Each of the four fingers in a human hand has three joints. The hand contains 27 bones, eight of them in the wrist. The metacarpal bones, which make up the palm, include five bones. The five fingers and thumb count for the remaining 14 bones. Finger joints have distinct names. The hand attaches to the arm by the wrist joint, or carpus.
Each finger attaches to the palm or metacarpal by its carpometacarpal joint, or knuckle. The knuckles allow the fingers to bend. The knuckles or CMC joints of the fingers are numbered for the fingers. You start the number naming with the first finger next to thumb. This finger attaches to the hand by the first CMC joint. The fourth CMC joint connects the fourth finger, or pinky. The CMC of the thumb is distinctly different from the CMC of the four fingers.
Fingers are phalanges. Phalanges have three sections, the proximal phalange, the middle or intermediate phalange, and the distal phalange. The proximal phalange (first segment of the finger) connects to the hand by the CMC joint. At the top of the proximal phalange is the proximal interphalangeal joint. This joint connects the proximal phalange bone to the middle phalange bone. Each of these joints is named for the number of the finger. For instance, the first finger next to the thumb has the first proximal interphalangeal joint. The second finger on the hand has the second proximal interphalangeal joint, and so on.
The middle segment of the finger is called the middle phalange. Each middle phlanage is formally named by the number of the finger, one through four. The middle phalange has two joints on it. At the base or lower end of the middle phalange is the proximal interphalangeal joint. At the top of the middle phalange is the distal interphalangeal joint. The distal interphalangeal joint connects the top of the middle phalange to the distal phalange.
Distal and Proximal
The distal and proximal interphalangeal joints are similar in design. Distal joints are smaller than proximal joints but function the same. The tendons, ligaments and neurons attached to the finger joints connect in an elaborate system going through the hand and wrist to the arms. The movement of these joints happens through the body's command of the muscles, tendons and ligaments. The joints are designed to work exclusively at the command of the musculature of the hand.
Similarities and Differences
The interphalangeal and metacarpal joints are both capable of flexion and extension. Flexion is bending. It allows you to turn your fingers down and away from the palm to grasp. Extension is the straightening of the fingers to keep them in a plane with the palm. In addition, the metacarpal joints allow one other movement that the interphalangeal joints cannot. Knuckles or CMC joints allow abduction and adduction. Abduction is the spreading of the fingers apart. Adduction is the bringing of the fingers together.