Low back pain may affect 60-85% of the population at least once, and 10-20% of these patients develop chronic discomfort (15,16). Degenerative disc and facet disease often accompany one another. These processes mechanically alter the spine and often reduce mobility.
The underlying pathology is often osteoarthritis at the facet joints. The cartilage lining the facets can form fissures, sites of fraying, and erosions. These changes can lead to bone hypertrophy, sclerosis, and osteophyte formation. The association of disc degeneration, loss of disc height, and slippage along the facet articulation from the degenerative process can create a dynamic instability of the ligament support, which can result in forward motion of one vertebra on the other with or without a pars defect. The forces that destabilize the spine work not only in a transverse fashion but also in an axial fashion. The facet joint carries up to one third of the static compression load of the lumbar motion dynamically and as much as one third of the axial load depending on the position of the spine, as reported by Yang and King (17). Facet joint changes are more often noted at the L4-5 level and are commonly found in younger patients with congenital anomalies of fusion in the lumbosacral region.
History The pain of the back created by facet disease can be challenging to characterize. The pain can be unilateral or bilateral, cervical or lumbar. The discomfort may be a deep dull ache that is difficult to localize. The pain is associated with twisting and bending and may be aggravated by sitting and relieved with walking. The discomfort may be worse in the mornings or after prolonged rest and inactivity.
Other patients may present with a slowly developing back pain that appears to worsen with activity and to be relieved with rest. The back pain is often accompanied by leg pain, which may be radicular. Patients with facet disease may develop neurogenic claudication in the later stages of the disease process. The spinal canal is narrowed and the thecal sac constricted from the combination of facet hypertrophy with osteophyte formation, bulging of the ligamentum flavum, disc degeneration, and herniation. Patients with neurogenic claudication complain of bilateral thigh and leg tiredness, aches, and fatigue. They also report that forward flexion of the spine, as with leaning on a counter, relieves the symptoms. In the setting of long-standing disease, patients may discover a slow onset and chronic loss of bladder control. Associated conditions, such as prostatism in men and bladder suspension in women, should be ruled out.
Physical Examination Impairment caused by low back pain can be evaluated by a physical assessment. Evaluation of the patient's response to lumbar flexion, trunk flexion, extension, lateral flexion, straight leg raise, tenderness to palpation, and a sit-up procedure can help characterize and measure the degree of impairment. The patient's gait may demonstrate a forward stoop. The forward flexion in the stoop relieves discomfort by increasing the AP diameter of the central canal.
The range of motion test is commonly normal. Typically, motor strength is intact and rarely is there weakness. Patients may have vague paralumbar tenderness when palpated over the facet joints. In the acute setting, warmth and muscle spasm are present. At times there are no neurological findings. Although the patients have pain in the buttocks, hips, and thighs, the discomfort does not extend below the knees. The discomfort is aggravated with extension of the back and hyperextension of the spine. From the prone position the patient is asked to arch the back and extend the spine, which may re-create the pain in the lumbar, thoracic, and cervical regions. Passive range of motion twisting, lateral bending, and rotational movements from the sitting position can exacerbate the symptoms. The recumbent position can sometimes provide pain relief. The sensation and response to vibration are intact. The deep tendon reflexes will generally be normal to diminished.
Diagnostic Imaging Routine radiographs to evaluate a patient with lumbar pain include AP and lateral radiographs with the patient standing. Radiographs of the lumbar spine in the oblique projection and in flexion and extension as well as an AP radiograph of the pelvis would form a complete protocol. If a spondylolisthesis is discovered it should be graded 1-4 based on the percent of slippage, that is, 25%, 50%, 75%, or 100% (18).
In cases of mechanical back pain related to bony disease, the hypertrophic bony changes originating in the facet joints of the posterior elements are better evaluated with CT. The bone overgrowth and proliferation commonly narrow the neural foramen. When the facet joints narrow, occasionally a vacuum phenomenon or intraarticular gas can be seen in the narrowed facets.
MRI can show signal in the synovial joint, and the earliest degenerative changes may be detected. Synovial cysts and signs of inflammatory disease can also be detected. The hypertrophic bone changes of the facets are not as readily seen by MRI because bones generate little signal. Associated disc degeneration and herniation are readily seen by MRI. Sagittal and axial T1 and T2 images demonstrate loss of the epidural fat as degenerative facets compromise the thecal sac and neural foramen.
The radionuclide bone scan with single photon emission computed tomographic (SPECT) imaging displays abnormal accumulation of activity in the facet joints of the spine. SPECT imaging has a high sensitivity for osteo-arthritis in the facet joints as the tomographic technique removes the activity from overlying tissue and bone and the facets become pronounced. The presence and sensitivity of facet disease are further enhanced by diphos-phonate radiotracer compounds, which have a high affinity for reactive bone.
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