Objective: To examine the effects of pulsed short-wave diathermy (PSWD), delivered at an intensity sufficient to induce a thermal sensation and at an athermal intensity, in comparison with a placebo short-wave diathermy treatment, on reported pain, stiffness and functional ability and on mobility performance of patients with osteoarthritis of the knee.

Design: A placebo-controlled double-blind trial with sequential allocation of patients to different treatment groups.

Setting: Outpatient physiotherapy department.

Subjects: One hundred and three consecutive patients, mean age 73.7 (9 = 6.6) years with osteoarthritis of one or both knees for at least three months.

Interventions: All participants received three 20-min-long treatments per week for three weeks. One group received PSWD with mean power of 18 W (thermal effect), one group received PSWD with mean power of 1.8 W (athermal effect), and one group received sham short-wave diathermy treatment. Patients were assessed before the initial treatment, immediately following the last treatment, and at a three-month follow-up.

Main measures: Outcome measures included the WOMAC Osteoarthritis Index, which assessed reported pain, stiffness, and functional ability, and four measures of mobility performance: Timed Get Up and Go test (TGUG), stair-climbing, stairdescending and a 3-min walk.

Results: A difference across time was observed for the pain and stiffness categories of the WOMAC Osteoarthritis Index (p < 0.033 and p < 0.008, respectively), with no differences between groups. No other significant differences across time or between groups were observed in any of the other measures.

Conclusion: The findings do not demonstrate pulsed short-wave diathermy, as it is utilized in clinical settings, to be effective in the treatment of osteoarthritis of the knee.