Degenerative disc disease (DDD) is typically used to describe the clinical scenario of low back pain and wear-and-tear (arthritic) changes of the intervertebral disc. To classify this condition as a “disease” is probably inappropriate, because nearly every person will develop degenerative changes of the intervertebral disc during their lifetime, many beginning in the third decade of life. The disc is a cartilaginous symphysis joint that bears nearly 90% of the load of the spine, while the facet joints bear approximately 10%. The discs of the spine are joints, and just like all joints in the human body, the discs undergo arthritic changes during the course of life. Despite being so prevalent, the vast majority of people never develop significant chronic back pain as a result of this condition. The concept of a discogenic injury and degeneration causing back pain was first reported by Goldthwait in 1911, followed by a larger study in 1925 by Danforth and Wilson. Kirkaldy-Willis described the diagnosis as a cascade of degeneration with four phases. There are some patients who develop severe back pain solely due to degenerative disc disease, yet the majority of patients with severe symptoms also have some other spinal disorder such as herniated disc, spinal stenosis, fracture, or spondylolisthesis.
There are a number of specific causes of degenerative disc disease, ranging from an initial injury to the annulus (outer ring of the disc), facet joint injury, fractures, infections or rheumatologic etiologies (causes). Many of these conditions affect the biomechanics and/or biologic characteristics and ultimately lead to a derangement of the normal cartilage and its ability to function. However, the precise cause of DDD is unknown in most cases, yet is assumed to be the result of normal aging in most of these cases.
As previously discussed, the majority of people with degenerative disc disease do not have significant debilitating symptoms. The patients that do have pain generally have a predominance of low back in the region of the disc disease. Unless there is another associated condition, patients generally do not leg pain symptoms or neurologic abnormalities such as weakness, numbness, or bowel/bladder dysfunction.
The physical findings for degenerative disc disease are nonspecific. Patients may have an antalgic gait and significant lumbar tenderness if the pain is severe. Often, the lumbar range-of-motion is decreased, but the neurologic examination is normal. Special tests such as the straight leg raise test and Leseague’s test are usually negative.
X-rays may show that a disc height is diminished, thus confirming the diagnosis of DDD. An MRI is generally recommended so as to identify if there is an associated disc herniation or spinal stenosis, which would impact the treatment regimen. An MRI will also clarify the severity of degenerative disc disease.
There are no laboratory tests used to diagnose a herniated disc. Occasionally, specific tests are ordered to rule out infection or other medical/rheumatologic conditions.
A discogram is a test that is performed to help identify which degenerated disc, if any, is causing a patient’s back pain. A doctor performs this procedure by injecting radiopaque dye, under pressure, into the discs of the lumbar spine. The procedure is performed using fluoroscopy, a special x-ray machine that allows x-ray images to be viewed instantly on a television monitor.
The diagnosis of degenerative disc disease is ultimately confirmed if moderate or severe disc height loss is observed on a lumbar x-ray. Otherwise, an MRI test would be required to identify this condition if there is only mild DDD. The doctor must then evaluate the location and quality of the back pain to determine if the degenerated disc is actually generating the patient’s pain.
The treatment for degenerative disc disease is primarily conservative. The majority of patients with significant pain generally improve with time, as well as non-operative treatments such as oral medications, physical therapy, and other modalities. Epidural steroid injections and facet joint injections are usually not efficacious unless there are other associated spinal conditions such as spinal stenosis, herniated disc, etc.
Patients that fail all conservative treatments and still have disabling degenerative disc disease pain after 6-12 months are considered candidates for surgery. It is usually advised and recommended that a patient undergo discography prior to surgery to identify the specific disc that is generating a patient’s pain. However, some authors argue that discography is not a very reliable or valid test, and is not always necessary or useful. The surgery for isolated degenerative disc disease is spinal fusion or artificial disc replacement (disc arthroplasty). A disc excision, decompression, and/or laminectomy may also be required if a patient has concomitant spinal stenosis or disc herniation.
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