Joint free bodies, also known as “joint rats”, are often indolent and immobile in the joints. It can be caused by occasional postures in which the joint is crossed and immobile. Free bodies are more common in the knee joint, mainly from exfoliative osteochondritis, synovial osteochondromatosis, bone fractures, articular surface fractures, and damaged menisci. Free bodies can be fibrinous, fibrous, or osteochondral. Fibrinous free bodies can be secondary to intra-articular hemorrhage with a polarized blood clot composition. Fibrous free bodies are often self-shedding hypertrophic synovial villi. Cartilaginous free bodies are mainly from trauma or various pathological conditions. For joint free bodies, arthroscopic surgery may be considered for removal.