Foot orthoses: design and manufacture Flashcards
define foot orthoses
an in-shoe medical device which is designed to alter the magnitudes and temporal patterns of the reaction forces on the plantar aspect of the foot in order to allow more normal foot and lower extremity function and to decrease pathalogical loading forces on the structural componenets of the foot and lower extremities during WB activities
what does a foot orthosis do
change the location and temporal patterns of forces act on the underside of teh foot
changes to stressess acting in tissues
changes to joint moments
changes to kinematic, kinetic anf temprospatial parameters of gait and stanfce
Types of foot orthoses
custom, customised, prefab, off the shelf
traditional orthosis manufacture
negatic cast
positive cast
vacuum form shell
post and finish orthosis
negatie case
non WB plaster cast - suspension or prone
WB or semi-WB foam impression
Difference between WB and non WB
WB = lower arch, wider and longer
nonWB
practicioner has control over foot
accomodation for ST deformation required during positive case modification
can be physically demanding
WB or patial WB
lower arch, wider, longer
captures the foot more representative of stance
cast pour angle
neutral: calc bisection is vertical relative to FF
inverted: calc bisection is inverted relative to FF (increases medial arch high, increase STJ supination)
EvertedL cacl is everted relative to FF (decreases medial arch height
Modifying the positive cast
FF platform
lateral expansion
medial expansion
FF platform - balanacing
Nails are hammered into the FF at MPJ1 and MPJ5
location of nails give landmarks used to control: orthotic shell lenght and forefoot width
Lateral expansion
plaster added to lateral border of postive - allows for expansion of ST and accomodates thicker covering materials
Pressing (vacuum forming)
with completed +ve cast - shell material is vacuum formed to the shape
materials = flexible to rigid
chosen material heated in oven and then pressed on the positive cast
shaping
following pressing material is removed to obtain the shape of the eventual orthosis
Extrinsic RF post
frontal plane alignment of underside relative to the calc bisection
heel pitch
drop of RF relative to underside of stabiliser
important for footwear fit
Heel raise
thickness of material between underside of heel and underside of stabiliser
Covering used for:
change shear forces at skin
protect foot from minor imperfections in shell
enhance durability of eva devices and padding
Strucuterd light 3D scanning
a pattern of light is projected upon the object
laser scanner
uses laser to capture depth and shape
contact digitiser
use pins to capture the data
are 3D scanners better than casting
accuracy and error
timingL capture time and processing time, clinical workflow, having and person lay still
cost: equipment, softwar, shipping
do you need it to be portable
Assessing a scan
are there holes in teh scan
can you see the RF bisection
FF to RF alignment
have you capture the height of the MLA
toe alignment
does it match the foot
Rigid orthotic shell material
materials that deform through bending
SHANK independent - dont rely on the shoe
Semi-rigid to felxible orthotic shell materials
materials that deform through compression
SHANK dependent - rely on the orthotic
Stiffness
property of base material
Hardness
shoreco
compresion set
permanent deformation remaining after removal of a force
resilience
ability of a material to absorb energy when it is deformed and release that energy upon unloading
tensile strenght
the resistance of a material to breaking under tension
Polypropylene
Used to make rigid orthoic shells - easily moulded with het
advantage: thin compared to EVA, can choose thickness, tough and flexible
DIsadvantages: limited adjustability, 3/4 lenght
Carbon fibre
used to make rigid orthotic shells
Pros: musch lighter and thingers for same rigitiy
cons: more expensive, less adjustable
EVA
rubber like
advantagesL easier to modify, full lenght
disadvantages: bulkier orthotic, hard to fit to some sheos
poron
used for cushioning and pressure reduction
cons: tear easily with shear load
can bottom out
PLastazote
is a closed cell cross-linked polyethylene foam
