This systematic review with meta-analysis for 36 randomized placebo-controlled trials looked at the efficacy of physical modalities (transcutaneous electrical stimulation - TENS, electro-acupuncture - EA, pulsed electromagnetic fields - PEMF, ultrasound - US, and low level laser treatment - LLLT) in patients with knee osteoarthritis (OA) pain within 1-4 weeks and at follow-up at 1-12 weeks after the treatment. The 36 RCTs identified had 2434 patients with a mean age of 65.1 years (1391 patients received active treatment). Results indicated that the optimal doses of TENS, EA and LLLT appear to offer short-term pain relief for knee OA.