The wrist contains a total of three joints. This makes the wrist much more stable, similar to having only one joint. The joints also give your wrist and hand a wide range of movement. Furthermore, the wrist joints let your wrist move your hand up and down, for example, when lifting your hand to wave around. These joints give you the ability to bend your wrist forward and backward, side to side, and rotate your entire hand. The three wrist joints are known as the radiocarpal joint, ulnocarpal joint, and distal radioulnar joint:
- Radiocarpal joint – This is where the radius (the thicker forearm bone) connects the bottom row of your wrist bones, which are the scaphoid, lunate, and triquetrum bones. This joint is mainly on the thumb side of your wrist.
- Ulnocarpal joint – This is the joint between the ulna (the thinner forearm bone) and the lunate and triquetrum wrist bones. The ulnocarpal joint is located on the pinky side of your wrist.
- Distal radioulnar joint – This joint is in the wrist but does not include the wrist bones. It connects the bottom ends of the radius and ulna.
The flexor carpi ulnaris (FCU) is on the palmar side of the wrist located on the small finger side. The FCU is one of the major muscles that flex the wrist. Occasionally, a direct blow or overuse can cause damage and pain to the FCU muscle and tendon. An injury to the FCU tendon is basically an injury to your muscle. The flexor muscles are the muscles that allow you to bend your fingers. These muscles are able to move your fingers through tendons, which are cord-like extensions that connect your muscle to your bone.