Chiro.Org Blog:

The general stability of synovial joints is established by action of surrounding muscles. Excessive joint stress results in strained muscles and tendons and sprained or ruptured ligaments and capsules. When stress is chronic, degenerative changes occur. The lining of synovial joints is slightly phagocytic, is regenerative if damaged, and secretes synovial fluid that is a nutritive lubricant having bacteriostatic and anticoagulant characteristics. This anticoagulant effect may result in poor callus formation in intra-articular fractures where the fracture line is exposed to synovial fluid. Synovial versus mechanical causes of joint pain are shown in Table 1.