Anatomy of the Wrist

The wrist connects the lower arm with the hand.  The wrist allows us to use our hands in many ways and in many positions.  Everyday tasks depend on the wrist and would be difficult to impossible to do if the wrist isn’t working as it should.

The wrist is a complex joint comprised of bones, joints, muscles, soft tissues (ligaments, tendons, and cartilage), bursae, nerves, and blood vessels.  All of these work together to provide a wide range of motion and the strength necessary for normal wrist function involved in gripping and in rotating the hand up and down and from side to side.

Bones and Joints

The wrist is made up of eight carpal bones that are arranged in two rows.  The lunate, triquetral or triquetrum, and pisiform bones are in the proximal row.  The trapezium, trapezoid, capitate, and hamate bones are in the distal row.  Because it is the largest carpal bone, the scaphoid crosses both rows.    Every carpal bone forms a joint with the bone next to it.  The carpal bones connect the hand’s metacarpal bones and the forearm’s radius and ulna bones.

The wrist joint is a kind of pivot joint that is made up of many small joints.  It is formed by the radius and ulna, and the carpal bones.  The concave shape of the head of the radius bone allows the carpal bones to rotate and pivot with the end of the bone.

Muscles

The muscles that are important to the wrist are actually located in the forearm.  Their tendons cross the wrist joint and a go into the hand.  They control the actions of the fingers, thumb, and wrist.  Muscles on the back of the forearm work to extend or pull back the wrist.  Muscles on the front of the forearm work to flex the wrist.  Forearm muscles also work to tilt the wrist so that the thumb leads (radial deviation) or so that the fifth finger leads (ulnar deviation).

Soft Tissues

Ligaments attach bones to bones.  Tendons attach muscle to bones.  Ligaments and tendons are both made of collagen fibers that are bundled together.  The bundles come in various sizes and thicknesses to provide different degrees of strength.  Articular cartilage covers the ends of bones at any joint.  It absorbs shock and allows joint surfaces to safely move against each other, making motion easier.

Every bone in the wrist is joined to the one next to it by at least one ligament.  These ligaments form watertight sacs that contain lubricating fluid (synovial fluid).  A sac, or joint capsule, surrounds and supports the carpal bones in the wrist.

Two of the largest and most important wrist ligaments are the ulnar and the radial collateral ligaments.  They support the sides of the wrist.  The ulnar collateral ligament (UCL) crosses the side of the wrist that is away from the thumb.  It helps keep the wrist from bending too far to the side, toward the thumb.  The radial collateral ligament (RCL) is on the thumb side of the wrist.  It helps keep the wrist from bending too far to the side, away from the thumb.

Several important tendons that cross the wrist start as muscles in the forearm.  Flexor tendons on the palm side of the wrist curl the fingers and thumb.  They also bend the wrist.  Extensor tendons on the back of the wrist allow the fingers and thumb to be straightened.

Articular cartilage covers the sides of the wrist’s carpal bones as well as the ends of the connecting bones from the forearm to the fingers and thumb.  A small cartilage pad (triangular fibrocartilage complex or TFCC) is located between the ulna and the lunate and the triquetrum.  The pad provides cushioning for this area of the wrist joint and improves the gliding action and the range of motion within the wrist joint.

Bursae

Bursae are located throughout the body.  A bursa is a small sac of lubricating fluid that is found between two moving surfaces.  The wrist has two bursas.  The radial bursa is around the thumb and runs to the wrist’s crease.  The ulnar bursa is around the tendons of the ring, middle, and index fingers.

Nerves and Blood Vessels

There are three nerves that travel from the forearm, across the wrist, and into the hand.  They carry messages from the brain to the muscles that move the arm, hand, fingers, and thumb.  They carry messages about touch, temperature, and pain back to the brain.

  • The radial nerve is on the thumb side of the wrist joint.  It gives feeling to the back of the hand from the thumb to the third finger.
  • The median nerve goes through the carpal tunnel.  It divides into four branches that give feeling to the thumb, the second and third fingers, and the inside half of the fourth finger.  It also sends a nerve branch to the thumb’s thenar muscles.  They assist in moving the thumb and allow one to touch the thumb’s pad to the other fingertips on the same hand.
  • The ulnar nerve goes through Guyon’s canal which is formed by two carpal bones and their connecting ligament.  Its branches give feeling to the fifth finger and the outer half of the fourth finger.  In addition, they go to the small muscles in the palm and to the muscle that pulls the thumb toward the palm.

Blood vessels that supply the hand with blood travel with the nerves.  The radial artery is the largest.  It goes across the front of the wrist, close to the thumb.  It is where the pulse is taken in the wrist.  Like the ulnar nerve, the ulnar artery goes through Guyon’s canal.  The ulnar and radial arteries supply blood to the front of the hand and fingers.  Other arteries go across the back of the wrist to supply blood to the back of the hand and fingers.

If you are feeling any type of wrist pain or discomfort, please schedule a consultation at Jacksonville Orthopaedic Institute Beaches.  One of our highly-skilled surgeons will be happy to discuss your pain, your lifestyle, and the steps necessary to ensure that you are back to your best self.  Contact us today at 904-241-1204 or online at www.joibeaches.com!

Request Appointment
...................................................................................................

Exclusive Sports Medicine Provider for:

Jacksonville JaguarsJacksonville Sharks
Jacksonville University

FSCJ Blue Wave