hand biomechanics Flashcards
hand complex
29 muscles
19 bones
19 articulation
transverse arches
proximal- capitate is keystone- more stable
distal-3rd MC head is center- more mobile
longitudinal arch
connects transverse arches
2 and 3 MCs form center
digits 2-4 CMC joints
plane synovial
1 dof flexion extension
5th cmc joint
saddle joint
2 dof
f e
abd add
mobility of cmc
increases radial to ulnar side
4-5th facilitate opposition
thumb cmc joint
diarthrodial saddle
2 dof
abd/add (cv on cc)
f/e (cc on cv)
closed- opposition
open- neutral
rom for thumb cmc
f/e 50 total
abd/add 40 total
MCP 2-5
diarthodial unicondylar
2dof (f/e and abd/add)
closed- full flexion
open- slight flexion
MCP rom
flexion- 90 at 2 mcp progresses to 110 at 5th mcp
extension- 30-40, 90 prom
abd- 20-30 in neutral, restricted in flexion
volar plate in mcp joints 2-5
increased congruency
stability
limits hyperextension
prevents flexor tendon pinching
mcp thumb
diarthrodial condyloid
1 dof f/e
ligament stability against abd add
rom mcp thumb
flexion 60
extension 0 to slight hyperextension
ip joints 1-5
bicondylar
proximal convex
distal concave
1 dof f/e
closed- full extension
open- slight flexion
rom ip joints
pip- flexion: 100-110 ext: 0
dip- flexion: 80 ext: 20
thumb ip- f: 80 ext: 20
volar plate ip joints
increased congruency
stability
limits hyperextension
prevents flexor tendon pinching
extensor digitorum
pass beneath ext retinatculum
each tendon has isolated bursa
only muscle capable of extending MCP
cannot extend pip or dip alone
isolated extrinsic extensors mcp ext, ip/dip flx
ip/dip ext require intrinsic muscle assistance
EI and EDM
independent control of 2 and 5
insert on ED tendons of 2 & 5
mcp joint extensor mechanism
ED pulls extensor hood proximally extending proximal phalanx
pip joint extensor mechanism
ED cant extend pip
intrinsics produce PIP extension through lateral bands
lumbrical contraction relaxes FDP and pulls lateral bands
dip joint extension mechanism
oblique retinaculum ligament is palmar to pip and tightens due to pip extension
ORL tightening pulls on terminal tendons to extend DIP
FDP flexor mechanism
FDP contraction initiated DIP flexion
lumbricals pulled proximally by FDP
lumbricals pull lateral bands volar to joint axis
DIP joint flexor mechanism
DIP flexion pulls terminal tendon and lateral bands distally
extensor hood flexor mechanism
extensor hood pulled distally relaxing central tendon for PIP flexion
what causes intrinsics to impart flexion at PiP
pull of FDP and absence of ED activity
power grip
flexion at all fingers
precision handling
finger- finger or finger- thumb skilled placement
pad to pad
tip to tip
pad to side
two jaw chuck- 2 digits
three jaw chuck- 3 digits (pencils, scissors)
functional hand position
wrist 20-30 extension
mcp- 35-45 flexion
pip/dip- 15-30 flexion
thumb cmc- 35-45 flexion
