The Wrist & Joints of the Hand

The Skeleton of the Hand

• Divided into 3 Anatomical Regions:
• Carpus - 8 short bones arranged into a proximal row (scaphoid, lunate, triquetral and pisiform) and a distal row (trapezium, trapezoid, capitate and hamate)
• Metacarpals (5)
• Phalanges (14 - 2 in the thumb and 3 in the remaining 4 digits)

The Wrist Joint

• Functionally the wrist is made up of the radiocarpal, midcarpal and intercarpal joints
• Anatomically the wrist is made up of the radiocarpal joint
• the proximal row of carpal bones (scaphoid, lunate and triquetral) 
• the radius and the fibrocartilagenous disc 

The Radiocarpal Joint

• Classified as  synovial ellipsoid joint
• Articular surfaces
• Inferior aspect of radius (note triangular and quadrilateral facet) covered in hyaline cartilage and inferior aspect of fibrocartilagenous disc - form biconcave surface
• Proximal aspect of scaphoid, lunate and triquetral (all covered with hyaline cartilage) - form biconvex surface

The Radiocarpal Joint - Capsule

• Series of irregular bands passing from distal end of radius and ulna anteriorly and posteriorly to articular margins of scaphoid, lunate and triquetral
• Medially and laterally extend from styloid processes of radius and ulna to sides of scaphoid (laterally) and triquetral (medially)
• Lined with synovial membrane

Palmar (Volar) Ligaments

• Series of thickenings across the anterior capsule
• Anatomically divided into 
• Palmar radiocarpal ligament passing from anterior radius to proximal row and capitate
• Palmar ulnocarpal ligament passing from disc and ulnar styloid to proximal row (mostly triquetral and lunate) 

Dorsal Radiocarpal Ligament

• From posterior lower radius to proximal row of carpal bones (scaphoid, lunate and triquetral)
• Weak and more commonly injured
• Palmar ligaments limit extension while dorsal ligaments limit flexion 

Collateral Ligaments

• Limit abduction / adduction of the wrist
• Radial collateral - flat band from apex of radial styloid to lateral scaphoid
• Ulnar collateral - cord from apex of ulnar styloid to triquetral and pisiform

Joints of the Carpal Bones

• Series of synovial plane joints between adjacent bones forming part of the functional wrist joint
• Produce a small amount of gliding to allow normal movements at the wrist:
• Joints of the proximal row - between scaphoid/lunate, lunate/triquetral and triquetral / pisiform
• Joints of the distal row - between trapezium / trapezoid, trapezoid / capitate and capitate / hamate
• All reinforced by palmar, dorsal and interosseus ligaments 

Midcarpal Joint

• Formed between the proximal row (scaphoid, lunate and triquetral) and the distal row (trapezium, trapezoid, capitate and hamate)
• Class - synovial compound, biaxial joint
• Forms an irregular joint line - S shape from medial to lateral
• All articular surfaces covered with hyaline cartilage
• Surrounded by a capsule (irregular bands of fibres) which is lined with an irregular synovial membrane

Ligaments of the Midcarpal Joint

• Palmar Intercarpal  ligaments - strong bands passing from the capitate to the proximal row of bones
• 2 main bands (pictured) pass to scaphoid and triquetral
• A thinner band passes from capitate to lunate - a potentially weak space which may allow lunate or capitate to dislocate anteriorly

Dorsal Intercarpal Ligaments

• Short series of fibres uniting adjacent bones
• Weak and more prone to injury than the anterior ligaments

Collateral Ligaments

• Midcarpal joint is further reinforced by collateral fibrous bands limiting abduction / adduction:
• Radial collateral ligament - continuation of the RC ligament of the radiocarpal joint - strong, flat band passing from scaphoid to trapezium
• Ulnar collateral ligament - from triquetral to hamate
• Both often included as part of the palmar intercarpal ligaments

Movements of the Functional Wrist

• Movements occur at both the radiocarpal joint and midcarpal but in varying degrees

Surface Anatomy

• Wrist - a line, concave distally passing from the apex of the radial styloid to the ulnar styloid
• Midcarpal - identified by palpating the distal line of scaphoid and proximal capitate/hamate

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