 The Investigators have designed this exploratory study in patients suffering from zygapophysial joint mediated pain to investigate if a correlation exists between inter-individual genetic variability genotype with treatment response phenotype. More specifically, the investigators aim to identify any form of correlation between a specific SNP of the BDNF gene Val66Met and the effectiveness andor duration of radiofrequency facet joint neurotomy. The study population is patients suffering from chronic low back pain who have been scheduled for radiofrequency neurotomy following the diagnosis of facet joint mediated pain using medial branch block test. The investigators will evaluate if a common variant of BDNF gene Val66Met can be directly correlated to a significant degree of pain relief following RF treatment, and whether the result of such a procedure can be predicted from a specific genetic profile. 