Lumbar degenerative disc disease

Introduction

Low back pain is a very common complaint, affecting up to 80% of individuals at some point throughout their lifetime.^1,2 In whole, low back pain is a common primary care complaint and may result in significant disability, lost work time, and even depression. While a significant portion of the population will develop low back pain, only a small percentage (approximately 1%) will require long-term treatment.³

Low back pain may be caused by any number of conditions, including:

• Facet joint arthrosis
• Degenerative or herniated discs
• Osseous injuries
• Muscular strains

It is essential, though often difficult, to accurately diagnose the causal origin of low back pain to guide treatment modalities. In this article, we examine lumbar degenerative disc disease (lumbar DDD) as a cause of low back pain.

Anatomy

The intervertebral disc is composed primarily of two structures — the annulus fibrosis and the nucleus pulposus, which is surrounded by the annulus fibrosis. The nucleus pulposus has a very high water content and resists axial forces. The annulus fibrosus helps to resist shear forces, and is composed of much more dense tissue.

Pathogenesis

The pathogenesis of lumbar DDD is incompletely understood, but is thought to start with microtrauma that causes fissuring in the annulus fibrosus. Patients will have characteristic changes in magnetic resonance imaging (MRI, discussed later) consistent with decreasing water content in the intervertebral disc. However, this does not always correlate with patient symptoms. Not all patients who experience chronic low back pain have evidence of degeneration on MRI, and not all patients with MRI evidence of degeneration have clinical manifestations.

Clinical Presentation

Lumbar DDD, or discogenic back pain, is part of the constellation of lumbar spondylosis. The diagnosis generally refers to mid-axial low back pain without radicular symptoms in patients with an arthritic-appearing disc on imaging.

The clinical presentation may vary widely, from mild, mid-axial pain to severe debilitating pain that may radiate into the sacroiliac or buttocks region. Pain may or may not be reproduced with direct palpation. Straight-leg raise or other provocative maneuvers are often negative.

Given the unreliable examination, it is imperative to elicit an accurate history, looking for “red flags” (fevers, night sweats, recent weight loss, abdominal discomfort), as many non-spinous abnormalities may result in low back pain — aortic aneurysm, pancreatitis, or intra-abdominal tumors, for example. Any concerning reported symptoms should prompt further workup to rule out other potential pain generators.

As a result of inconsistent physical exam findings and the multiple potential etiologies of low back pain, lumbar DDD should remain a diagnosis of exclusion.

Imaging and Diagnostic Studies

Radiographic evaluation consists initially of upright anteroposterior and lateral lumbar spine plain films. These may be helpful in the diagnosis of spondylosis, disc space narrowing, end plate sclerosis, osteophyte formation, antero- or retro-listhesis, or other osseous abnormalities. In the absence of history and physical exam signs that would indicate dynamic instability (ie, radicular pain with extension), the routine use of flexion and extension radiographs is likely unnecessary.⁴

Magnetic resonance imaging is the next diagnostic modality of choice, and it is often pivotal in obtaining an accurate diagnosis. Discs should be evaluated for signal intensity and height. Changes in these characteristics are thought to be due to microtears in the annulus, leading to progressive loss of fluid content in the affected disc. Changes are graded on a scale of 1-5, based on Pfirrmann et al (Table 1).⁵

Table 1. Pfirrmann MRI Appearance of Lumbar Disc Degeneration

The vertebral end plates and adjacent vertebral body bone marrow may demonstrate changes in signal intensity on MRI as disc degeneration progresses, as described by Modic et al.⁶ These changes may represent the early stages of disc degeneration.^6,7

• Type I changes were low-signal intensity on T1, high-signal intensity on T2, and associated with areas of degeneration, increased amounts of woven bone and vascularized granulation tissue.
• Type II MRI changes consisted of increased signal on both T1- and T2-weighted images, which was associated with fat replacement of hematopoietic elements and evidence of chronic, repetitive trauma.
• Type III Modic changes are signified by decreased signal on T1 and T2, and represent advanced disc degeneration and end plate sclerosis.

While imaging studies are essential for diagnosis in many cases of low back pain, care should be taken when critically comparing imaging studies with history and physical exam in the lumber spine, as many asymptomatic patients will often have findings consistent with significant lumbar DDD on plain radiographs and MRI.^8-10 Additionally, even Modic changes have been shown recently to be unreliable in predicting which patients have back pain due to disc degeneration.^11,12

Discography is a diagnostic modality that combines imaging and direct stimulation of the disc to determine its potential as a pain generator. A positive test contains the following elements:

• Low velocity dye injection (which produces pain at the degenerated level)
• Evidence of dye extravasation signifying annulus injury
• No significant pain response when dye is injected into an adjacent level

Logically, such results would indicate that patients may likely improve from a fusion surgery. Although historically deemed the diagnostic modality of choice, several studies have questioned the reliability of discography in diagnosis and predicting treatment outcomes; it may even result in deterioration of the disc levels studied.^13-15 While recent studies have questioned its diagnostic utility, discography still remains a potentially useful tool in the properly applied setting.^13,16-21

Treatment

Treatment for lumbar DDD centers on non-operative therapy, as the percentage of individuals with complaints of low back pain who improve within 3 months is 90%.¹ Several studies have demonstrated improvement in symptoms of low back pain with conservative treatment, including non-steroidal anti-inflammatory medications, physical therapy, and lower back pain education.^22-25 Although pain management can be a clinically difficult problem, providers are cautioned against the use of narcotics when treating lumbar DDD, as NSAIDs have been found to be successful in mitigating acute pain attacks in this condition based on a recent Cochrane review.²⁶ Muscle relaxants have also shown some utility, although they carry a more significant side effect profile and should be used judiciously.²⁷

Given the success of non-operative intervention in management lumbar DDD, these modalities ought to be utilized fully prior to any invasive procedures. Intersegmental arthrodesis has been the historical treatment of choice for patients who have failed non-operative therapy; however, the data demonstrate inconsistent results with regard to pain relief, return to work, and patient satisfaction. Most experienced surgeons agree that one should exhaust all non-operative modalities prior to surgical management.

Injections

Epidural steroid injections have been used to treat low back in patients with degenerative discs; however, the current literature fails to support their use in this particular instance. Epidural steroid injections are useful in the management of spinal stenosis or herniated nucleus pulposus. Facet injections and medial branch neurotomies are designed to treat facet joint pain generators, and not specifically discogenic back pain. One recent study demonstrated short-term benefits associated with intradiscal steroid injections; however this is not widely practiced.²⁸

Arthrodesis

Lumbar fusion has been the “gold standard” for surgical management of discogenic low back pain. For appropriately selected symptomatic patients, arthrodesis of the affected level may be a reliable method of pain relief, although it still remains a controversial treatment modality.

Historically, outcomes from fusion have been inconsistent and related to workman’s compensation, age, smoking, and psychosocial comorbidities. Turner et al evaluated 25 years of data retrospectively and found that the average patient satisfaction rate was 68% with a very wide range, from 16% to 95%.²⁹ The authors concluded that surgical intervention was not reliably more effective than non-surgical management. The wide range of outcomes from the study by Turner et al was likely due primarily to improper patient selection for surgery; however, the study did cast doubt on the effectiveness of surgical intervention for discogenic back pain.

Arthrodesis options include anterior lumbar interbody fusion (ALIF), transforaminal or posterior lumbar interbody fusions (TLIF/PLIF), or circumferential fusion. In a 2009 study, Burkus et al examined the results of 130 ALIF procedures performed for lumbar DDD. They demonstrated fusion in greater than 98% of patients at 6 years, with sustained pain relief and a 10% reoperation rate. There were no instances of vessel injury or retrograde ejaculation reported.³⁰ However, the complications of an anterior, retroperitoneal approach are well documented, with one study showing a 38% complication rate, including sympathetic dysfunction, sexual dysfunction, prolonged ileus, vessel injury, deep venous thrombosis, wound dehiscience and bowel injury.³¹ The advantages of an anterior approach are minimal muscle dissection and greater access to interbody space to allow for complete disc removal and creation of a large fusion surface.

Posterior fusions have yielded similar results without the complication profile of anterior approaches. A recent study compared TLIF (an all-posterior 360-degree fusion) to a combined anterior and posterior surgery (AP), and concluded that the outcomes were similar in both groups, but that the AP group had twice the complication rate and significantly increased surgical time and blood loss compared to the TLIF group.³²

A systematic review of prospective randomized controlled trials regarding surgical management for symptomatic lumbar DDD highlighted the need for accurate patient selection. Carreon et al reviewed 25 studies and determined a significant improvement in the Oswestry Disability Index (ODI) for patients with degenerative disc disease following spinal fusion.³³

While spinal fusion has been the historical “gold standard” for ultimate treatment of symptomatic degenerative disc disease, recent literature demonstrates evidence of adjacent segment degeneration following fusion. Ghiselli et al in 2004 determined that the rate of further surgical intervention (additional level decompression or fusion) due to adjacent segment degeneration was 16.5% at 5 years and 36.1% at 10 years.³⁴ This study, among others, prompted development of a “motion-sparing” treatment modality — the lumbar total disc arthroplasty.

Total Disc Replacement

Total disc replacement (TDR) is currently approved as an alternative to fusion for patients with intractable axial back pain due to degenerative disc disease. The list of contraindications is extensive, including any evidence of segment instability, global stenosis, facet arthrosis, scoliosis, osteoporosis, and obesity. The goal of the surgery is to remove the determined pain generator while allowing near physiologic range of motion at the treated segment in an effort to decrease adjacent segment degeneration. In a study of 106 patients treated with lumbar total disc arthroplasty, David et al reported an 82% patient satisfaction rate with a low rate of reoperation (2.8%) for adjacent level disease following lumbar disc arthroplasty at 10 years.³⁵

In a prospective randomized controlled trial, Guyer et al compared ALIF to TDR for patients with discogenic back pain and found that both groups improved significantly with regard to pain relief and disability and had similar complication profiles.³⁶ These results have been supported by other studies.^37,38 These studies conclude that TDR is a reasonable alternative to fusion for lumbar DDD in patients without TDR contraindications.

A recent study by Gornet et al demonstrated superiority of TDR compared to fusion with regard to patient satisfaction, back pain, and SF-36 and ODI scores. The TDR group did have longer surgical times and increased blood loss, although their hospital stays were similar and the TDR group had an earlier return to work time.³⁹ Another study demonstrated significantly decreased hospitalization time and decreased reoperation rate.⁴⁰ Multiple other studies have validated the use of TDR in patients with lumbar DDD, and Bertagnoli et al showed that TDR may be a useful treatment modality for adjacent segment disease, citing significant improvement in patient pain, ODI scores, and an 85% patient satisfaction rate when performed adjacent to a prior lumbar fusion at 2-year follow-up.^41-43

Complications associated with TDR include facet degeneration, implant migration, and subsidence.⁴⁴ Given these complications, however, a prospective, randomized trial demonstrated that reoperation rates for TDR were slightly lower compared to those for lumbar fusion (8.8% vs. 10.1%, respectively) at 2 years.⁴⁵

TDR is currently considered by many to be a viable alternative to fusion for DDD in the lumbar spine, with the added benefits of motion preservation and theoretical decrease in adjacent segment degeneration.

Conclusion

Low back pain associated with lumbar DDD can be a very difficult problem in terms of patient dissatisfaction and provider management. Given that a vast majority of patients will improve without surgical intervention, non-operative therapy remains the mainstay of treatment.

Providers are cautioned to rule out all other potential causes of back pain prior to proceeding with any surgical management, as many other processes may refer pain to the lower back. However, for appropriately selected patients with intractable axial back pain due to lumbar DDD, there may be a significant benefit from surgical intervention in the form of spinal fusion or disc arthroplasty, both of which have demonstrated significant relief of pain and disability throughout the medical literature. While initial data appear promising, more long-term studies are necessary to determine if TDR produces improved outcomes compared to fusion.

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