Biomechanics Wrist and Hand Flashcards
joints of the wrist
-purpose of the wrist
radiocarpal joint
midcarpal joint
assists the hands as they move in space
radiocarpal joint
-components
distal radius radioulnar articulate disc proximal row of carpal bones -scaphoid -lunate -triquetrum -I do not believe the pisiform articulates with the radius
midcarpal joint
-location
between proximal and distal rows of carpal bones
bones of the distal carpal row
trapezium
trapezoid
capitate
hamate
wrist osteokinematics
-motions
2 degrees of freedom
- sagittal plane motion (flexion/extension)
- frontal plane motion (radial and ulnar deviaiton)
radius angulation in relation to the ulna
-what is this called
angulated towards the ulna by 25 degrees
called ulnar tils
ulnar tilt
-consequence
allows wrist and hand to rotate further into ulnar deviation versus radial deviation
radial deviation is limited by…
styloid process
palmar tilt
- caused by…
- allows for…
distal articular surface of radius is angulated 10 degrees in the palmar direction
allows for greater wrist flexion than extension
scaphoid
-which row is it in, anatomically and functionally
spans both proximal and distal row, both anatomically and functionally, due to its elongated shape
pisiform
- type of bone
- location
- function
sesamoid bone that sits on top of the triquetrum
mechanically enhances the pull of the flexor carpi ulnaris by giving it a longer moment arm
promixal carpal row
- which muscles attach to these
- mobility compared to distal row
- overall function
no muscles attach there
very mobile compared to distal row
servse as a mechanical link between the forearm and hand
when the link created by the proximal carpal row is compromised…
you have a zigzag collapse
ligaments are typically damaged
result is carpal instability
scaphoid convex poles
-articulate with…
proximal pole
-articulates with scaphoid facet of radius
distal pole
-articulates with trapezium and trapezoid
distal carpal row
- level of mobility
- functions as a…
very stable
functions as a relatively immobile transverse unit
radiocarpal joint
-type of joint
condyloid joint
how does load sharing occur between the radius and ulna
-why is it important
ulna has no articulation with carpals
load transmitted to ulna via interosseus membrane
Radioulnar articular disc (TFC)
- what is it?
- function
biconcave fibrocartilaginous disc
transfers compressive forces from the hand to the forearm
how is the convex head of the ulna held to the distal radioulnar joint
by the proximal side of the TFC
what is the function of the distal surface of the TFC
holds the convex lunate and triquetrum of the RC joint
central portion of TFC vascularity
avascuar
-poor healing capabilities
TFCC function
primary stabilizer of distal radioulnar joint
reinforces ulnar side of wrist
forms concavity in RC joint
transfers force from hand to forearm
binds ulna and radius together distally while allowing radius to rotate over fixed ulna for pronation and supination
midcarpal joint
-functional compartments
medial and lateral
midcarpal joint medial compartment
- articulations
- arthrokinematic rule
articulations
-convex head of capitate and apex of hamate articulate with the concave depression in the scaphoid, lunate, and triquetrum
follows convex on concave rule
midcarpal joint lateral compartment
- articulations
- arthrokinematic rule
convex distal pole of the scaphoid articulates with the concave trapezium and trapezoid
concave on convex rules
arthrokinematics during…
-ulnar deviation
medial (ulnar) roll and lateral (radial) slide of the distal on proximal bones
how many bones in the hand?
how many separate joints distal to the carpal bones?
19 bones
19 joints
each metacarpal is comprised of…
base
shaft
head
1st CMC
-articulation
1st met
trapezium
2nd CMC
- primary articulation
- secondary articulation
2nd met primary -trapezoid secondary -capatate -trapezium
3rd CMC
-articulation
3rd met
capitate
4th CMC
- primary articulation
- secondary articulation
4th met primary -hamate secondary -capitate
5th CMC
-articulation
5th met
hamate
CMC joints 2-4 degrees of freedom
-motions allowed
1 degree
flexion/extension
CMC joints 1 and 5
- type of joint
- degrees of freedom
- motions allowed
saddle joints 2 df flexion/extension abduction/adduction opposition
CMC joints
- which are stable
- which are mobile
stable
-2, 3
mobile
-1, 4, 5
1st CMC
- orientation compared to other CMCs
- purpose
internally rotated 90 degrees relative to other digits
allows full opposition to contact the other digits
-provides critical link for prehensile activities
1st CMC saddle arthrokinematics
trapezium -concave in sagittal plane -convex in frontal plane 1st metacarpal -convex in sagittal plane -concave in frontal plane
MCP arthrokinematics
-type of joint
distal end of met has convex head articulating with concave base of proximal phalanx condyloid joint -2 df MCP of thumb has 1df all MCP joints follow concave on convex
IP joints
- type of joint
- df
- arthrokinematic rule
hinge joint
1 df
concave on convex rule
arches of the hand
-names
proximal transverse arch
distal transverse arch
longitudinal arch
longitudinal arch
- where is it rigid
- where is it mobile
- follows the shape of…
- what is considered the stable keystone of the arch
rigid proximally
mobile distally
follows shape of 2nd and 3rd rays
2nd and 3rd MCP considered stable keystone
proximal transverse arch
- location
- how stable
- keystone structure
at level of carpal bones
very rigid
capitate is keystone
distal transverse arch
- location
- how stable
- keystone structure
located at level of metacarpal heads
very mobile
MCP joints are keystone of arch
function of arches of hand -what maintains their shape
allow us to grasp, hold, release, and manipulate objects of varying shapes and sizes
shape maintained by intrinsic muscles
primary passive structures of the hand
volar (palmar) plates
flexor tendon pulley system
extensor mechanism of the fingers
volar plates
- what are they
- function
what -fibrocartilage plates located on the volar surface of MCP, PIP, and DIP joints function -reinforce anterior joint capsules -prevent impingement of flexor tendons during flexion -limit hyperextension at these joints
damage to volar plate
- name of deformity
- description of deformity
Swan Neck Deformity
- DIP in flexion
- PIP in hyperextension
Swan Neck deformity etiology
can be caused by synovitis of the flexor tendon sheath
increased flexion pull on the MP joint causes an imbalance to the extensor central slip through the long extensor tendons and the intrinsic muscles
stretch to the volar plate at the PIP causes hyperextension of the PIP
lateral intrinsic tendons shift dorsally and reciprocal flexion occurs at the DIP
flexor tendon pulley system
-components
2 digital flexor tendons -FDS -FDP -tendons lie in their synovial sheaths which are secured against the phalanges by a fibrous sheath 5 annular pulleys (A1-A5) 3 cruciform pulleys (C1-C3)
flexor tendon pulley system
-function
maintain efficient and smooth gliding of the flexor tendons while maintaining their mechanical advantage
damage to flexor tendon pulley system
- names
- how it happens
bowstring phenomenon -rupture a pulley (A1-5) trigger finger -nodule of tendon becomes inflamed -nodule gets trapped behind tendon sheath, finger becomes stuck in flexed position
extensor mechanism of fingers
-components
extensor digitorum tendon (backbone)
- split into 3 sections
- -central (dorsal) band
- -2 lateral bands
extensor mechanism of fingers
- function
- how does it work
coordinates movements between PIP and DIP joints
mechanism has multiple attachments along the phalanges allowing transfer of extensor forces distally through the entire digit
dorsal hood transverse fibers
- location
- why is it necessary for function of the extensor mechanism
at proximal end of extensor mechanism at the MCP joints
transverse fibers run perpendicular to the ED tendon, attaching to the volar plate of the proximal phalanx to create a sling that assists the ED tendon with MCP extension
dorsal oblique fibers
- contains which muscles
- location
- function
contains muscle fibers of the lumbricals and interossei
runs distally to attach into lateral band of extensor mechanism
aids extensor mechanism in extension of PIP and DIP joints
damage to extensor mechanism
- name of deformity
- what happens
- description of deformity
Boutonniere Deformity
tear in central slip
PIP joint in flexion
DIP in hyperextension
function of the wrist in relation to hand motion
controls length tension relationship in the hand
balance and control of fine motor adjustments
function of the wrist for grasp and prehension
- maximum grip strength in _____
- least grip strength in _____
maximum grip strength in 20-35 extension
minimum grip strength in full flexion
how much wrist motion is required for common ADL’s
- which motions are most important
- what are the coupled motions
54 flexion 60 extension 17 radial deviation 40 ulnar deviation extension and UD most important combined motions -extension with RD -flexion with UD
wrist ligament functions
-are palmar or dorsal ligaments stronger
restrict joint motion and oppose joint surfaces
can cause bone movement (displacement)
maintain structure
facilitate precise loads
transmit loads to proximal and distal segments
palmar ligaments stronger
extrinsic wrist ligaments
-characterisitics
more likely to fail with injury than intrinsic good healing (vascularity from surrounding tissue)
what are the extrinsic wrist ligaments
dorsal radiocarpal ligament
radial collateral ligament
palmar radiocarpal ligament
dorsal radiocarpal ligament
-function
reinforces posterior radiocarpal joint
guides arthrokinematics of proximal row
prevents anterior dislocation of the unstable lunate
radial collateral ligament
-function
provides little lateral stability
palmar radiocarpal ligament
- strength compared to dorsal RC ligament
- when does it provide support
stronger and thicker than dorsal RC lig passive tension (even in neutral) maximally taut in full extension
TFCC vascularity
80% avascular
intrinsic wrist ligaments
-characteristics
stronger than extrinsic ligaments
lie within the synovial lining
rely on synovial fluid for nutrition
slow healing capacity (poorly vascularized)
intrinsic wrist ligaments
-names
short ligaments intermediate ligaments (don't need to know names) -lunotriquetral -scapholunate -scaphotrapezial long ligaments -palmar intercarpal "V" ligament dorsal intercarpal ligament
short ligaments (wrist) -function
connect bones of distal row
stabilize and unite distal row
allows distal row to function as a single mechanical unit
palmar intercarpal “V” ligament
- function
- what do the “legs” connect
guides arthrokinematics lateral leg -palmar capitate to scaphoid medial leg -palmar capitate to triquetrum
dorsal intercarpal ligament
- function
- connects…
provides transverse stability
connects trapezium, scaphoid, lunate, and triquetrum
retinaculum
- what are they?
- function
thickenings of fascia
can form a tunnel-like effect to keep tendons in correct position
prevents bowing out during muscle activation
carpal tunnel and transverse carpal ligament (TCL)
- what is it?
- function
TCL makes a tunnel with carpal bones (carpal tunnel)
passageway for median nerve and 9 extrinsic flexor muscles of the digits
restrains ligaments from bowstringing
thumb opposition
-phases and description of each
phase 1
-abduction
phase 2
-flexion, medial rotation (spin) of metacarpal
what provides the passive tension in the MCP’s to stabilize the joint for grasping
dorsal capsule
skier’s thumb
- what is it
- in what position does it occur
UCL tear
occurs at 45 degrees abduction, 30 degrees flexion
lumbricals of hand
-function
flex MCP joint
extend IP joint
interossei
-functions
dorsal
-abduct digits and assist lumbricals
palmar
-adduct digits and assist lumbricals
names of functional positions of the hand
extrinsic plus
intrinsic plus
extrinsic plus hand position
- what is the position
- what combined muscle activations create this position
MCP extension, PIP and DIP flexion
muscle activation
-simultaneous contraction of the extrinsic finger muscles (ED, FDS, FDP)
intrinsic plus hand position
- what is the position
- what combined muscle activation create this position
MCP joint flexion, PIP and DIP extension
muscle activation
-simultaneous contraction of the intrinsic finger muscles (lumbricals and interossei)
names of 5 types of prehension
power grip precision grip power (key) pinch precision pinch hook grip - laundry grip
power grip
- purpose
- shape
- muscles
stability, large force but low precision spherical or cylindrical shape muscles -finger flexors -intrinsic muscles -thumb abductor/flexor -wrist extensors to stabilize
precision grip
- purpose
- shape
- use of fingers
control, precision
fingers partially flexed, thumb partially abducted
selectively use fingers and/or thumb to improve security and modify force
alter distal transverse arch to fit objects
power (key) pinch
- when is it used
- where are objects held
- muscles
large forces needed stabilize object between thumb and lateral border of index finger muscles -adductor pollicis -1st dorsal interossei
precision pinch
- purpose
- where are objects held
fine control
objects held between thumb and index finger
tip-to-tip and pulp-to-pulp
hook grip - laundry grip
- what fingers involved
- shape
- muscles
does not involve thumb
partially flexed PIPs/DIPs of fingers
force primarily from FDP
what strucutures are responsible for the following conditions
- Boutonniere deformity
- swan neck deformity
- De Quervain’s
Boutonniere -extensor hood Swan neck -volar plate De Quervain's -extensor pollicis brevis -abductor pollicis longus
most commonly
- dislocated carpal
- fractured carpal
dislocation
-lunate
fracture
-scaphoid
distal radius fractures
- most common MOI
- results in…
FOOSH mechanism
results in displacement of the distal aspect of the radius
ulnar neuropathy
- what is damaged
- -this affects…
- result
deep motor branch affected -hypothenar muscles -medial 2 lumbricals -palmar interossei -dorsal interossei -adductor pollicis results in atrophy
