Joint Biomechanics - Wrist and Hand Flashcards
The Wrist Articulations
Two primary articulations within the wrist are radiocarpal and midcarpal joints.
Intercarpal joints.
What are the important functions of the wrist?
Provide optimal position of the hand.
Load acceptance
Kinematics of pronation and supination of the forearm.
Radiocarpal Joint
Between the radius,TFCC (proximal) and mostly scaphoid and lunate, triquetrum (distal)
Ellipsoidal: Biplanar - sagittal/frontal (NOT pronation/supination).
Concave surface: Radial articular surface
Convex: Carpal bones
Convex moving on concave - Roll and slide in opposite direction (in both flexion/extension and ulnar/radial deviation).
Midcarpal Joint
Ellipsoidal
Between the proximal and distal rows of carpal bones.
Intercarpal Joints
Plane joints
13 separate intercarpal articulation can be identified.
With midcarpal joint, contribute to wrist motion through small gliding and rotary motions, occurring primarily between the bones within the proximal row, stretch several ligaments that dissipate compressive force.
Wrist Ligaments
Essential to maintaining the natural intercarpal alignment and transferring forces within and across the carpus.
Muscle-produced forces stored in stretched ligaments provide important control to the complex arthrokinematics of the wrist.
Structures of the Triangular Fibrocartilage Complex (TFCC)
- Articular Disc (triangular fibrocartilage)
- Distal radio-ulnar joint capsular ligament
- Palmar ulnocarpal ligament (ulnotriquetral, ulnolunate)
- Ulnar collateral ligament
- Fascial sheath that encloses the tendon of the extensor carpi ulnaris.
Triangular Fibrocartilage Complex (TFCC)
Primary component is the articular disc (within both distal radioulnar and radiocarpal joints).
Proximal surface accepts the ulna at the distal RU joint.
Distal surface accepts the convex surfaces of a part of the lunate and triquetrum at the RC joint.
The central 80% is avascular with poor healing potential.
What are the main functions of the Triangular Fibrocartilage Complex (TFCC)
- Stability of the distal RUJ while permitting radial rotation on fixed ulna.
- Transfer about 20% of compression forces from hand to forearm.
Wrist Arthrokinematics - Sagittal Plane
Double joint system, with movement occurring simultaneously at both the radiocarpal and midcarpal joints.
Central column formed by linkages between the distal radius, lunate, capitate, and third metacarpal.
Total ROM achieved by moderate amounts of rotation at the individual joints.
Wrist Arthrokinematics - Frontal Plane
Ulnar deviation: limited by the contact of the triquetrum on TFCC and soft tissue tension.
Radial deviation: limited because the radial side of the carpus impinges against the styloid process of the radius.
Normal Forearm and Wrist Range of Motion
Wrist flexion: 80° Wrist extension: 60° Wrist ulnar deviation: 30° Wrist radial deviation: 20° Forearm pronation: 80-90° Forearm supination: 75-80° Elbow flexion: 145° Elbow extension: 0°
Wrist Flexors and Extensors
- Tendons of the primary muscles attach distally within the carpus, or the adjacent proximal end of the metacarpals; these muscles act essentially on the wrist only.
- Tendons of the secondary muscles cross the carpus as they continue distally to attach to the digits. Secondary muscles therefore act on the wrist and hand.
Synergists - Wrist Flexors
Primary: - Flexor carpi radialis - Flexor carpi ulnaris - Palmaris longus Secondary: - Flexor digitorum profundus - Flexor digitorum superficialis - Flexor pollicis longus - Abductor pollicis longus - Extensor pollicis brevis
Synergists - Wrist Extensors
Primary: - Extensor carpi radialis longus - Extensor carpi radialis brevis - Extensor carpi ulnaris Secondary: - Extensor digitorum - Extensor indicis - Extensor digiti minimi - Extensor pollicis longus
