Anatomy of the Wrist

Intro
The anatomy of the wrist joint is extremely complex, probably the most complex of all the joints in the body.  The wrist is actually a collection of many bones and joints.  These bones and joints let us use our hands in a lot of different ways.   Our wrists need to be extremely mobile to allow our hands a full range of motion, but at the same time, the wrist must provide a good amount of strength.
Important Structures
The important structures of the wrist can be divided into several categories:
  • Bones and Joints
  • Ligaments and Tendons
  • Muscles
  • Nerves
  • Blood Vessels
Bones and Joints
There are 15 bones that form connections from the end of the forearm to the hand.  The wrist itself contains eight small bones, called Carpal Bones.   These bones are grouped in two rows across the wrist:
  1. Proximal Row – Where the wrist creases when you bend it.  Beginning with the thumb side of the wrist, the proximal row of carpal bones is made of the scaphoid, lunate, and triquetrum.
  2. Distal Row- Meets the proximal row a little further towards the fingers.  The distal row is made up of the trapezium, trapezoid, capitate, hamate, and pisiform bones.
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The proximal row of carpal bones connects the two bones of the forearm, the radius and the ulna,  to the bones of the hand.  The bones of the hand are called the metacarpal bones.  These are the long bones that lie within the palm of the hand.  The metacarpals attach to the phalanges, which are the bones in the fingers and thumb.
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* One reason that the wrist is so complicated is because every small carpal bone forms a joint with a bone next to it.  This means that what we call the wrist joint is actually made of many small joints.
Cartilage
Articular Cartilage is the material that covers the ends of the bones of any joint.   Articular cartilage can be up to one quarter of an inch thick in the large, weight bearing joints.  It is thinner in joints such as the wrist that don’t support a lot of weight.
The function of the articular cartilage is to absorb shock and provide an extremely smooth surface to make motion easier.  We have articular cartilage essentially everywhere that two boney surfaces move agains one another.  In the wrist, articular cartilage covers the sides of all the carpals and the ends of the bones that connect from the forearm to the finger.
Ligaments and Tendons
Ligaments are soft tissue structures that connect bones to bones.  The ligaments around a joint usually combine to form a joint capsule.  A joint capsule is a watertight sac that surrounds a joint and contains lubricating fluid called synovial fluid.  In the wrist, the eight carpal bones are surrounded and supported by a joint capsule.
There are two important ligaments that support the sides of the wrist call the collateral ligaments.
  • Ulnar Collateral Ligament (UCL) is on the ulnar side of the wrist.  It crosses the ulnar edge (the side away from the thumb) The UCL stabilizes and keeps the wrist from bending too far to the side (towards the thumb)
  • Radial Collateral Ligament (RCL) is on the thumb side of the wrist. The RCL prevents the wrist from bending too far to the side (away from the thumb)
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Movement of the wrist
There are four different movements of the wrist:
  • Abduction – Bending the thumb side of the hand toward the thumb side of the forearm
  • Adduction – Bending the pinky side of the hand toward the little finger side of the forearm
  • Flexion –  If your palm is facing down and you bend your wrist towards the floor
  • Extension – If your palm is facing down and you bend your wrist towards the sky
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The movement that will most likely cause pain in the wrist is extension.   Most people spend a lot of time every day with their wrist in mild extension (ex. hands at a keyboard).  The hand has its most powerful grip with the wrist in mild extension.  The wrist spends very little time in full flexion or full extension and like any join, will lost any part of it’s range of motion that isn’t used regularly. Most people gradually lose the ability to move easily and safely into full wrist extension.
Wrist Pain
A lot of wrist pain and discomfort is caused by soft tissue strain that occurs when the ligaments and tendons are forced into extension beyond their customary range.
If students complain of wrist pain a good recommendation would be to scale back on poses that bear weight onto the hands.   You can also vary the degree of extension of your wrists.  If placing the heels of your hands directly below your shoulders feels too intense, you can move your hands out a little in from of your shoulders, reducing the amount of extension.   As the wrists stretch out over time, begin to work them back beneath the shoulders.   As the wrists gain range of motion and endurance, more weight can be put on them.
Increasing wrist flexibility may help you avoid problems down the road.  Strengthen this key joint with these yoga poses!