Introduction
Acute back pain can be severe and debilitating, and if not appropriately treated, can lead to recurrent symptoms in the majority of paitents. One of the leading causes of back pain is intervertebral degeneration that can lead to degenerative disease and disc herniation. Disc herniation results from a localized displacement of the nucleus pulposus beyond the margins of the intervertebral disc space. Treatments for disc herniations include conservative medical management and physical therapy. More interventional approaches can also be considered, including epidural or transforaminal steroid injections ; however, when symptoms are resistant to these measures, more invasive interventions including discectomy and surgery can be considered to remove the herniated disc. ,
Although there is controversy over the superiority of surgical intervention versus conservative management, roughly 40% of patients receiving conservative management will eventually undergo a surgical intervention to treat the herniated disc. , When surgical intervention occurs, nearly 18% of patients will experience a recurrence of the disc herniation, which is defined as a pain-free period of minimum of 6 months with herniation at the same level, and 80% of these patients will undergo a second operation. Though neither discectomy nor surgical management has been found to be superior, the question to continue conservative measures and tolerate the symptoms, or proceed with discectomy or surgical intervention remains a predicament to both the patient and the physician. If discectomy is determined to be the treatment method, several different techniques can be considered. In this chapter, we will explore the indications, clinical applications, technical approaches, and complications for minimally invasive discectomy techniques for the treatment of disc herniations.
Relevant anatomy
The intervertebral disc is composed of an outer annulus fibrosus with an inner nucleus pulposus that is the site of collagen secretion; it consists mainly of type II collagen, which accounts for 20% of its dry weight ( Fig. 4.1 ). The nucleus pulposus contains proteoglycans that retain water to provide cushioning to resist axial compression of the spine. , The purpose of the annulus fibrosus, which is composed mainly of type I collagen, is to maintain the central location of the nucleus pulposus. , , The spinal canal or foraminal space can be become narrowed when (1) there is disc protrusion causing possible impingement of the thecal sac or exiting spinal nerve roots when an entire disc protrudes with an intact annulus fibrosus; (2) the nucleus pulposus protrudes through a disrupted annulus fibrosus; or (3) the nucleus pulposus protrudes and breaks off as a free segment ( Fig. 4.2 ).
Biological factors that increase the risk of disc herniation include reduction of water in the nucleus pulposus, increase in the amount of type I collagen in both the nucleus pulposus and annulus fibrosus, degradation of collagen and extracellular matrix, and an upregulation of matrix metalloproteinase and inflammatory pathways. , , Up to 75% of individuals affected by disc herniation are estimated to be predisposed to the condition as numerous genes are involved in weakening and changing the structures involved in disc herniations. Aside from biologic and genetic factors, disc herniations can result from axial overloading without any predisposing factors or degeneration. Without predisposing factors, the herniation of discs can occur from spinal overloading, especially from static overloading, which increases risk for posterior disc herniation. The static overloading may be the culprit in the increasing prevalence of disc herniation in sedentary, younger individuals who spend most of their time in the seated position.
The most common area for disc herniations is the lumbar spine followed by the cervical spine with the thoracic region having the lowest incidence of disc herniation. The discs are more likely to herniate posterolaterally where the annulus fibrosus is thinner and lacks the support from posterior longitudinal ligament ( Figs. 4.2 , 4.3 ). Additionally, lumbar roots are not protected from impingement from herniation by the bony wall of the facet joints as cervical joints are, and the nuclear material is more posterior than its cervical counterparts ( Fig. 4.4 ).
Clinical presentation and diagnosis
The symptoms of disc herniation include radicular pain, sensory abnormalities in a dermatomal distribution, weakness in the distribution of one or more nerve roots, focal paresis, limited flexion, and pain associated with increased intraabdominal/thoracic pressure. , When the herniation is paracentral, the traversing nerves roots are affected. In contrast, when it is a far lateral herniation, the exiting nerve root can be affected.
Diagnostic criteria for lumbar disc herniation was recommended by the Lumbar Disc Herniation with Radiculopathy Work Group of the North American Spine Society’s (NASS) Evidence-Based Guideline Development Committee to consist of manual muscle testing, sensory testing, and supine leg raise test as the gold standard for diagnosis. Other recommendations include screening with the straight leg test, and if three of the four symptoms are present (dermatomal pain, sensory deficits, reflex deficits, and motor weakness), then a diagnosis of lumbar disc herniation can be made. Plain radiographs are also commonly performed as a first-line imaging modality for back pain with findings such as narrowed intervertebral space, presence of traction osteophytes, and compensatory scoliosis indicative of disc herniation. MRI, however, is the gold standard to confirm a disc herniation with an accuracy of 97%. , Findings include enhanced T2-weighted signal from the posterior 10% of the disc diameter.
Conservative treatment
Conservative medical management of disc herniations is often multimodal and includes antiinflammatory medications and physical therapy, with hopeful resolution weeks after the onset of symptoms. Though often prescribed, limited evidence exists for the use of muscle relaxants and oral corticosteroids. When symptoms last for >6 weeks, translaminar epidural steroid injections, a second-line treatment, can be considered. Though reductions in pain and function can be immediate, often the benefits are limited in duration, and patients require repeated injections with minimal effect on the long-term risk of surgery. , Epidural steroid injection can also be considered, but the long-term benefits may be limited. Even if these methods improve symptoms, the risk of disc reherniation is elevated and is increased by the following risk factors: diabetes, advanced age, smoking, trauma, preoperative disc height index, disc sequestration, longer duration of sick leave, workers’ compensation, and greater preoperative symptom severity.
Minimally invasive treatment
If conservative and epidural injections fail, operative management can be considered; although this has short-term benefits, benefits in the long term are conflicting. , , Interestingly, various factors can predict successful outcomes after discectomy, and include severe acute preoperative low back pain, increased preoperative physical activity, younger age, shorter symptom duration, mental health status, and higher preoperative leg pain severity. , , , An invasive surgical method, the open discectomy, has demonstrated efficacy in treating lumbar disc herniations. , Based on the herniation location (paracentral or far lateral), different approaches can be considered. The paracentral approach results in longer incisions, more muscle stripping, and is limited due to the difficulty in accessing far lateral discectomy. For far lateral, the Wiltse paraspinal approach can be performed. As with all forms of surgical intervention, minimally invasive techniques for discectomy have been increasingly utilized over the past years.
Minimally invasive techniques used by interventional chronic pain specialists have been found to be associated with a reduction in length of hospital stay, less trauma to the tissue and bones, and lower acute care charges. When compared to open discectomy, these minimally invasive techniques result in a decreased operative time, less blood loss, fewer complications, lower reoperation rates, and fewer infections. Minimally invasive techniques include percutaneous discectomy automated technique and laser-assisted technique, percutaneous laser-assisted annuloplasty, minimally invasive lumbar decompression procedure, and percutaneous endoscopic lumbar discectomy performed via the transforaminal or interlaminar approach. The following sections will summarize each approach with associated complications.
Percutaneous discectomy: Automated technique
Percutaneous discectomy using the automated technique is indicated for patients with low back and radicular pain caused by a contained disc protrusion who have failed medical management ( Figs. 4.5 , 4.6 ). To perform the technique, the patient is positioned in the lateral or prone position with slight flexion of the lumbar spine, which can be assisted by placing a pillow under the abdomen. The spinous processes of the vertebra to be targeted are identified under fluoroscopic view. The skin is cleaned antiseptically and anesthetized below and laterally 3.8 cm from the spinous processes. A small stab wound is made to allow for the introducer cannula. Under fluoroscopic guidance and sequential imaging, the cannula with the stylet is advanced to the middle of the disc to be decompressed ( Figs. 4.6 , 4.7 ). Since the somatic nerve roots are in close proximity, if any paresthesias are elicited, the introducer should be redirected more cephalad. Special care must be taken to not advance the needle completely through the disc or into the lower limits of the spinal cord or cauda equina. If advanced too laterally, the needle can enter the lower pleura or retroperitoneum. With the cannula in the center of the disc, the stylet is then removed, and contrast is injected to assess for any annulus abnormalities ( Fig. 4.8 ). The decompressor probe is then advanced until it exits the cannula. The probe is activated for 15 seconds at a time for a maximum total of 5 minutes. The probe can then be slowly advanced to the anterior annulus without impinging on it. After sufficient disc has been removed, the probe can be withdrawn.
Associated complications
Complications tend to be self-limited. Discitis, which can be difficult to treat due to the limited blood supply to the disc, can occur, and presents with spine pain days to weeks after the procedure. Epidural abscess can occur 24–48 hours after the procedure and presents with fever, severe back pain, and neurological deficits. Both complications require further investigation with urine and blood samples, initiation of empiric antibiotics, and emergent MRI for possible drainage. Rarely, pneumothorax can occur, but it is typically limited with the use of fluoroscopic techniques. If small in size, pneumothorax can be treated conservatively, but if significant, it may require placement of a chest tube. Retroperitoneal organ damage can occur but is minimized with fluoroscopic visualization during the procedure. Finally, spinal cord damage can occur if the needle goes through the entire disc, and nerve root damage can occur if the needle is advanced too laterally.
Percutaneous discectomy: Laser-assisted technique
Percutaneous discectomy using the laser-assisted technique is indicated in patients with low back and radicular pain caused by disc protrusion. This technique vaporizes portions of the herniated disc with energy derived from the laser in an attempt to reduce intradiscal pressure ( Fig. 4.9 ). Like percutaneous discectomy using the automated technique, patients must have failed conservative management and epidural steroids with some chronic pain specialists recommending a trial of transforaminal epidural steroid injection. However, unlike percutaneous discectomy using the automated technique, computed tomography (CT) is preferred over fluoroscopic guidance, as CT can demonstrate the vaporization of the nuclear material. Positioning is similar to the automated technique. Several CT images are first taken near the disc to be treated to assess the positions of the surrounding structures. The skin over the lumbar paraspinous regions is prepared antiseptically and anesthetized. The introducer is then inserted and directed under CT guidance toward the annulus and posterior disc to be treated, with needle placement confirmed by CT ( Fig. 4.10 ). Once in the proper place, the fiberoptic cable is placed through the introducer and advanced until it exits and extends beyond the introducer by approximately 5–6 mm. The settings for the vaporizer are 15–20 W delivered in 0.5–1.0 second pulses at four 10-second intervals with a total dose of 1200–1500 J.
Associated complications
Complications are similar to percutaneous discectomy using the automated technique and include discitis, epidural abscess, pneumothorax, and spinal cord and nerve root injury. Osteonecrosis has been reported of the adjacent vertebral body and is more often seen when a side-firing potassium triphosphide or holmium:yttrium-aluminum-garnet laser is used. It is less frequent when a direct-firing neodymium-doped yttrium-aluminum-garnet laser is used.
Percutaneous laser-assisted annuloplasty
Percutaneous laser-assisted annuloplasty is indicated in patients with lumbar discogenic pain secondary to an internally disrupted disc or limited herniation that fails to respond to medical management and epidural steroid injections. It is believed to cause pain relief via destruction of annular nociceptive fibers, thermal injury to the annulus with healing afterwards, and reduction of disc volume and pressure. It is not indicated in patients with spinal stenosis or disc herniation with nerve root impingement.
The patient can be positioned in the prone or lateral position based on the choice of the chronic pain specialist. If prone positioning is chosen, then the patient can be placed in a partially oblique position with a foam wedge. The skin is then prepared and anesthetized, and the inferior end plate of the affected spinal level is located under fluoroscope guidance. The fluoroscope beam is rotated to locate the superior articular process, and the beam is aligned to the middle-inferior aspect of the end plate. The needle should enter the skin lateral to the middle of the superior articular process and advanced anterior to the midpoint of the superior articular surface and parallel to the endplates. Additional anesthetic can be injected at this time to assist with procedural discomfort. The introducer is inserted parallel to the needle, advanced into the posterior annulus, and the tip location confirmed by taking fluoroscopic images in multiple planes.
Discography should then be performed to locate the exact area to be treated and determine annular abnormalities. This can be done with 0.3 mL of contrast mixed with 0.3 mL of sterile indigo carmine, which will highlight the diseased annular ring ( Fig. 4.11 ). Finally, after endoscopic assessment and under fluoroscopy, the fiberoptic cable is then introduced into the subligamentous portion of the posterior annulus ( Fig. 4.12 ). The settings for the holmium:yttrium-aluminum-garnet laser should be set between 0.5 and 1.2 J to provide up to 11,000 J. Depending on the experience and preference of the chronic pain specialist, intradiscal antibiotics and/or steroids can be injected prior to full removal of the introducer.
