Section through a hip joint. The hip joint, a synovial joint, is of the ball-and-socket type, the head of the femur articulating with the cup-shaped acetabulum. The joint cavity is enclosed by a fibrous capsule lined with a type of connective tissue (synovial membrane) that produces a fluid (synovial fluid) that lubricates the cartilage-covered opposing surfaces of bone. The fibrous capsule is made up of internal circular fibres (zona orbicularis) and external longitudinal fibres, strengthened by ligaments, and covered by muscles.
joint, Structure connecting two or more bones. Most joints, including synovial (fluid-containing) joints and those between vertebrae, which incorporate a disk, can move. Immovable joints include the sutures of the skull (see fontanel). Ligaments connect the bones of a joint, but muscles keep them in place. Joint disorders include various forms of arthritis, injuries (e.g., sprains, fractures, and dislocations), congenital disorders, and vitamin deficiencies.