Randomised controlled trial evaluating the short-term analgesic effect of topical diclofenac on chronic Achilles tendon pain: a pilot study

OBJECTIVES To determine if a topically applied non-steroidal anti-inflammatory drug (diclofenac) can provide short-term pain relief for chronic Achilles tendinopathy (CAT), in order to inform the development of a new rehabilitation protocol. DESIGN AND SETTING Pilot double-blind, cross-over randomised controlled trial providing participants with tertiary care. The study was conducted at a single research centre in Vancouver, BC. PARTICIPANTS Sixteen adults with unilateral CAT and three adults with bilateral CAT participated. INTERVENTIONS Participants received two successive treatments (10% diclofenac gel or placebo gel) in random order over a 3-day period. There was a 1-week washout period between the treatments. Allocation was by simple randomisation, and the participants as well as the assessing/treating researcher were blinded to treatment allocation. OUTCOME MEASURES The primary outcome measure was pain level (0-10) during tendon loading (hopping). Secondary outcome measures included pain at rest, pressure pain threshold of the Achilles tendon and symptom improvement. RESULTS Nineteen adults participated in the study, and all were included in the analysis. Diclofenac gel significantly reduced the average pain during tendon loading (p<0.001) and at rest (p=0.031). The average baseline hopping pain was 4.8/10 (95% CI 3.92 to 5.68) and was reduced to 3.1/10 (2.35-3.85) by diclofenac. Pain at rest was decreased and pressure pain threshold increased with diclofenac treatment, but not with placebo gel. There were no observed or reported side effects of either treatment. CONCLUSIONS In this small, short-term study, diclofenac was able to improve symptoms and reduce pain during tendon loading in participants with CAT, whereas placebo gel was not. A future study of diclofenac as a supplement to rehabilitation, with longer follow-up and powered to detect a difference between diclofenac and placebo, is indicated. TRIAL REGISTRATION ISRCTN60151284, http://www.isrctn.com/ISRCTN60151284 ETHICS: UBC Clinical Research Ethics Board approval was obtained for this research. The certificate number of the ethics certificate of approval to conduct research is H15-00999.