Diagnosing Low Back Pain

Given the large number of people who have had or have back pain in their lifetime, it is surprising that only 15 per cent of the time back pain has been specifically diagnosed in the past. This means that the great majority of back pain was termed non-specific. This also means that treatments were not targeted to specific parts of the spine.

Facet joints, discs, ligaments, nerve roots, and muscles can all be a source of back pain. Some can be eliminated as a source of pain given a patient's symptoms, physical examination, or imaging such as Xray or MRI.

More recently, doctors, with the help of injections that numb certain parts of the spine, can make a specific or positive diagnosis in up to 85 per cent of patients.

Studies have shown that facet joints, the small joints in the spine, may be the source of neck, midback (thoracic), and low back pain 25 to 40 per cent of the time.

Diagnosing the facet joints as the source of pain requires performing a sympathetic nerve block using a numbing agent such as lidocaine. This is done using an xray technique called fluoroscopy to insure the medication goes where it is intended. The lidocaine is used to block the nerve to the targeted facet joint(s). The authors chose to perform blocks at a minimum of two levels to block a single joint. Target joints were identified by the pain pattern, local or paramedian tenderness over the area of the facet joint, and reproduction of pain with deep pressure.

The authors of this study considered a positive response when at least an 80 per cent reduction in pain with ability to perform previously painful movements was achieved. A verbal numeric pain rating scale was used. Pain relief had to last for two hours when lidocaine was used. Because of the known high incidence of false positive results with just one set of injections, the authors repeated the injection with a longer acting numbing agent, bupivacaine. If this decreases pain by 80 per cent for three hours or longer and allows improvement in function, then a positive response was diagnosed. Any other response was considered a negative outcome.

The authors found that 42 to 45 per cent of the time just one set of facet nerve blocks was not accurate in making a positive diagnosis in the neck, the thoracic or lumbar spine. The authors felt that given the high false positive results with single blocks, a second set of blocks should be done after an initial positive response to ensure proper diagnosis and treatment.

Rajeev Manchukonda, BDS et. al. Facet Joint Pain in Chronic Spinal Pain: An Evaluation of Prevalence and False-positive Rate of Diagnostic Blocks. Journal of Spinal Disorders and Techniques. October 2007. Volume 20. Number 7. Pp. 539-545.

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