Can diagnostic injections predict the outcome in foot and ankle arthrodesis?

BACKGROUND: Intra-articular anesthetic drug injections are claimed to confirm the localization of the pain in order to treat the pain. The aim of the present study was to evaluate whether a positive effect of injection could be indicative for a successful outcome of future arthrodesis. METHODS: 74 Patients underwent fluoroscopically guided and contrast confirmed anesthetic joint injections for diagnostic reasons. Before and after injection, pain was measured by use of the Visual Analogue Scale (VAS) in rest and after exercise. Pain reduction was expressed as delta VAS (dVAS). Also, the Foot Function Index (FFI) was obtained. Based on the effect of the diagnostic injection and various clinical factors, patients were advised a conservative treatment (conservative group, n = 34) or an arthrodesis of the affected joint (operative group, n = 40). After a median follow-up period of 3.6 years (range 2.1 to 4.3 years) patients were again invited to complete the FFI and VAS in rest and after exercise. For data-analysis purposes the patients were assigned to four different groups, based on the result of injection and the occurrence of surgery. Wilcoxon signed rank tests and Mann Whitney U tests were used for statistical analysis. RESULTS: Based on the analysis of the four groups we found that surgery, irrespective of the presence of pain reduction after injection, was related to improvement of VAS and FFI. Patients with conservative treatment always showed worse VAS and FFI scores, even when previous injections showed an improvement of VAS. CONCLUSIONS: Fluoroscopically-guided anesthetic injections of the supposed painful foot-ankle joint seem not to be indicative for a successful outcome of an arthrodesis of the affected joint. However, the sole occurrence of surgery shows a significant difference in VAS and FFI scores, where conservative treatment does not. The local hospital review board granted permission for this study. Ethical approval was not required for this study.