Kinesiology of Wrist & Hand Flashcards
What is the most commonly fractured carpal bone?
Scaphoid
- Accounts for 60-70% of all carpal fractures
- Located in direct path of force transmission –> common cause of fracture: fall on fully supinated forearm w wrist extended & radially deviated
How are the carpal bones joined?
Proximal row (Scaphoid, lunate, triquetrum, pisiform): joined in relatively loose way
Distal row (Trapezium, trapezoid, capitate, hamate): bound tightly by strong ligaments –> forms a rigid & stable base for metacarpals
Which is the most unstable carpal bone?
Lunate
- Bc of shape & lack of muscular attachments & lack of strong ligamentous attachments to capitate
What ligament is attached to the tubercle of the trapezium?
Lateral side of transverse carpal ligament
(hook of hamate provides attachment for medial side of this ligament)
What are the 3 dominant ligaments in the palmar radiocarpal ligament?
- Radioscaphocapitate ligament
- Long radiolunate ligament
- Short radiolunate ligament
(derives from distal radius & attaches to palmar surfaces of carpal bones)
When is the palmar radiocarpal ligament maximally taut?
At full wrist extension
Which is the most active extensor muscle during light grasp?
Extensor carpi radialis brevis
- As force of grip inc. –> extensor carpi ulnaris & radialis longus
What happens with repetitive & forceful grasp?
Lateral epicondylagia (aka tennis elbow)
- Over-stress of proximal attachment site of wrist extensor muscles
When is the contact area of the radiocarpal joint the greatest?
Wrist is partially extended & slightly deviated in ulnar direction
What movement does the radiocarpal joint and midcarpal joint allow?
Allows wrist to flex & extend & move side to side (radial & ulnar deviation)
What are the proximal components of the radiocarpal joint?
Concave surfaces of radius & adjacent articular disc
What are the distal components of the radiocarpal joint?
Convex proximal surfaces of scaphoid & lunate
What is the midcarpal joint?
The articulation b/w proximal & distal rows of carpal bones
Arthrokinematics of ulnar/radial deviation
Synchronous convex-on-concave roll & slide at both radiocarpal & midcarpal (scaphoid, lunate, triquetrum) joints
The distal end of the radius is angled towards the ulnar/medial direction by how many degrees?
~25°
- Ulnar tilt allows wrist & hand to rotate further into ulnar deviation than into radial
What limits radial deviation?
Limited by bony impingement of lateral side of carpus against styloid process of radius
Why is there greater amount of wrist flexion than extension?
Distal articular surface of radius angled ~10° in palmar direction
Why kind of action has the path of least passive resistance?
Dart throwing action
- Maximises joint contact within major joints
- Limits rotation of scaphoid & lunate bones = dec. strain on scapholunate ligament
Where is the axis of rotation in the wrist?
Passes through capitate
- runs anterior-posteriorly for ulnar/radial deviation
- bc. capitate is firmly articulated w base of 3rd metacarpal –> rotation of capitate will direct osteokinematic path of whole hand
What happens to the scaphoid, lunate, triquetrum and capitate during ulnar deviation?
Scaphoid, lunate, triquetrum roll in ulnar direction & slide radially
Capitate rolls in ulnar direction & slides radially (slightly)
What are the additional arthrokinematics in radial/ulnar deviation?
Proximal row of carpal bones:
- Radial dev: flexes slightly
- Ulnar dev: extends slightly
What are the two inverted ‘V’s made up of?
4 ligaments
- Distal inverted V: formed by medial & lateral legs of palmar intercarpal ligament
- Proximal inverted V: formed by lunate attachments of palmar ulnocarpal & palmar radiocarpal ligaments
When in neutral position, are the four ligaments in the double-V system of ligaments taut or relaxed?
All 4 legs were under slight tension
