Tendons connect muscle to bone, so that when muscles contract they exert a force on the bone via the tendon; causing movement. Many tendons have to go around joints or over bony prominences, particularly in the foot. In order for these to glide properly, there is a soft tissue sheath rather like a tunnel which surrounds the tendon. The sheath produces a fluid (synovial fluid) which allows the tendon to glide smoothly preventing damage. However, they can become inflamed and produce excess fluid which results in a condition known as tenosynovitis.