Objective To determine whether spa therapy, plus home exercises and usual medical treatment provides any benefit over exercises and usual treatment, in the management of knee osteoarthritis.

Methods Large multicentre randomised prospective clinical trial of patients with knee osteoarthritis according to the American College of Rheumatology criteria, attending French spa resorts as outpatients between June 2006 and April 2007. Zelen randomisation was used so patients were ignorant of the other group and spa personnel were not told which patients were participating. The main endpoint criteria were patient self-assessed. All patients continued usual treatments and performed daily standardised home exercises. The spa therapy group also received 18 days of spa therapy (massages, showers, mud and pool sessions).

Main Endpoint The number of patients achieving minimal clinically important improvement (MCII) at 6 months, defined as ≥19.9 mm on the visual analogue pain scale and/or ≥9.1 points in a normalised Western Ontario and McMaster Universities osteoarthritis index function score and no knee surgery.

Results The intention to treat analysis included 187 controls and 195 spa therapy patients. At 6 months, 99/195 (50.8%) spa group patients had MCII and 68/187 (36.4%) controls (χ²=8.05; df=1; p=0.005). However, no improvement in quality of life (Short Form 36) or patient acceptable symptom state was observed at 6 months.

Conclusion For patients with knee osteoarthritis a 3-week course of spa therapy together with home exercises and usual pharmacological treatments offers benefit after 6 months compared with exercises and usual treatment alone, and is well tolerated.

Trial registration number NCT00348777.