Anatomy: Hand and Wrist
Anatomy of the Hand
The wrist joint is the complex joint formed between the distal ends (furthest from the body) of the Radius and Ulna (two forearm bones) and the carpal bones. It connects the forearm to the hand and allows a good range of motion. Repetitive use does however frequently lead to injuries.
Bones and Articulation
The Ulna is the larger of the two forearm bones, although it tapers at the wrist end, to become narrower than the Radius at this point. The Radius is positioned on the thumb side of the wrist, and the ulna on the little finger side.
They form the wrist joint with the carpal bones. Altogether there are 8 carpal bone which are arranged in two rows, proximal and distal:
The scaphoid bone crosses both rows as it is the largest carpal bone. The scaphoid and the lunate are the two bones which actually articulate with the radius and ulna to form the wrist joint.
The human hand consists of a broad palm (metacarpus) with 5 digits, attached to the forearm by a joint called the wrist (carpus).
The four fingers on the hand are used for the outermost performance; these four digits can be folded over the palm which allows the grasping of objects. Each finger, starting with the one closest to the thumb, has a colloquial name to distinguish it from the others:
- Index finger, pointer finger, or forefinger
- Middle finger
- Ring finger
- Little finger or 'pinky'
The human hand has 27 bones: the carpals or wrist accounts for 8; the metacarpals or palm contains five; the remaining fourteen are digital bones; fingers and thumb.
The palm has five bones known as metacarpal bones, one to each of the 5 digits. These metacarpals have a head, a shaft, and a base.
Human hands contain fourteen digital bones, also called phalanges, or phalanx bones: two in the thumb (the thumb has no middle phalanx) and three in each of the four fingers. These are the distal phalanx, carrying the nail, the middle phalanx, and the proximal phalanx.
Sesamoid bones are small ossified nodes embedded in the tendons to provide extra leverage and reduce pressure on the underlying tissue. Many exist around the palm at the bases of the digits; the exact number varies between different people.
The articulation of the human hand is more complex and delicate than that of comparable organs in any other animal. Without this extra articulation, we would not be able to operate a wide variety of tools and devices, nor achieve the wide variety of possible hand gestures.
The articulations are:
- Interphalangeal articulations of hand (the hinge joints between the finger bones)
- Metacarpophalangeal joints (where the fingers meet the palm)
- Intercarpal articulations (where the palm meets the wrist)
- Wrist (may also be viewed as belonging to the forearm)