Wrist Anatomy and Function Quiz

Biomechanics 2 Course Information

• Course title: Biomechanics 2
• Lecturer: Dr. Amany Gomaa Atiaa
• Affiliation: Lecturer of Burn & Surgery, Faculty of Physical Therapy, Sinai University
• Website: sinaiuniversity.net

Biomechanics of the Wrist Joint

• Components: Wrist complex, ligaments, muscles
• Positions: Loose packed position, close packed position
• Other features: Angles, arthrokinematics

Wrist Complex and Articulations

• Structure: Multiple articulations of eight carpal bones, distal radius, ulnocarpal space structures, metacarpals, and each other.

Bony Structure

• Division: The carpus is divided into proximal and distal rows.
• Distal row: Trapezium, trapezoid, capitate, and hamate (relatively immobile)
• Distal function: Forms carpometacarpal joint.
• Proximal row: Scaphoid, lunate, and triquetrum (more mobile)
• Proximal function: Forms radiocarpal joint with the distal radius.

Wrist Joint Components

• Distal radioulnar joint: synovial pivot
• Radiocarpal joint: condyloid synovial
• Midcarpal joint: synovial gliding
• Additional parts: ulnocarpal, carpometacarpal (saddle joint), and intercarpal joints

Triangular Fibrocartilage Complex (TFCC)

• Function: Load-bearing structure between the lunate, triquetrum, and ulnar head, stabilizes the ulnar aspect of the wrist.
• Injury risk: Acute or chronic degenerative injury.
• Diagnosis: Gold standard is arthroscopy, sometimes MRI reveals abnormalities.

Radius and Ulna

• Radius angle: Distal end angles 25 degrees toward the ulnar (medial) direction, allowing greater ulnar deviation than radial deviation.
• Radius angle limitation: Bony impingement of carpal (wrist) side against the styloid process of the radius limits radial deviation.
• Ulna angle: Distal articular surface angles 10 degrees in the palmar direction. This tilt influences wrist flexion.

Angles

• Sagittal plane: 10 degrees, range of flexion
• Frontal plane: 25 degrees, range of ulnar deviation.

Radiocarpal Joint

• Proximal component: Biconcave distal end of the radius and articular disc
• Distal component: Biconvex proximal row of carpal (scaphoid, lunate, triquetrum).
• Radiocarpal role of triquetrum: At full ulnar deviation, the medial surface of the triquetrum contacts the articular disc.
• Joint type: Convex on concave; important for mobilization.
• Force distribution: 20% of compression passes through the articular disc, 80% passes through the scaphoid and lunate to the radius.
• Largest contact region: When the wrist is slightly extended (10° ) and slightly deviated in the ulnar direction.

Wrist Joint Positions

• Close packed position: Extension with slight abduction/radial deviation.
• Loose packed position: Neutral wrist with slight abduction/ulnar deviation.

Wrist Ligaments

• Extrinsic ligaments: Attach carpal bones to the radius/metacarpals. Includes volar and dorsal ligaments; palmar radiocarpal, dorsal radiocarpal, radial collateral, ulnar collateral.
• Three important dorsal extrinsic ligaments: dorsal intercarpal, dorsal radiotriquetral, and dorsal radioulnar.
• Intrinsic ligaments: Originate and insert on carpal bones, including scapholunate interosseous, lunotriquetral interosseous, and scaphotrapeziotrapezoid.

Wrist Muscles

• Primary set: Act on the wrist only, tendons attach distally.
• Secondary set: Tendons cross the carpus to attach to the digits (act on the wrist and hand).
• Extensor muscles (primary/secondary): E.g., extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris, extensor digitorum, extensor indicis, extensor digiti minimi, extensor pollicis longus.
• Flexor muscles (primary/secondary): Includes flexor carpi radialis, flexor carpi ulnaris, palmaris longus, flexor digitorum profundus, flexor digitorum superficialis, flexor pollicis longus, abductor pollicis longus, extensor pollicis brevis

Wrist Movements

• Flexion: Anterior movement of the wrist or hand
• Extension: Posterior movement of the wrist or hand
• Radial deviation: Abduction of the hand
• Ulnar deviation: Adduction of the hand

Wrist Kinematics and Kinetics

• Osteokinematics: Wrist has two degrees of freedom (flexion/extension and ulnar/radial deviation)
• Circumduction: Combination of the aforementioned movements.
• Axis of rotation: Passes through the head of the capitate.
• Kinetics of Force Transmission: In extension, scaphoid transmits 51% of force, lunate transmits 49%. In neutral, it is 53% and 47%, and in flexion 55% and 45% respectively.

Wrist and Hand Injuries

• Ligamentous sprain: Scapholunate ligament injury, TFCC injury
• Fracture of distal radius
• Fractures of scaphoid and lunate.
• De Quervain's tenosynovitis (thickening of tendon sheaths/pain)
• Carpal tunnel syndrome (median nerve compression)

Contacting the Lecturer

• Email: [email protected]