Kentaro Uchida,1 Shotaro Takano,1 Gen Inoue,1 Dai Iwase,1 Jun Aikawa,1 Ken Takata,1 Ryo Tazawa,1 Ayumu Kawakubo,1 Hiroyuki Sekiguchi,2 Masashi Takaso11Department of Orthopedic Surgery, Kitasato University School of Medicine, Sagamihara City, Kanagawa 252–0374, Japan; 2Shonan University of Medical Sciences Research Institute, Chigasaki City, Kanagawa 253–0083, JapanPurpose: While research suggests that obesity is a risk factor for knee osteoarthritis (KOA), the mechanisms are not fully understood. Mast cell (MC) numbers are increased in the osteoarthritic synovium and in the adipose tissue of obese individuals. We hypothesized that MC numbers are increased in the synovium of obese KOA patients. This study investigated MC marker and MC-generated cytokine/growth factor expression in the synovium of obese KOA patients.Patients and methods: Patients radiographically diagnosed with KOA (male: 38, female: 132) were allocated to three groups based on their body mass index (BMI): normal (