the surgical site.

Over the years, there has been a trend toward less invasive surgical techniques for the treatment of lumbar disc herniations. Caspar and Yasargil separately described the concept of microdiscectomy in the 1970s (7,37). Kambin (17) used a modified arthroscope to perform lumbar discectomy. Foley and Smith (12) designed the microendoscopic (MED) system for lumbar discectomy in 1997. The second generation of the MED system was developed in 1999, allowing surgeons to address migrated herniated disc fragments and lateral recess stenosis (40). Various tubular retractor systems have been introduced in recent years, allowing microdiscectomy to be performed through progressively smaller surgical incisions. At least as equal in importance to the development of tubular retractor systems has been the improvement in viewing options including surgical endoscopes and operative microscopes. Using modern tubular retractor systems and surgical microscopes, the removal of herniated disc fragments has become a routine minor operation, commonly performed on an outpatient basis.

CLINICAL PRESENTATION

Symptoms

The most common symptoms of a lumbar disc herniation include radiating pain from the lumbar area to one or both extremities (following a dermatomal distribution), numbness or paresthesias, and muscle weakness. The symptoms generally begin abruptly; however, some patients may describe an evolution of pain in the lumbar spine, which progresses into the leg over a period of time. The symptoms may begin following some inciting event or during the course of normal daily life. In rare cases, patients may develop symptoms of saddle anesthesia and sphincter disturbance (cauda equina syndrome), which is considered to be a surgical emergency.

Physical Examination

The physical examination begins with a general inspection of the patient, which includes the gait and posture. Patients with severe radicular pain may avoid significant walking or present with a slightly flexed or side bent posture. Muscle spasm may be present in the acute phase of sciatica. The straight leg raise test (hip flexion with knee extension) may increase or reproduce the sharp, lancinating leg pain (10). A detailed neurologic examination is of paramount importance and should include motor, sensory, and reflex testing. Patients with symptoms of possible cauda equina syndrome should undergo rectal examination.

DIFFERENTIAL DIAGNOSIS

Many conditions may mimic the presentation of a lumbar disc herniation. The differential diagnosis includes tumors of the spinal column or neural elements, various forms of peripheral nerve pathologies (diabetic, entrapment, etc.), osteoarthritis of the lower extremity, instability of the lumbar spine, and spinal infections or fractures.

DIAGNOSIS AND IMAGING

The MRI is the imaging modality of choice for the evaluation of the lumbar spine in the setting of a patient suspected to have a lumbar disc herniation. It is important to know, however, that a considerable percentage of asymptomatic individuals will have abnormalities on lumbar MRI; hence, the symptoms and MRI findings must be carefully correlated (6).

For patients with contraindications to an MRI, CT myelography is an acceptable alternative (19). Plain radiographs, including dynamic flexion/extension films, are helpful in the diagnosis of lumbar instability or abnormalities of the lumbosacral segmentation.

In questionable cases or those with other related disease processes (e.g., diabetic patients), electromyography may also be helpful.

INDICATIONS

Most patients with symptomatic lumbar disc herniations will respond to nonsurgical treatment. In patients with acute, severe symptoms, a short course of bed rest (24 to 48 hours) may be helpful. Short-term oral analgesic medications may be used to control severe pain. Nonsteroidal anti-inflammatory drugs are often helpful in reducing symptoms. Less frequently, patients may require a short course of oral corticosteroids. In patients who fail to respond to initial treatments, lumbar epidural steroid injections may be considered. These procedures have been shown to reduce radicular symptoms in many patients (5). Some studies have suggested that patients who respond temporarily to a lumbar epidural steroid injection are more likely to have a favorable outcome with surgical treatment (31). Physical therapy, chiropractic treatment, and acupuncture have been promoted as treatment options for acute sciatica, although the quality of the data supporting these interventions is suboptimal.

The indications for a microendoscopic discectomy using a tubular retractor system are identical to those for a traditional open microdiscectomy. Patients with cauda equina syndrome or profound and severe and progressive motor weakness should be treated surgically in an urgent fashion (1,18,28).

The most frequent indication for surgery in the setting of a lumbar disc herniation is leg pain symptoms, which fail to respond adequately to nonsurgical care. Most experts agree that severe leg pain that has not responded adequately to a 6-week course of nonsurgical care constitutes a reasonable indication for surgical intervention. Other indications such as isolated sensory loss and isolated lower back pain in the setting of a lumbar disc herniation do not have substantial evidence-based support for a surgical approach at the current time.

Contraindications and Special Situations

Although there are no absolute contraindications to lumbar discectomy with a tubular retractor system, certain situations are best approached by experienced hands.

For example, compared to nonobese patients, morbidly obese patients present a greater technical challenge, although the theoretical advantages of a smaller surgical dissection in this patient population are substantial. Morbidly obese patients require the surgeon to consider the distance from skin to spine relative to the length of the available retractor system. Open field MRI may allow the surgeon to measure this distance during the preoperative planning session. Most tubular retractor systems have maximal lengths of 90 to 100 mm. Distances from skin to spine that are longer than
this will require a “cut down” in order for the tube to be docked on the spine. Although the difficulty of such a case is increased, in experienced hands, the efficacy of a minimally invasive approach is supported in the literature (36).

Revision discectomy presents another technical challenge. Due to adhesions, the rate of dural tear is increased regardless of the surgical approach. Again, with experience, revision surgery is feasible; however, such cases are not recommended for surgeons early in the learning curve of tubular retractor-based surgery (22).

ADVANTAGES AND DISADVANTAGES OF USING A TUBULAR RETRACTOR SYSTEM

The primary goals of microdiscectomy using a tubular retractor system are not different from those of a traditional open microdiscectomy. It is critical that the surgeon achieve adequate decompression of the neural elements and remove all free disc material regardless of the approach. Using a tubular retractor system, surgery can theoretically be done with less dissection of the paraspinal soft tissues, reduced retractor pressure, more sparing of multifidus muscle, and a reduced devascularization of the area (16). Multiple studies regarding tubular-based microdiscectomy have suggested advantages of this approach including decreased postoperative pain, more rapid postoperative mobilization, decreased hospital stay, decreased narcotic usage, decreased surgical blood loss, and a quicker return to work or normal activities (9,14,40). Schick et al. (32) reported less root irritation during tubular retractor-based microdiscectomy compared to open microdiscectomy using intraoperative EMG monitoring. Arts et al. in a randomized clinical trial compared muscle injury between tubularbased microdiscectomy and conventional microdiscectomy. In this study, they measured the crosssectional area of the multifidus muscle following surgery and failed to find a significant difference between the groups (2).

The steep learning curve of microdiscectomy using a tubular retractor system has been proposed as a potential disadvantage of the procedure. During the learning curve phase, a surgeon should anticipate longer operative times and potentially higher complication rates. Nowitzke et al. and Rong et al. have suggested that the length of the learning curve is approximately 30 cases, although it is logical to assume that various surgeon-related factors may affect this length (24,29).

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