Goal of the Study?
The objective of this study 1, is to determine the prevalence of “pure” lumbar Z joint pain.
Why are they doing this study?
The prevalence of lumbar Zygapophysial joint (Z joint) is disputed, with rates ranging from 5% to 45%. The reason for this disparity lies in the use of different criteria for diagnosis. The criteria are focused on relief of pain after a diagnostic block, an injection of numbing medication into 1 or more small joints on each side of the vertebrae. However, these criteria can range from 50% to 80% to complete pain relief after a diagnostic block. Additionally, some diagnostic criteria focus on relief from pain after a single diagnostic block, with no controlled blocks. However, the researchers argue that for diagnostic blocks to be valid, pain must be abolished whenever an active agent is administered, and the use of repeat blocks provides validity.
The authors contend that no research has been able to determine the prevalence of “pure” lumbar Z joint pain, defined as complete relief of pain following a placebo-controlled diagnostic block.
What was done?
All 206 patients for this study came from a private practice where they were referred for back pain. To be eligible, they had to have back pain longer than 3 months, with symptoms compatible with a potential diagnosis of lumbar Z joint pain. Patients with imaging that pointed to tumours or infections were excluded from this study, as were patients who were pregnant or had pain in the lower limbs.
The researchers used two protocols for this study. The first protocol was a placebo-controlled local anesthetic comparative blocks. For this, each patient received a local anesthetic on two occasions and normal saline on one occasion. For the second protocol, patients could receive the same or a different local anesthetic on two or three occasions and normal saline on one or no occasion. Using saline as a placebo showed whether patients could tell the difference between an active control from a placebo.
Patients were considered to have Z joint pain if they had complete relief of pain three times when a local anesthetic was used, if they had complete relief of pain two times when the anesthetic was used, and if they had no relief, saline (the placebo) was used.
What did they find?
The majority of patients did not report any pain relief from the initial block and therefore did not satisfy the criteria for lumbar Z joint pain. Only patients who had complete relief of pain from their initial block were eligible to continue.
Of eligible patients, the researchers found that 45% of patients in group 1 and 30% in group 2 did not get relief from the second block. Moreover, 20% of patients in group 1 and 3% in group 3 had no relief from the second block but were completely relieved by the placebo. Results for the two groups combined showed a prevalence rate of “pure” lumbar Z joint pain of 15%. This is much lower compared to when a diagnostic criterion is less stringent. Moreover, they did not find any statistically significant differences between the two groups for gender and age.
Why do these findings matter?
Determining the appropriate diagnostic criteria for lumbar facet pain has important implications for patients who need to have the right diagnosis and treatment for their pain.