Wrist biomechanics

Question 1

What type of joint is the wrist? ROM? capsular pattern?

Answer 1

biaxial condyloid (flex/ext, RD/UD)
65 flex, 60 ext.
15 RD, 20 UD
flexion=extension

Question 2

What is the axial load sharing in the Radiocarpal joint?

Answer 2

80% goes to scaphoid/lunate

20% goes to TFCC

Question 3

If the ulnar styloid is too proximal or distal, what does this cause?

Answer 3

proximal: negative variance. Keinbock’s disease
distal: positive variance. TFCC

Question 4

What two intrinsic ligaments help to keep forces in the scaphoid and lunate in check?

Answer 4

scapholunate interosseous

lunotriquetral interosseous

Question 5

What forces do the scaphoid and lunate create?

Answer 5

scaphoid: flexion moment or palmar force; fractured in FOOSH
lunate: extension moment or dorsal force; dislocated in FOOSH

Question 6

What is the foundation of the transverse and longitudinal arches of the hand (gripping)?

Answer 6

Union of the distal carpals and metacarpals (fixed unit)

Question 7

What is the difference between extrinsic and intrinsic ligaments?

Answer 7

Intrinsic is stronger but slower healing. Relies on other things for nutrients

Question 8

What is a scapholunate disruption?

Answer 8

lunate tips dorsally due to connection to triquetrium

Question 9

What is a lunotriquetral disruption?

Answer 9

lunate dips palmarly due to connection to scaphoid

Question 10

The muscles of the wrist complex are stabilized by what? What are these muscles’ role?

Answer 10

extensor retinaculum and transverse carpal ligament
role is to be a stable base for hand and optimize length-tension relationship.
(Flex>Ext, RD>UD)