Diarthrosis

Diarthrosis, also called a synovial joint, is a type of joint that permits a wide range of motion. It is characterized by a joint cavity that separates the two articular surfaces of the bones.

The joint is encased in an articular capsule composed of an outer fibrous layer and an inner synovial membrane. The articulating surfaces are covered with articular (hyaline) cartilage. The capsule and typically surrounding ligaments provide stability, while the synovial membrane produces synovial fluid that lubricates the joint. Some diarthroses contain additional structures such as menisci, articular discs, or bursae to enhance fit, stability, or shock absorption.

Diarthroses are classified by movement into uniaxial (hinge, pivot), biaxial (condyloid, saddle), and multiaxial (ball‑and‑socket). They are also described by the shapes of the articular surfaces: hinge (elbow), pivot (proximal radioulnar), condyloid (wrist), saddle (thumb), ball‑and‑socket (shoulder, hip), plane (gliding joints like the acromioclavicular). Movements include flexion, extension, abduction, adduction, rotation, circumduction, and gliding.

Development and function: Diarthroses develop from mesenchymal tissue and become encapsulated synovial joints. They provide a high degree of mobility while relying on ligaments, muscles, and the joint capsule for stability. Pathologies affecting diarthroses include osteoarthritis, rheumatoid arthritis, gout, and dislocations; assessment may involve imaging and analysis of synovial fluid.