The effect of either topical menthol or a placebo on functioning and knee pain among patients with knee OA

Osteoarthritis (OA) is a common health problem with symptoms including reduced functioning and joint pain. Protracted pharmacological management of knee OA is associated with side effects including gastrointestinal, renal, and neurological dysfunction. Menthol gels have been used with limited empirical support to relieve pain and improve functioning among individual with OA. The purpose of this study was to compare the ability to complete functional tasks and knee pain while completing functional tasks among patients with knee OA after topical application of either 3.5% menthol gel or an inert placebo gel. Twenty individuals with knee OA volunteered to complete 2 data collection visits 1 week apart. Subjects underwent the same data collection at each visit including the performance of functional tasks and self-reporting knee pain while performing each task. The functional tasks included a 6-Minute Walk (6-MW), the Timed Get Up and Go (TUG), 30-second timed chair stand (TCS), and time to ascend (Up stairs) and descend (Down stairs) a flight of stairs. Subjects reported their knee pain immediately following each functional task using a 100-mm visual analog scale. These assessments of pain and functioning were measured twice at each subject visit: upon arrival at the facility without any intervention and again during the same visit after random application to the OA knee of 5 mL of 3.5% menthol gel or 5 mL of an inert gel. There were no significant between-group differences or time by treatment interaction in performance of any of the functional tasks, or measures of pain, at any of the data collection time points. However, there were significant within-group differences. Scores on the 6-MW, TCS, and Down stairs functional tasks improved significantly following the application of menthol gel. Scores on the Down stairs functional task improved significantly following application of the placebo gel. The menthol intervention resulted in significant reductions in pain during the TUG, TCS, Up stairs, and Down stairs tasks. The placebo condition did not result in any significant changes in pain during the functional tasks. There were no differences detected in functional tasks or pain following the placebo and menthol conditions. These findings provide partial support regarding the efficacy of menthol gel to improve functioning and reduce pain among knee OA patients.