This chapter presents the key facts, clinical presentations, diagnostic testing, treatments, and prognosis of orthopedic infections and other complications such as septic arthritis, infectious tenosynovitis, clenched fist injuries, osteomyelitis, vertebral osteomyelitis and discitis, and compartment syndrome. Infection occurs primarily through hematogenous seeding of the joint (bacteremia). Contiguous soft-tissue infection or direct inoculation of the joint may play a part, albeit to a lesser extent. Risk factors include age, diabetes mellitus, rheumatoid arthritis, joint surgery, prosthetic joint, skin infection, intravenous drug use, and alcoholism. Symptoms and examination findings may be minimal in the setting of immunosuppression. Consider plain radiographs of the affected joint to exclude joint destruction or associated osteomyelitis. Infected joints require orthopedic surgery consultation for consideration of irrigation and debridement in the operating room. MRI is highly sensitive and specific for detecting bone marrow edema, cortical destruction, soft-tissue infection, and sinus tracts, even in early disease.