Minimally Invasive Lumbar Diskectomy

Minimally invasive techniques have revolutionized the management of pathological conditions in various surgical disciplines and more recently have been applied to the field of spine surgery. One of the most commonly performed procedures is minimally invasive microdiskectomy. Using a muscle-dilating approach, this procedure reduces the iatrogenic soft tissue injury that occurs with routine exposure of the spine. This chapter details the minimally invasive microdiskectomy procedure, including patient selection, operative techniques, complication management, and postoperative care.

42.2 Patient Selection

As with all spinal surgical procedures, proper patient selection begins with a detailed history and physical examination, as well as a judicious review of the radiographic imaging. Once it has been established that the patient has a symptomatic herniated disk, management options should be discussed with the patient. Many patients who have pain from an acutely herniated disk can be satisfactorily treated without surgery. These patients will frequently notice significant improvement after a trial of nonsteroidal anti-inflammatory medication, muscle relaxants, oral steroids, or some combination of these. ¹ Physical therapy can also be helpful in ameliorating the pain, particularly in the subacute period. In patients who do not respond to these modalities, epidural steroids can often provide significant pain relief and are commonly given in sets of three. Surgical management should be reserved for patients for whom 6 to 12 weeks of nonoperative therapy have failed or who have a significant motor deficit caused by the disk herniation. The potential risks and complications of the procedure should be explained to the patient, including, but not limited to, nerve root injury, paralysis, back pain, leg pain, failure of symptom relief, neurologic worsening, cerebrospinal fluid (CSF) leakage, spinal instability, reoperation, disk reherniation, infection, spinal instability, and the risks of anesthesia. ²^, ³

42.3 Preoperative Preparation

Minimally invasive microdiskectomy can be performed using epidural anesthesia, but most surgeons prefer to have the patient placed under general anesthesia. ⁴ One large-bore intravenous line is usually sufficient, and arterial lines are not normally placed in healthy patients. Intravenous antibiotics should be given before skin incision is done: cefazolin 1 g or vancomycin 1 g in patients who are allergic to penicillin. Compression stockings and thromboembolic disease (TED) hose should be applied prior to turning the patient into the prone position. A Foley catheter is generally not used because the surgery time is usually fairly short. The patient is then carefully turned into the prone position onto a Wilson frame. The frame should be cranked up to encourage flexion of the spine and opening of the interspace. All the pressure points should be appropriately padded, particularly the ulnar regions and the eyes. The anesthesiologist should check the patient’s face every 15 minutes for any signs of compression. The lateral C-arm fluoroscope should be brought into the field, preferably from the side of the patient that is opposite the operating microscope. The patient is then prepared and draped in the usual sterile fashion, and the fluoroscope and microscope are also draped at this time.

42.4 Operative Procedure

The universal arm bar is mounted to the bed frame, and the flexible retractor is attached to the arm bar. The location of the surgical level is determined by inserting a 22-gauge spinal needle into the paraspinal soft tissue under fluoroscopic guidance. This is a key step because it will determine the position of the tubular retractor. An 18-mm skin incision created 15 mm lateral to the midline is then centered over this point. The Bovie cautery (Bovie Medical Corporation, St. Petersburg, Florida) is used for hemostasis and to dissect through the dermal layer. A Kirschner wire (K-wire) is passed through the incision and centered on the disk space of interest ( ▶ Fig. 42.1). The wire is inserted through the fascia and then the initial dilator is passed over the wire and docked on the lamina–facet junction ( ▶ Fig. 42.2 a). The wire should not be used to dock on the spine because it could inadvertently pass through the interlaminar space and cause a CSF leak or nerve root injury. Once the location of the dilator is confirmed with fluoroscopy, the K-wire is then removed from the field. Controlled forceful sweeping movements of the dilator in the cephalad–caudad and lateral–medial directions are then used to scrape the paraspinous musculature off the bony structures at the tip of the dilator ( ▶ Fig. 42.2 b). Incrementally larger dilators are sequentially passed over the initial dilator and advanced to the laminar–facet junction ( ▶ Fig. 42.3, ▶ Fig. 42.4). The numerical reading on the side of the final dilator is used to determine the appropriate tubular retractor length for the patient, ranging from 3 to 10 cm long. The diameter of the tube ranges from 14 to 26 mm, although 16- or 18-mm-diameter retractors are most commonly used for microdiskectomy. The appropriately sized tubular retractor is then passed over the final dilator. A variety of different medical device companies provide slightly different versions of the retractor; essentially, there is no functional difference between the various options. The tubular retractor should be docked on the lamina facet junction such that a small portion of the interlaminar space is visible inferiorly. Once the proper tube position is radiographically confirmed, the tube is locked into position with the flexible retractor arm, and the dilators are removed ( ▶ Fig. 42.5). The remainder of the procedure can be performed using loupe magnification, the endoscope, or the operating microscope, and the surgical technique is identical for any of these methods.

Fig. 42.1 (a) After localizing the skin incision using a 22-gauge spinal needle, the K-wire is inserted through the skin, centered on the disk space. (b) Fluoroscopic image demonstrating the K-wire in place after penetrating the fascia.

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