Movement Science Week 5 - Wrist

Wrist Anatomy

• The wrist, also known as the carpus, is made up of 8 carpal bones.
• There are 3 joints that make up the wrist: the distal radioulnar joint, radiocarpal joint, and midcarpal joint.
• The radial bone is larger distally than the ulna.
• The ulnar styloid process and the styloid process of the radius are easily palpated.
• The tubercle of the radius is important because it divides the extensor carpi radialis brevis tendon from the extensor pollicis longus tendon.
• Ulnar tilt, which is an angulation at the distal radioulnar joint, facilitates ulnar deviation and limits radial deviation.
• The radius is tilted slightly toward the palmar side of the hand, known as palmar tilt, contributing to greater wrist flexion than extension.

Carpal Bones

• Scaphoid: Named for its boat-like shape, it articulates with the radius, capitate, trapezium, trapezoid, and lunate.
• Lunate: Moon-shaped bone; the most commonly dislocated carpal bone due to its lack of muscular attachments.
• Triquetrum: Triangular bone located in the most ulnar position.
• Pisiform: Located on the palmar surface of the hand and articulates with the triquetrum.
• Hamate: Medial bone in the distal row. It has a hook on the palmar side.
• Capitate: Central pillar of the wrist; the largest carpal bone, articulates with 7 other bones, including the hamate, lunate, scaphoid, trapezoid, and 3 metacarpals.
• Trapezoid: Sits between the trapezium and capitate.
• Trapezium: Asymmetrically shaped bone located under the thumb.

Wrist Joints

• Radiocarpal Joint: About 80% of forces applied to the hand are transmitted through the radius and only 20% through the ulna.
• Midcarpal Joint: Divided into the medial and lateral compartments. Arthrokinematics primarily occur here, with limited movements in the lateral compartment.

Wrist Motions

• Flexion/Extension: Occur through the medial/lateral axis and the capitate is the center of motion.
• Ulnar/Radial Deviation: Occur through the anterior/posterior axis and involve the capitate.
• Axial Rotation: Not a primary motion of the wrist, but can occur to a limited extent.
• Arthrokinematics:
  • During wrist extension, the lunate rolls dorsally and slides palmarly while the capitate rolls dorsally and slides palmarly.
  • During wrist flexion, the lunate rolls palmarly and slides dorsally while the capitate rolls palmarly and slides dorsally.
• The radiocarpal joint and midcarpal joint contribute equally to wrist motion.
• During ulnar deviation, the luminate and scaphoid roll towards the ulnar side with a palmar slide, and the same movement occurs at the proximal radioulnar joint.
• During radial deviation, the luminate and scaphoid roll towards the radial side with an ulnar slide.
• The scaphoid bumping against the styloid process of the ulna limits radial deviation, with 85% of radial deviation occurring at the midcarpal joint.