In human anatomy, the wrist is variously defined as the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand. The wrist joint (also known as the radiocarpal joint) is a synovial joint in the upper limb, marking the area of transition between the forearm and the hand. The wrist is a complex joint that bridges the hand to the forearm. It is actually a collection of multiple bones and joints. The bones comprising the wrist include the distal ends of the radius and ulna, 8 carpal bones, and the proximal portions of the 5 metacarpal bones.
Wrist joint supports movement of hand and forearm. Sports and manual work involves complicated and coordinated activities of the hand and wrist joint. Wrist joint is second most active joint after ankle joint. Wrist joint is a perfect geometrical pattern that matches convex shape of carpal bones with concave articulating surface of radius. Ulnar bone is not in contact with carpal bone at rest, but during supination and pronation, the carpal bone gets linked to ulna to optimize the rotation.
Bones of Wrist Joint:
Wrist joint is a flexible joint and involves 15 bones in forming three sections of wrist Joint.
Proximal Wrist Joint: Proximal wrist joint is a pivot joint formed by radius and ulna. Head of distal end of ulna lies against ulnar notch of radius bone. The link between ulna and radius is covered with smooth cartilages. Joint is covered by synovial capsule. Capsule is lax around the joint which allows semi-rotation of joint during pronation and supination.
- First link is between Radius and Ulna with proximal row of 3 carpal bones. The three carpal bones of proximal row are Scaphoid, Lunate and Triquetrum. The joint is also known as ellipsoid joint. Distal end of Ulna comes in contact with Triquetrum during ulnar deviation or adduction movement of wrist joint.
- Second link is between proximal and distal row of carpal bones, also known as inter-carpal wrist joint. Trapezium, Trapezoid, Capitate, Hamate and Pisiform form distal rows of carpal bones and are linked with proximal 3 carpal bones to form intermediate wrist joint.
Distal Wrist Joint: Distal row of carpal bones Trapezium, Trapezoid, Capitate, Hamate and Pisiform are linked with five metacarpal bones.
Synovial Membrane Capsule: Synovial membrane is a thin connective tissue. Synovial membrane produces viscous lubricating fluid. Synovium covers all three sections of wrist joint. Lax synovial capsule allows following wrist joint movements.
Wrist Joint Movements:
- Wrist Flexion Movement or Forward Bend of the Wrist Joint. Bending the palm downwards towards the wrist is called Wrist Flexion
- Wrist Extension Movement or Backward Bend of the Wrist Joint. Bending the palm upwards with fingers facing the sky is called Wrist Extension.
- Wrist Abduction Movement (Radial Deviation) or Sideward Bend of the Wrist Joint. Bending the wrist away from body on the side of the thumb while palm facing upward is called wrist abduction or radial deviation.
- Wrist Adduction Movement (Ulnar Deviation) or Sideward Bend of the Wrist Joint. Bending the wrist towards the body while palm is facing upward is called Wrist Adduction or Ulnar Deviation.