A study 1 of sensory hypersensitivity in patients suffering from chronic whiplash associated disorder 6 months or more after being involved in a motor vehicle collision (MVC) found that the hypersensitivity was reduced, and pain thresholds were increased after receiving a medial branch block (MBB) procedure of the cervical spine. The results of the study indicate the cervical zygapophyseal joints most likely contribute to sensory hypersensitivity caused by peripheral and centrally mediated pain.
What’s at Stake?
A common problem of people who have been involved in MVC’s is chronic whiplash associated disorder (WAD). According to research, between 32-56 percent of those involved in MVC’s may continue to suffer from related disability or pain 6 months or longer after their accident. Research has implicated the cervical zygapophyseal joint as a possible source of chronic hypersensitivity in 54-60 percent of subjects with WAD—evidence that is supported across multiple biomechanical and neurophysiological studies. It is thought that tissues that had been seemingly unaffected by the MVC experience sensory hypersensitivity when the body’s pain processing mechanisms are altered in the spinal cord. This sensory hypersensitivity and central nervous system hyperexcitability decrease the pain thresholds in the body, creating an exaggerated response for thermal, electrical, or mechanical stimuli for WAD patients. The prognosis for WAD patients suffering from sensory hypersensitivity is poor, and better understanding of the phenomenon could improve long-term treatment outcomes.
The pretest-posttest exploratory study involved 18 volunteers (15 females, 3 males) with an average age of 45 years and who had experienced WAD for 6 months or longer, with numerous neck complaints, body tenderness, and decreased range of motion. A control group of 18 healthy patients (15 females, 3 males) with an average age of 45 years also participated in the study. A group of chronic WAD patients with pain reported for 6 months or longer and who had a minimum of 80 percent decrease in neck pain intensity following an intra-articular zygapophyseal joint block procedure also took part in this study. Exclusionary criteria included pregnancy, previous history of headaches or neck pain requiring treatment, central or peripheral neurological problems, coronary artery or peripheral vascular disease.
Researchers rated the subjects’ pain intensity levels on a scale of 1-10 before and after receiving MBB procedures. Quantitative sensory testing (QST) based upon pressure pain thresholds (PPT’s) and cold pain thresholds (CPT’s) were conducted on the control and WAD groups. All measures were recorded, including patient demographic variables and their current MVC litigation status.
Cold Pain Threshold Testing
A 30mm x 30mm thermode set to 32 degrees Celsius placed over the anaesthetized articular pillars of the cervical zygapophyseal joints measured cold pain thresholds in the test subjects as the temperature was decreased at the rate of 1 degree Celsius per second. Patients used a self-controlled switch to indicate when the sensation of cold turned to pain as each bilateral site was tested. (The minimum temperature was 1 degree Celsius.) The average values were gathered for analysis.
Pressure Pain Threshold Testing
The articular pillars of the cervical zygapophyseal joints, peripheral nerve trunk of the median nerve, and the tibialis anterior were measured in the PPT tests, with the subjects using a self-controlled switch to indicate when the sensation of pressure turned to one of pain. The tests were performed three times bilaterally on each site, with a pause of 10 seconds between each test. The average values were recorded and later statistically analyzed.
Diagnostic Cervical Zygapophyseal Joint Blockade
The patient group with chronic WAD underwent two diagnostic zygapophyseal joint block procedures—one, prior to the study, where a spinal needle was inserted with fluoroscopic guidance into the joint while the patient was in the prone position. An injection containing a local anesthetic and a corticosteroid was made into the affected zygapophyseal joint. If these patients experienced a relief of pain intensity of at least 80 percent but their pain later returned, they received the second MBB injection. In this study, none of the patients were excluded from the second MBB, as each of them had experienced at least an 80 percent reduction of pain from the first procedure, with the return of pain post-procedure.
The WAD patients demonstrated clinically significant changes in their sensory hyperactivity measurements after the blockade of the cervical zygapophyseal joint. These changes included a decrease in CPT’s and increase of PPT’s in the cervical spine and distal sites. This finding is unique in the study of chronic WAD patients and suggests that minimizing the source of pain—in this case, the zygapophyseal joint—may help modulate sensory hypersensitivity in chronic WAD patients, at least in the short-term. The study authors urge larger trials with long-term follow-ups of patients to gather more information and improve the treatment outcomes of patients with WAD.