Introduction
Lumbar intervertebral discs are complex structures subjected to significant axial compressive forces. Because of biomechanical demands and the inability to remodel as a result of an avascular nature, lumbar disc herniation (LDH) is a relatively common cause of back pain and/or leg pain. The clinical course of LDH is often favorable and many patients improve with conservative treatment. Yet LDH can induce significant radicular symptoms or weakness, which may lead to permanent neurological dysfunction, thus necessitating surgical intervention. Approximately 300,000 lumbar discectomy procedures are performed each year in the United States. The etiology is multifactorial, with family history, obesity, and heavy lifting being implicated. Isolated trauma or injury has not been found to be a consistent risk factor, occurring in only 0.2% to 10.7% of adults with a herniation.
From a pathophysiology perspective, LDH results from degeneration of the intervertebral disc constituents, causing disc dehydration and inability to resist axial compression of the spine. Several different surgical techniques have been used to manage LDH including open discectomy (with or without the use of a surgical microscope), automated percutaneous discectomy, minimally invasive tubular endoscopic discectomy, and chemonucleolysis. The clinical outcome for these procedures is generally favorable with 65% to 90% of patients undergoing surgery reporting good or excellent results. Several studies have demonstrated improved clinical outcomes with surgery compared with conservative treatment.
Despite these favorable outcomes, a number of patients who initially respond well to surgery have a return of symptoms similar to their preoperative state because of a recurrence of herniated disc material at the prior surgical site. The reported incidence of recurrent LDH ranges from 2% to 25%. When it occurs, recurrent herniation is a major contributor to debilitating pain, disability, and the need for reoperation following the primary procedure. It also places a significant burden on the healthcare system. Ambrossi et al. have demonstrated that the mean cost of caring for patients requiring reoperation for recurrent disc herniation to be 39,386 US dollars per patient compared with a mean cost of 2315 US dollars for patients responding to conservative management. In this chapter, we discuss the anatomy and clinical presentation, along with the treatment of LDH, including primary, recurrent, and residual herniation. Additionally, existing literature comparing the various techniques employed for the treatment of LDH is briefly reviewed.
Anatomy
Intervertebral disc consists of an outer annulus fibrosus (AF) and inner nucleus pulposus (NP). The inner NP is composed of type II collagen and proteoglycans that facilitate water retention, producing hydrostatic pressure to resist axial compression. In contrast, the AF functions to maintain the NP within the disc epicenter and is comprised of concentric type I collagen fibers. LDH are classified based on their shape and are a result of displacement of the disc’s inner substance beyond the intervertebral boundaries. Herniations are categorized into three shapes: protrusion, extrusion, or sequestration ( Fig. 8.1 ). Protrusion occurs when the height of the hernia is less than the length of the base. Extrusion is when the height of the hernia exceeds the base and sequestration is when there is loss of continuity between the herniated material and the intervertebral disc. Correlating clinical presentation with radiographic findings is paramount, as LDH position will dictate the surgical approach.
Clinical Presentation
Although the entire pathophysiological response to disc herniation can vary, it is accepted that neural structures surrounding the disc can become compressed and/or mechanically irritated with the resultant chemical inflammation invoking radicular pain and subsequent radiculopathy. Signs and symptoms of LDH include radicular pain, sensory abnormalities, and weakness in the distribution of one or more lumbosacral nerve roots. Focal weakness, restricted trunk flexion, and increased leg pain exacerbated by Valsalva maneuvers are reported. Additionally, increased pain when sitting, attributed to increased disc pressure, is reported.
Physical examination including manual muscle testing, sensory testing, reflex testing, and supine straight leg resistance testing are key components for the clinical diagnosis of LDH. It is of paramount importance to correlate the clinical presentation with the radiographic findings. The affected dermatome is dependent on the spinal level of the herniation in addition to the herniation type ( Fig. 8.2 ). Paracentral disc herniations compress the traversing nerve root, whereas far lateral disc herniations affect the exiting nerve root. For instance, a paracentral disc herniation at L4–L5 causes on L5 radiculopathy, whereas a far lateral herniation at the same level results in an L4 radiculopathy ( Fig. 8.3 ).
Imaging
Plain radiography serves as an initial imaging modality to exclude additional etiologies of low back pain. Orthostatic and dynamic views in flexion and extension provide a thorough evaluation for spinal column alignment and instability. Magnetic resonance imaging (MRI) is the imaging choice to confirm a suspected LDH, yielding a diagnostic accuracy of 97%. Relative indications for early MRI acquisition for suspected LDH (<6 weeks) include neurological motor deficits and cauda equina syndrome. Computed tomography (CT) is also capable of identifying disc herniation but provides an image of inferior quality compared with MRI. The North American Spine Society (NASS) evidence-based guideline development committee recommends CT myelography as an alternative diagnostic tool to MRI in confirming suspected LDH. Instances where CT myelogram is preferable to MRI may occur in the setting of spinal implants, prior fusion constructs, foraminal stenosis, or when MRI is unavailable or otherwise contraindicated.
Operative Management
Operative treatment of LDH has been associated with improved short-term benefits with conflicting medium- to long-term outcomes. These findings are comparable with the 8-year results from the Spine Patient Outcomes Research Trial (SPORT) continued follow-up of the herniated disc randomized and observational cohorts for surgical versus nonoperative treatment of LDH. The authors concluded that surgical patients achieved greater improvement than nonsurgically treated patients, with minimal difference in outcomes in either group from 4 to 8 years. Factors predicting successful outcome after discectomy include preoperative higher leg pain severity, shorter symptom duration, younger age, increased preoperative physical activity, and severe preoperative low back pain. Currently, surgical techniques for lumbar discectomy include open and minimally invasive approaches.
Open Discectomy
Standard open discectomy has long been the conventional approach for the treatment of LDH ( Fig. 8.4 ). Although the paracentral approach has robust use, it is associated with longer incision, increased muscle dissection, and difficulty with far lateral discectomy. The Wiltse paraspinal approach is well accepted for far lateral LDH treatment. Outcome data of open discectomy as a treatment option for LDH are well established, with much of the attention directed toward infection risks. In one large multicentral observational study (1772 patients), independent risk factors identified for infection following discectomy included no prophylactic antibiotic treatment and longer duration of surgery than the mean time (68 minutes).
Tubular Discectomy
Minimally invasive spinal (MIS) techniques for LDH treatment have expanded significantly over the last 2 decades. These approaches afford smaller incisions, less soft-tissue and muscle dissection, and reduced postoperative pain and hospital length of stay, but also have a higher learning curve. MIS techniques are performed through a tubular retractor system using either a microscope or endoscope for visualization, thus referred to as tubular microdiscectomy and percutaneous endoscopic lumbar discectomy (PELD). Surgical access entails localization of the laminofacet junction and sequential dilation of the paraspinal musculature under fluoroscopic guidance ( Fig. 8.5 ).
As a group, MIS approaches are associated with reduced operative time and blood loss without an increase in overall complications when compared with open discectomy. Qin et al. evaluated PELD versus posterior open lumbar microdiscectomy (OLMD) for the treatment of symptomatic LDH and found no statistically significant difference between the two groups in visual analog scale (VAS) scores, Oswestry Disability Index (ODI) scores, complication rates, incidence of recurrence and reoperation, and operative times. However, patients in the PELD group experienced a higher incidence of residual disc or incomplete decompression compared with the OLMD group, but experienced shorter hospital stays and times to return to work. Arts and colleagues provided 2-year results of a double-blind randomized controlled trial evaluating tubular discectomy versus conventional microdiscectomy for the treatment of LDH. The results demonstrated no significant differences between the two methods for Roland-Morris Disability Questionnaire scores for sciatica at 2-year follow-up. When comparing repeat surgery rates, the reoperation rate was higher in the tubular discectomy group (15%) compared with conventional microdiscectomy (10%), although this was not statistically significant ( P =.22).
Wang et al. evaluated interlaminar minimally invasive discectomy (ILMI) compared with conventional microdiscectomy. Results demonstrated significant differences between the two groups in blood loss (95% confidence interval [CI] –1.84 to –0.02; P =.005) and hospital length of stay (95% CI –1.55 to –0.04; P =.04). There were no significant differences noted in short- and long-term back and leg VAS scores, ODI scores, or the incidence of complications. The authors concluded both ILMI and microdiscectomy are safe and effective surgical procedures for treating LDH, with ILMI offering shorter hospitalization duration and reduced blood loss.
Risk Factors for Recurrent Disc Herniations
Numerous risk factors for recurrent disc herniation have been reported including smoking, diabetes, age, gender, obesity, and surgical technique for the index procedure and the configuration of the initial disc herniation. Although many of these studies, particularly those assessing age and gender, have been inconclusive in demonstrating a clear correlation with recurrent disc herniation, other studies have indicated a stronger correlation. Miwa et al. found that smokers had a herniation recurrence rate of 18.5%, which correlated with an odds ratio of 3.472 versus nonsmokers. This finding is consistent with other studies that have suggested that smoking is a risk factor for recurrent herniation. The proposed mechanisms include smoking’s detrimental effect on annulus oxygenation and nutrition, NP replication and recovery, and ligamentous healing following the primary procedure.
Another risk factor for recurrent disc herniation is diabetes. Simpson et al. reported excellent/good outcomes following the initial discectomy in 95% of nondiabetic patients but only 39% of diabetic patients. Mobbs et al. reported success rates of 86% in nondiabetic patients and 60% in diabetic patients. Although these clinical outcome differences were generally felt to be attributable to lower quality of life indicators in diabetic patients, Robinson et al. investigated the differences in the proteoglycan profile of the discs in the two groups. This study found that diabetic patients had fewer proteoglycans in their disc material, potentially increasing their susceptibility to recurrent disc prolapse.
The relationship of obesity to disc recurrence has been investigated. Meredith et al. evaluated 75 patients following one- and two-level lumbar microdiscectomy and found that patients with a BMI greater than 30 were 12 times more likely to sustain a recurrent disc herniation and 30 times more likely to require reoperation than nonobese patients. Kim et al. showed a similar association between disc recurrence and obesity following percutaneous endoscopic discectomy.
Conversely, other studies have failed to show a correlation between obesity and recurrence. In an analysis of patients enrolled in the multicenter SPORT study, Rihn et al. found that obese and nonobese patients had similar rates of recurrence (7% and 6%, respectively). Quah et al. reported lower rates of recurrence in obese (8.6%) than nonobese (10.0%) patients following single-level microdiscectomy. These and other studies indicate that obesity may not be a significant risk factor for recurrent disc herniation.
Several studies have investigated the potential association between technical aspects of the initial discectomy and recurrence. McGirt et al. found that larger annular defects and a small amount of disc removal was associated with an increased risk of reherniation whereas a more aggressive disc removal contributed to accelerated disc height loss with its associated foraminal stenosis. Although a limited discectomy procedure was found to be associated with shorter operative time, earlier return of function, and similar functional status at 6 months, the recurrence rate was 8.7% versus 3.3% rate of recurrence following a more aggressive discectomy technique.
Some studies have indicated a potential association between disc recurrence and the configuration of the initial disc herniation. Carragee et al. noted that a disc protrusion without a herniated fragment or an annular defect had the highest rate of recurrence. A metaanalysis of recurrent disc herniation reinforced this finding. A possible explanation for this finding is that a greater degree of disc removal is achieved in cases with disc extrusion or sequestration whereas less disc is removed in most cases with disc protrusion.
Evaluation of Recurrent Disc Herniation
The clinical presentation of recurrent disc herniation is generally preceded by a period of symptomatic improvement following the initial discectomy procedure. A retrospective review of 28 patients with recurrent disc herniations found a pain-free interval ranging from 7 to 168 months (mean of 60.8 months). Patients typically report radicular signs and symptoms similar or identical to their preoperative clinical state.
Pathological changes in the ventral epidural space may reflect mass effect caused by perineural scarring or a recurrent disc herniation. Scarring is most pronounced before 9 months and primarily involves the AF. The scar may surround the nerve roots and cause symptoms by neural tension, decreased axoplasmic transport, restriction of arterial blood flow, or restriction of venous return.
MRI, with and without gadolinium contrast, is the preferred imaging modality for the assessment of a recurrent disc herniation. The use of contrast material helps to differentiate normal postoperative anatomic changes from a recurrent herniation. Peridural scarring will typically enhance heterogeneously because of its vascular supply. A recurrent disc herniation usually appears as a polypoid mass with a low signal on T1- and T2-weighted sequences. It is usually contiguous with the parent disc unless sequestered. There can be a hypointense rim of the posterior longitudinal ligament and outer annular fibers that outline the herniation. This rim will enhance with contrast administration ( Fig. 8.6A, B ). The disc itself will not enhance because it is avascular.
