Wrist joint

kinematics

· motion in two planes

· flexion-extension (dorsiflexion and palmarflexion)

· abduction-adduction (radial and ulnar deviation)

· combinations possible

· circumduction

· pronation and supination occur between radius and ulna

· three groups of tendons

· extrinsics of fingers

· flexors and extensors of wrist

· tendons around radial styloid

· proximal carpal row important

· no muscle insertions

· acts as intercalated segment in 3-joint system

· stability depends on ligamentous structures

· would tend to collapse into zig-zag

· prevented by scaphoid which crosses mid-carpal joint

Axes of motion

· centre of rotation is in capitate

· in AP, axis of rotation passes

· along MC III

· through capitate

· along radial aspect of lunate

· to centre of lunate fossa of radius

· in lateral, axis of rotation passes

· through longitundinal axis of capitate, lunate, radius

· at 45^o to longitudinal axis of scaphoid

Flexion-extension

· normal arc is 150^o

· 80^o palmarflexion

· 70^o dorsiflexion

· 10^o increased flexion due to volar tilt of distal radius

· contributions between midcarpal and radiocarpal joints

· palmarflexion - 2/5 at radiocarpal joint

· dorsiflexion - 2/3 at radiocarpal joint

Radial-ulnar deviation

· total arc is 60^o

· 20^o radial

· 40^o ulnar

Radial deviation

· distance between trapezium and radial styloid shortens

· scaphoid shifts to accommodate this

· provoked by impingement on radial styloid

· occurs in two ways

· sliding of scaphoid into lunate fossa

· flexion of scaphoid (distal pole of scaphoid shifts towards palm)

· transmitted to proximal row by scapholunate ligament

· causes sequental flexion of proximal row

· lunate then triquetral

Ulnar deviation

· distance between hamate and ulnar styloid shortens

· hamate migrates proximally to accommodate this

· causes triquetrum to move

· triquetrum migrates distally on hamate

· triquetrum dorsiflexes

· transmitted to lunate

· lunate extends

· movements also occur at scaphoid

· lunate slides into scaphoid fossa

· scaphoid passively extends

Functional motion

· motion for most activities

· arc of 45^o (10^o flexion and 35^o extension)

· maximum requirement is arc of 65^o

· most tasks requiring continuous arc of motion

· only require extension

· are performed from radial deviation/extension to neutral (eg. hammering)

Interaction of wrist and hand motion

· wrist positioned in opposite position of fingers to maximise functional length of digital tendons

· wrist extension is synergistic with finger flexion

· grip strength maximal with wrist extension

· wrist flexion is synergistic with finger extension

· wrist flexion causes fingers to open automatically

Concept of columns

Vertical columns

Kinetics

· main function is to transmit compressive loads from hand to forearm and vice versa

· load borne by

· distal radius 80%

· distal ulna via TFCC 20%

· most powerful wrist motor is FCU