Background: Knee osteoarthritis (OA) is prevalent and associated with both pain and functional disability. Current treatments aim to alleviate mild to moderate symptoms by various methods. Topical capsaicin (0.075% and 0.05%) has been evaluated for the treatment of the painful joints. A burning sensation was the most common side effect at these strengths. Therefore, the authors aimed to evaluate the efficacy of 0.0125% capsaicin gel (Capsika gel) compared to a placebo (the vehicle gel) in patients with symptomatic OA knee.
Material and method: This was a cross-over; double blinded, randomized, controlled trial of 100 patients with mild to moderate knee OA. All of the patients received either capsaicin gel or placebo gel applied to the affected knee, three times daily for 4 weeks with one week washout period after which the treatment switched to either capsaicin gel or placebo gel for the next 4 weeks. A blinded examiner used the visual analog scale (VAS) and WOMAC score to do weekly assessments.
Results: Subjects averaged 61 years of age (range, 44 to 82). During the enrollment phase, only female farmers presented. Mean body weight and height was 62.97 +/- 10.25 kg and 1.54 +/- 0.053 m, respectively The respective baseline VAS and WOMAC score was 6.40 +/- 1.64 and 51.65 +/- 13.3. The severity of OA, according to the KL criteria was: 83 patients with grade 2 and 16 with grade 3. The respective mean difference of VAS and total WOMAC score in the capsaicin group vs. the placebo group was statistically significant (p < 0.05). The mean difference of the WOMAC pain, stiffness and functional subscales in the capsaicin vs. the placebo group was also significant (p < 0.05). The only adverse event reported was a burning sensation. During the 4-week treatment with capsaicin, approximately 67% of patients had a burning sensation but none withdrew for this reason.
Conclusion: 0.0125% capsaicin gel was an effective treatment in mildly to moderately painful OA knees. The burning sensation reported by patients in the capsaicin group was less disturbing than in previous studies and none of the present patients withdrew for this reason.