hand biomechanics

Question 1

hand complex

Answer 1

29 muscles
19 bones
19 articulation

Question 2

transverse arches

Answer 2

proximal- capitate is keystone- more stable
distal-3rd MC head is center- more mobile

Question 3

longitudinal arch

Answer 3

connects transverse arches
2 and 3 MCs form center

Question 4

digits 2-4 CMC joints

Answer 4

plane synovial
1 dof flexion extension

Question 5

5th cmc joint

Answer 5

saddle joint
2 dof
f e
abd add

Question 6

mobility of cmc

Answer 6

increases radial to ulnar side

4-5th facilitate opposition

Question 7

thumb cmc joint

Answer 7

diarthrodial saddle
2 dof
abd/add (cv on cc)
f/e (cc on cv)

closed- opposition
open- neutral

Question 8

rom for thumb cmc

Answer 8

f/e 50 total
abd/add 40 total

Question 9

MCP 2-5

Answer 9

diarthodial unicondylar

2dof (f/e and abd/add)

closed- full flexion
open- slight flexion

Question 10

MCP rom

Answer 10

flexion- 90 at 2 mcp progresses to 110 at 5th mcp

extension- 30-40, 90 prom

abd- 20-30 in neutral, restricted in flexion

Question 11

volar plate in mcp joints 2-5

Answer 11

increased congruency
stability
limits hyperextension
prevents flexor tendon pinching

Question 12

mcp thumb

Answer 12

diarthrodial condyloid

1 dof f/e

ligament stability against abd add

Question 13

rom mcp thumb

Answer 13

flexion 60
extension 0 to slight hyperextension

Question 14

ip joints 1-5

Answer 14

bicondylar
proximal convex
distal concave

1 dof f/e
closed- full extension
open- slight flexion

Question 15

rom ip joints

Answer 15

pip- flexion: 100-110 ext: 0

dip- flexion: 80 ext: 20

thumb ip- f: 80 ext: 20

Question 16

volar plate ip joints

Answer 16

increased congruency
stability
limits hyperextension
prevents flexor tendon pinching

Question 17

extensor digitorum

Answer 17

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

Question 18

EI and EDM

Answer 18

independent control of 2 and 5

insert on ED tendons of 2 & 5

Question 19

mcp joint extensor mechanism

Answer 19

ED pulls extensor hood proximally extending proximal phalanx

Question 20

pip joint extensor mechanism

Answer 20

ED cant extend pip

intrinsics produce PIP extension through lateral bands

lumbrical contraction relaxes FDP and pulls lateral bands

Question 21

dip joint extension mechanism

Answer 21

oblique retinaculum ligament is palmar to pip and tightens due to pip extension

ORL tightening pulls on terminal tendons to extend DIP

Question 22

FDP flexor mechanism

Answer 22

FDP contraction initiated DIP flexion

lumbricals pulled proximally by FDP
lumbricals pull lateral bands volar to joint axis

Question 23

DIP joint flexor mechanism

Answer 23

DIP flexion pulls terminal tendon and lateral bands distally

Question 24

extensor hood flexor mechanism

Answer 24

extensor hood pulled distally relaxing central tendon for PIP flexion

Question 25

what causes intrinsics to impart flexion at PiP

Answer 25

pull of FDP and absence of ED activity

Question 26

power grip

Answer 26

flexion at all fingers

Question 27

precision handling

Answer 27

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)

Question 28

functional hand position

Answer 28

wrist 20-30 extension
mcp- 35-45 flexion
pip/dip- 15-30 flexion
thumb cmc- 35-45 flexion