Fluid in the sac, the synovial fluid , lubricates the joint. The fluid-filled sac of a knee or shoulder joint is called a bursa . When these joints are injured, the pain and inflammation is called bursitis . Tearing or overstretching of ligaments is called a sprain. Tendons, ligaments, and skeletal muscle are attached to the periosteum of bones at the joints.
Tendons are connective tissue that attach muscles to bones.
Ligaments are composed of tough bands of connective tissue, and hold together movable joints, connecting bone to bone. Skeletal muscles are responsible for bone movement, and are discussed further in the next section.