Degenerative Disease

Introduction

Acute and chronic low back pain is a ubiquitous complaint encountered by primary care physicians throughout the United States, accounting for the second most common symptomatic reason for office visits. Low back pain is the leading cause of disability for patients younger than age 45, resulting in lost time from work and decreased work productivity, with increasing cost expenditures for evaluation and treatment of back pain estimated at $90 billion annually ($4695 per year in 1997 vs. $6096 in 2005); it is thus considered a major public health issue in the United States.

The most common reason why patients undergo imaging of the spine is pain. Degenerative/acquired and congenital spinal stenosis, neoplasm, infection, trauma, inflammatory or arthritic processes are all known causes of back pain. However, a majority of patients presenting with neurogenic intermittent claudication and radiculopathy is the result of acquired “degenerative” spondylotic changes as the cause of central canal, subarticular recess, and/or neuroforaminal compromise. Acquired degenerative disease is due to a combination of bone, ligament, joint, and disk disease, most commonly affecting the lumbar spine, followed by the cervical spine. Thoracic disk disease is now more commonly recognized with the increased use of magnetic resonance imaging (MRI).

Imaging Guidelines, Techniques, and Methods

Advanced imaging has led to a more accurate understanding of radiographic changes throughout the spine that are now known to occur as part of the normal aging process. However, imaging does allow for accurate assessment of mechanical causes of nerve root compression, offering objective evidence in support of a clinical diagnosis of back pain or radicular symptoms. Conversely there is a high prevalence of abnormal computed tomography (CT) and MRI findings in asymptomatic patients. Degenerative changes involving the intervertebral disks or facet joints have not been proven to correlate with back pain, because many patients without back pain demonstrate zygapophyseal joint osteoarthrosis, disk desiccation, reduced disk height, annular tears, and disk protrusions. Thus degenerative changes may be coincidental, given the poor association between low back pain and anatomic findings, and when found at imaging are not correlative of a patient's pain or predictive for the development of back pain.

The use of advanced spine imaging has continued to rise rapidly, with MRI often being performed on patients not having received a trial of conservative therapy as currently recommended. The natural history of disk herniation is spontaneous regression, with extrusions and sequestrations demonstrating a higher trend toward resolution. Although multiple sources have confirmed that uncomplicated acute low back pain and/or radiculopathy is a benign self-limited condition that does not warrant imaging, many patients continue to undergo radiographic or advanced imaging evaluations without a clear indication. Improvement in pain and functional status usually occurs in most patients presenting with acute back pain (with or without radiculopathy) within 4 weeks regardless of treatment. It has been shown that routine imaging does not improve clinical outcomes, may expose patients to unnecessary radiation and invasive procedures, and contributes to rising healthcare costs. Owing to the ever-increasing trend in spine imaging and the associated expenditures, multiple medical professional organizations have issued recommendations and practice guidelines to address the overutilization of spine imaging.

Updated in 2015, the American College of Radiology (ACR) published appropriateness criteria for diagnostic imaging in patients with low back pain presenting with various scenarios, which were in parallel with previous guidelines from the American College of Physicians and the American Pain Society. In summary, the ACR appropriateness criteria recommend lumbar radiography as the initial evaluation for low back pain in patients with recent trauma, osteoporosis, on chronic steroids, patients suspected of vertebral compression fracture, and in the evaluation of young patients for ankylosing spondylitis. However, low back pain complicated by “red flags” may justify the use of CT or MRI. In the setting of major trauma, patients with neurologic compromise, history of malignancy, and patients at risk for vertebral infection for which clinical decision making may be directly influenced, advanced imaging should be performed. Furthermore, for low back pain complicated by radicular symptoms lasting longer than 6 weeks following a trial of conservative therapy, MRI should be performed, especially in patients who may be candidates for surgical intervention or percutaneous epidural steroid injection. As can be expected, the challenge for the referring physician is to distinguish this smaller group of patients who may require further workup and advanced imaging because of suspicion of a more serious underlying process.

Multiple imaging modalities have been used in the evaluation of degenerative disk disease, including radiography, diskography, CT, myelography with postmyelographic CT, MRI, and scintigraphy, which contributes to the dilemma of their application.

Lumbar Spine