Are Diagnostic Lumbar Facet Injections Influenced by Pain of Muscular Origin?

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Abstract
Introduction: Nonradicular low back pain can be a difficult entity to accurately diagnose and treat. Facet joints, muscle, ligaments, and fascia have all been reported to be etiologies of acute and chronic low back pain. However, the facet joint as a source of low back pain is controversial. The diagnosis of facet joint pain is made by diagnostic facet joint or median nerve branch injections with a local anesthetic. The purpose of this study was to determine if the results of diagnostic facet joint injections are influenced by the technique used to perform these injections. Methods: Seventy-five male patients aged 45 years or younger and 18 years or older who were injured while performing heavy work with nonradicular low back pain were included in this study. Diagnostic injection therapy was performed following Institutional Review Board approval and the patient's informed consent. Patients were assigned to one of five groups to receive diagnostic injections in a double-blinded fashion as follows: Group I: facet joint injection with continuous lidocaine administration from the skin to the facet joint as the needle was advanced; Group II: facet joint injection with saline administration from the skin to the facet joint as the needle was advanced; Group III: median nerve branch injection with a lidocaine advancing needle technique; Group IV: median nerve branch injection with saline advancing needle technique; and Group V: injection of the paraspinous muscles with local anesthetic and steroid following noted areas of pain diagnosed with saline injection and radiopaque contrast. After one week, the patients in Groups I to IV who had no pain relief with facet joint or median nerve block injections subsequently received paraspinous muscle injections, while the patients in Group V who had no long-term relief with muscle injections were given facet joint injections. The appropriate parametric and nonparametric tests were performed with statistical significance defined as P ≤ 0.05. Results: There were no differences among the groups demographically. The incidence of pain relief was significantly higher in subjects who had a continuous injection of local anesthetic into their musculature than in those individuals who received continuous saline followed by an injection of local anesthetic into their facet joint or median nerve branch. Discussion: The results of this study demonstrated that local anesthetic injections are useful for the diagnosis of nonradicular low back pain but may yield false positive results with respect to lumbar facet pain depending upon the technique utilized.