Combined treatment with chondroitin sulfate and glucosamine sulfate shows no superiority over placebo for reduction of joint pain and functional impairment in patients with knee osteoarthritis: a six-month multicenter, randomized, double-blind, placebo-controlled clinical trial - Roman-Blas, J A; Castaneda, S; Sanchez-Pernaute, O (Arthritis Rheumatol, 2017)