A screening block followed by a confrrmatory block using different anesthetic agent is a common method used to identify the zygapophysial joint (ZJ) as a tissue origin of LBP. While previous studies have identified potentially valuable clinical tests, identification of patients unlikely to respond to the initial screeuing block is desirable.
To estimate the predictive power of specific clinical findings in relation to screening ZJ blocks.
A prospective blioded study carried was out in a private radiology clinic specializing in the diagnosis of spinal pain.
Chronic LBP patients received screening ZJ blocks (N=151) with 120 patients included in the analysis after exclusions.
Pre and post procedure pain intensity was measured using a standardized VAS. A 95% reduction in pain following ZJ block was defmed as a positive response.
Patients completed pain drawings, psychosocial distress and disability questionnaires. Thereafter they received a clinical examination and screening lumbar zygapophysial blocks. History, demographic and clinical variables were evaluated in logistic regression models with sensitivity, specificity and likelihood ratios being calculated for potentially useful variables.
A positive screeulng ZJ block was reported by 10.8% of patients. Sensivity of the extension rotation test was 100% and specificity 22%. No positive responders reported centralization or peripheralization of pain. The best predictors of a positive response to ZJ block were: age over 55 (odds ratio 3.55, p=0.06); report that walking (odds ratio 4.79, p=0.02) and sitting (odds ratio 4.27, p=0.04) were the best activities for pain.
A negative extension rotation test, centralization or peripheralization can rule out ZJ mediated pain. Age over 55 and report of walking and sitting being the best activities for pain, are associated with a positive response to screening ZJ blocks.