Extrinsic Muscles of the Fingers

Question 1

extrinsic v. intrinsic musculature (ex)

Answer 1

extrinsic musculature: originates in the forearm and inserts in the hand

O is outside of the hand, I is in the hand

Question 2

extrinsic v. intrinsic musculature (in)

Answer 2

the muscle origin and insertion is entirely w/in the hand

O/I are completely in the hand

Question 3

extrinsic finger flexors

Answer 3

flexor digitorum superficialis (FDS)

flexor digitorum profundus (FDP)

Question 4

FDS can flex the…

Answer 4

MCP and PIP joints

Question 5

FDP can flex the…

Answer 5

MCP, PIP, DIP

Question 6

what force must counter balance the finger flexors

Answer 6

wrist extensors

preventing active insufficiency

Question 7

what is efficient finger flexion dependent on

Answer 7

an intact gliding mechanism

flexor mechanism

Question 8

what consists the flexor mechanism

Answer 8

retinaculae

ligaments

bursae

tendon sheaths

hold the tendons to the hand and allow friction free movement

Question 9

what happens when there is an interruption in the flexor mechanism

Answer 9

lead to decrease in FDS or FDP functioning

deformity

affect ability to function

Question 10

what else does the flexor mechanism allow

Answer 10

not only smooth active movements of the tendons

also permits smooth passive excursion during finger flexion

Question 11

which muscle is more active during flexion

Answer 11

FDP

can cause full hand closure w/o active assistance from other muscles

Question 12

is the grip caused only by the FDP sufficient?

Answer 12

no the grasp is ineffective

passive help from intrinsics in necessary

Question 13

when does FDS function alone

Answer 13

in finger flexion only when flexion of the DIP is not required

no DIP flexion –> no FDP

Question 14

when DIP joint flexion is required

Answer 14

we use flexor digitorum profundus and superficialis acts as a reserve muscle

Question 15

when else will FDS be active

Answer 15

when we need increased finger flexion force or when we have simultaneous wrist and finger flexion

Question 16

finger extensors

Answer 16

extensor digitorum

extensor indicis

extensor digiti minimi

Question 17

where does ED insert

Answer 17

into each finger on the middle phalanx by a central tendon

on the distal phalanx by a terminal tendon

Question 18

which muscle is the only muscle that can extend the MCP joints

Answer 18

extensor digitorum

Question 19

the extensor mechanism (1)

Answer 19

Ed tendons will pass beneath the extensor retinaculum

protected by a synovial sheath

Question 20

extensor mechanism (2)

Answer 20

just distal to the MCP joint

the ED tendon will flatten into an aponeurotic hood

just proximal to the head of the proximal phalanx –> the hood splits into 3 segments

Question 21

extensor mechanism (3)

Answer 21

hood splits into a central band (which inserts at base of middle phalanx)

2 lateral bands (pass either side of central tendon)

• cross the proximal joint, reunite and insert as one terminal tendon on the distal phalange

Question 22

where else does the extensor hood receive fibers from

Answer 22

interossei and lumbricals

Question 23

at MCP joint finger extensors

Answer 23

an active contraction of ED creates tension in the hood

pulls the hood proximally

extends the proximal phalanx

extending the MCP joints

Question 24

(@PIP joint) can the ED produce finger extension

Answer 24

an isolated ED contraction cannot produce enough torque to overcome passive resistance of finger flexors –> cannot produce PIP extension

Ed cannot overcome passive amount of tension in the finger flexors

Question 25

(@PIP joint) what active contraction is needed for finger extension

Answer 25

active contraction of the interosseous or lumbrical muscle is capable of extending the PIP

need intrinsic muscles to assist

Question 26

what deformity will occur if there is no assistance from the intrinsics (@PIP extension)

Answer 26

claw deformity

Question 27

extension of PIP joint is accompanied by

Answer 27

simultaneous extension of the DIP

Question 28

(@DIP) DIP and PIP are linked by

Answer 28

passive and active forces

DIP and PIP extension are interdependent

one moves, the other moves

Question 29

how else are the DIP and PIP linked

Answer 29

1) active or passive flexion of the DIP will normally be accompanied by flexion of the PIP

2) full flexion of the PIP (active or passive) will prevent the DIP from being actively extended

Question 30

simultaneous MCP, PIP and DIP extension

Answer 30

requires contraction of ED, EI, EDM, lumbricals and interossei

flexion mechanism allows for muscles to glide into and back of out relaxed position