The purpose of this study is to validate the potential etiologic factors for temporomandibular disorder(TMD). TMJ arthroscopic examination was performed in upper joint compartment of 32 joints from 20 patients with mandibular fractures. Synovial fluid was collected from the upper joint space during pumping manipulation with normal saline. Cytologic smearing and histomorphologic exam of synovial fluid were performed in 15 joints. Prostaglandin $E_2(PGE_2)$ concentration was measured in 11 joints. Leukotriene $B_4(LTB_4)$ concentration was measured in 8 joints. There were several arthroscopic variables such as ecchymosis, fibrillation, and adhesion. Histomorphologic exam showed a variety of findings such as bloody smears, cellular cluster, degenerated cells and cartilage, undifferentiated crystal. Mean $PGE_2$ concentrations were 316.5 pg/ml. Mean LTB4 concentrations were 45.9pg/ml. This study demonstrated a variety of findings on inflammatory and degenerative changes of TMJ. Because acute trauma such as mandibular fracture is a major etiologic factor in cartilage degradation and biochemical and intraarticular pathology, clinicians must identify and address TMJ signs and symptoms during follow-up periods in the long term.