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Understanding Hand Anatomy1
The anatomy of the hand is very complex. We depend on functioning hands in order to do many of our normal daily tasks.
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Bones and Joints
The bones of the hand provide support and flexibility to the soft tissues. They can be divided into three categories:
Carpal bones – A set of eight irregularly shaped bones. These are located in the wrist area.
Metacarpals – There are five metacarpals, each one related to a digit.
Phalanges – The bones of the fingers. Each finger has three phalanges, except for the thumb, which has two.
Joints are formed wherever two or more of these bones meet. Each of the fingers has three joints:
Metacarpophalangeal joint (MCP) – the joint at the base of the finger.
Proximal interphalangeal joint (PIP) – the joint in the middle of the finger.
Distal interphalangeal joint (DIP) – the joint closest to the fingertip.
The surfaces of the bones where they meet to form joints are covered with a layer of cartilage, which allows them to glide smoothly against one another as they move.
Ligaments and Tendons
The ligaments are tough bands of connective tissue that connect the bones to support them and keep them in place. Important ligaments of the hand are:
Collateral ligaments – finger and thumb joints, which prevent sideways movement of the joint.
- Volar plate – As the joint in the finger is straightened, this ligament tightens to keep the PIP joint from bending backward
- Radial and ulnar collateral ligaments – a pair of ligaments which bind the bones of the wrist and provide stability
- Volar radiocarpal ligaments – a complex web of ligaments that support the palm side of the wrist
- Dorsal radiocarpal ligaments – ligaments that support the back of the wrist
- Ulnocarpal and radioulnar ligaments – two sets of ligaments that provide the main support for the wrist
- Tendons are bands of connective tissue that attach the muscles to the bone enabling the muscles to move the bones.
The main tendons of the hand are:
- Superficialis tendons, which pass through the palm side of the wrist and hand, and attach at the bases of the middle phalanges. They act with the profundus tendons to flex the wrist and MCP and PIP joints.
- Profundus tendons, which pass through the palm side of the wrist and hand, and attach at the bases of the distal phalanges. They act with the superficialis tendons to flex the wrist and MCP and PIP joints. They also flex the DIP joints.
- Extensor tendons of the fingers, which attach to the middle and distal phalanges and extend the wrist, MCP, PIP and DIP joints.
- Flexor tendons, nine long tendons which pass from the forearm through the carpal tunnel of the wrist. They diverge in the palm, where two go to each finger (one attaches at the DIP and one at the MCP) and one goes to the thumb.
- Extensor pollicis brevis and abductor pollicis longus, which run from the muscles in the top of the forearm and enable movement of the thumb.