Extrinsic Muscles of the Fingers Flashcards
extrinsic v. intrinsic musculature (ex)
extrinsic musculature: originates in the forearm and inserts in the hand
O is outside of the hand, I is in the hand
extrinsic v. intrinsic musculature (in)
the muscle origin and insertion is entirely w/in the hand
O/I are completely in the hand
extrinsic finger flexors
flexor digitorum superficialis (FDS)
flexor digitorum profundus (FDP)
FDS can flex the…
MCP and PIP joints
FDP can flex the…
MCP, PIP, DIP
what force must counter balance the finger flexors
wrist extensors
preventing active insufficiency
what is efficient finger flexion dependent on
an intact gliding mechanism
flexor mechanism
what consists the flexor mechanism
retinaculae
ligaments
bursae
tendon sheaths
hold the tendons to the hand and allow friction free movement
what happens when there is an interruption in the flexor mechanism
lead to decrease in FDS or FDP functioning
deformity
affect ability to function
what else does the flexor mechanism allow
not only smooth active movements of the tendons
also permits smooth passive excursion during finger flexion
which muscle is more active during flexion
FDP
can cause full hand closure w/o active assistance from other muscles
is the grip caused only by the FDP sufficient?
no the grasp is ineffective
passive help from intrinsics in necessary
when does FDS function alone
in finger flexion only when flexion of the DIP is not required
no DIP flexion –> no FDP
when DIP joint flexion is required
we use flexor digitorum profundus and superficialis acts as a reserve muscle
when else will FDS be active
when we need increased finger flexion force or when we have simultaneous wrist and finger flexion
finger extensors
extensor digitorum
extensor indicis
extensor digiti minimi
where does ED insert
into each finger on the middle phalanx by a central tendon
on the distal phalanx by a terminal tendon
which muscle is the only muscle that can extend the MCP joints
extensor digitorum
the extensor mechanism (1)
Ed tendons will pass beneath the extensor retinaculum
protected by a synovial sheath
extensor mechanism (2)
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
extensor mechanism (3)
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
where else does the extensor hood receive fibers from
interossei and lumbricals
at MCP joint finger extensors
an active contraction of ED creates tension in the hood
pulls the hood proximally
extends the proximal phalanx
extending the MCP joints
(@PIP joint) can the ED produce finger extension
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
(@PIP joint) what active contraction is needed for finger extension
active contraction of the interosseous or lumbrical muscle is capable of extending the PIP
need intrinsic muscles to assist
what deformity will occur if there is no assistance from the intrinsics (@PIP extension)
claw deformity
extension of PIP joint is accompanied by
simultaneous extension of the DIP
(@DIP) DIP and PIP are linked by
passive and active forces
DIP and PIP extension are interdependent
one moves, the other moves
how else are the DIP and PIP linked
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
simultaneous MCP, PIP and DIP extension
requires contraction of ED, EI, EDM, lumbricals and interossei
flexion mechanism allows for muscles to glide into and back of out relaxed position
