Hand biomechanics

Question 1

What are the two arches of the hand?

Answer 1

1. Transverse- proximal (stable) and distal (mobile)

2. Longitudinal- connects transverse arches

Question 2

What kind of joints are CMC joints of the digits?

Answer 2

2-4th: plane synovial

5th: saddle
thumb: diarthrodial saddle

Question 3

What kind of joints are the MCP joints of the digits?

Answer 3

2-5: diarthordial unicondylar

thumb: diarthoridal condyloid

Question 4

What type of joint is the IP joint for digits 1-5?

Answer 4

bicondylar hinge joint

Question 5

What is the only muscle capable of extending MCP?

Answer 5

Extensor digitorum

lumbricals required to extend IP/DIP

Question 6

What muscle contraction initiates DIP flexion? aka flexor mechanism

Answer 6

FDP
DIP flexion pulls terminal tendon and lateral band distal
Extnesor hood pulled distal, relaxes for PIP flexion
Pull of FDP and absence of ED activity causes intrinsic to impart flexion at PIP

Question 7

What is the functional hand position?

Answer 7

wrist: 20 to 30 ext
MCP: 35-45 flex
PIP/DIP: 15-30 flex
thumb CMC: 35-45 flex

Question 8

What is the extensor mechanism?

Answer 8

MCP: ED pulls extensor hood proximally, extending phalanx ED can’t extend PIP
PIP: Lumbrical contraction relaxes FDP and pulls lateral bands
DIP: ORL is palmar to PIP and tightens due to PIP extension. ORL tightening pulls on terminal tendon to extend DIP