28/29: Orthosis Fabrication - Mahoney Flashcards Preview

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Flashcards in 28/29: Orthosis Fabrication - Mahoney Deck (35)

characteristics of neutral position casting

–Non weight-bearing

–STJ neutral

–MTJ maximally pronated

–Ankle joint dorsiflexed to slight resistance


Technique to Neutral Casting

- Supine, grasp 4th and 5th toe sulcus

- Supine, thumb pressure beneath 4th and 5th metaheads

both maneuvers attempt to lock MTJ in pronated stable position


Review of Plastering Technique

30 x 5 inch splint is folded in half lengthwise.  A ½inch fold placed on length-wise edge for reinforcement.

Place splint around heel, 1/2 of length on eachside of foot at a height just below malleoli.  Mold lateral side first into arch and then medial side overlapping lateral half. Fold excess plaster on plantar of heel towards posterior aspect

The sides of the plaster are folded onto the plantar aspect of the foot, starting with lateral side first.  Any excess is folded under the sulcus of the toes.


What things do you need to check on a negative cast?

•5th toe impression should not be dorsiflexed or plantarflexed

•Lateral border should be straight or slightly abducted (it will be adducted in a patient with metatarsus adductus)

•Inside of heel should be concave from medial to lateral and symmetrical from side to side

•Skin lines should be present throughout

•Will sit on a table in varus with a forefoot valgus and in valgus with a forefoot varus

•Lateral arch should match lateral border of foot in neutral position


what is the casting technique for all functional devices and neutral shell orthoses?

neutral casting technique (NWB)



  1. allows foot to function around STJ position

  2. prevents abnormal or excessive compensation

  3. provides normal gait cycle

  4. improves or changes function


what is a neutral shell orthosis?

1.  does not have any forefoot or rearfoot posting

2.  reduces, but does not eliminate compensation, to allow for gradual posting

3.  gradual rearfoot posting can be used to gradually stretch out Achilles tendon


describe the rectus casting position

Non weightbearing

STJ neutral and MTJ maximally pronated

Dorsiflex ankle to slight resistance

Plantarflex 1st ray to level of the 5th metahead   by pressing down on the dorsum of the 1st   metahead or metabase or by dorsiflexing the   hallux


casting utilized in children less than 6 yo or pt who need increased arch support

RECTUS casting

- also used in UCBL inserts for max pronatory control

- preffered technique for prolabs for all orthotics (why? by plantarflexing the 1st metatarsal, you are everting the long axis of the MTJ (pronation) and making the forefoot stable in stance)


describe partial WB casting technique

  1. semi-weightbearing sitting position

  -can utilize plaster or foam box

  2. leg is 90° to the floor and the hip, knee, and ankle are at 90°

  3. patella is aligned with 2nd metatarsal

  4. STJ manipulated into neutral position


describe the foam box technique

- Maintain STJ in neutral with one hand and grasp lower leg with other hand

 - Lift foot and place on foam

 - Apply downward pressure to dorsal aspect of knee to drive heel into foam

 - Apply downward pressure to midfoot and then forefoot

- Foot is withdrawn from foam by provider


advantages of the foam box technique

- easy

- better judge STJ neutral position

- locks MTJ oblique axis via gravity against body weight


disadvantages: long axis of MTJ is supinated, decrease in FF valgus and increase in FF varus, first ray hypermobile due to supinated position of 1st ray


technique used for accomodative orthosis

foam box technique

- used to accommodate, pad or protect a foot deformity


scans negative cast or the foot directly

computerized imaging

–A physical positive cast can be milled out of a block of wood, or the orthosis can be milled directly out of a block of polypropylene from a “virtual” positive.


"milled orthoses" vs. normal heated plastic mold

•“Milled” orthoses are carved out of a solid block of plastic after the 3-D design has been generated on a computer following a scan of the negative cast

•Milled devices are more rigid because the plastic has not been heated and they have “mill lines” which are transverse corrugations in the orthosis. rearfoot post is also milled directly into plastic


most reliable casting when important to capture forefoot to rearfoot relationship

plaster casting  (NWB neutral impression)


When set on flat surface, the heel of the negative and positive cast will invert or evert the same number of degrees as the deformity.


If forefoot valgus/varus, the heel will ...

•If a forefoot valgus, the heel will invert

•If a forefoot varus, the heel will evert


intrinsic post

changes to the positive mold


•this example of forefoot valgus, the cast is balanced by hammering a nail into the cast’s 5th metahead region far enough so that the cast becomes level on a flat surface

Plaster is built up around the nail and smoothed out so that it is continuous with the arch of the mold


To add an intrinsic forefoot post for FF varus

elevate the 1st met head with a nail


platforms for forefoot varus/valgus

–For a forefoot varus, the platform will be thicker medially. 

–For a forefoot valgus, the platform will be thicker laterally.


standard functional device trimming

extends just proximal to the metatarsal heads distally, to the center of the first metatarsal medially and the center of the fifth metatarsal laterally


purpose of rearfoot post

acts as platform to stabilize the orthotic


0/0 post vs. 4/4 post

A 0/0 post is ground parallel to the front edge of the orthotic and is intended to keep the front edge flat in the shoe regardless of foot movement.

A 4/4 post is one in which the lateral aspect of the post is inverted 4 degrees to the front edge of the orthosis and there is 4 degrees of motion (eversion) allowed to bring the medial half of the post parallel to the front edge of the orthosis.

The first number is the amount of lateral grind on the post that holds the front edge inverted before forefoot loading. This is most often 4 degrees to accommodate the inverted position of the heel at heel contact.

The second number is the amount of motion the orthotic has during forefoot loading when the front edge comes down to the ground.


lateral skive provides a presribed amount of STJ pronation at ____________ phase.


- this allows STJ to function more normally and assist in shock absorption


The prescription for the rearfoot post is based on ...

height of STJ axis from the transverse plane


The lower the axis, the more inversion/eversion is available, the more pronated the foot, and the more motion control is necessary

normal = 4/4

low = 6/6

high = 2/2

0/0 = no inversion or motion


why do a medial heel skive?

to increase pronation control

- intrinsic modification to orthotic that creates an additional wedge that inverts the heel by increasing ground reactionforce medial to the STJ axis

- increased plastic at medial aspect of heel on orthotic

- more depth = more control


increasing the heel cup height helps to control motion of ...


- higher the heel cup height, the greater the control but also more difficult to fit into shoe


avg: 12-16 mm

high med: 14-18

high lat: 14-16

low med: 10-14

low lat: 8-12


why do a medial arch fill?

reduce irritation ofmedial arch form the orthotic

- plaster is added to the medial arch of the positive cast

However, if extra pronation control is desired, minimal arch fill will make the arch of the orthotic higher, helping to prevent pronation, especially if it is the result of increased frontal plane motion at the MTJ

EX Flatfoot: extra medial arch is added to the positive cast-when orthotic is formed to shape of cast, medial arch of the orthotic is lower than the foot’s medial arch which will reduce irritation of the orthotic on the arch

•Average medial arch: 4mm of fill

•High medial arch (cavus foot): 2 mm of fill

•Low medial arch (flat foot): 6 mm of fill


makes the orthotic wider to allow for soft-tissue spread

lateral expansion

•A functional orthotic is made from a negative cast taken in NWB position; thus, when foot bears weight, soft tissue is displaced laterally and medially

•Standard lateral expansion (3-5 mm): average soft tissue displacement

•Wide lateral expansion (5-10 mm): excessive soft tissue displacement


Top Cover Materials

  1. Neoprene/Spenco
    1. best anti-shear material
  2. Polyurethanes/PPT/Poron/Plastizote
    1. best memory gradient and vertical force resistance
  3. Visco elastomers/Sorbothane
    1. best shock attenuator, don't use
  4. Neoprene
  5. Leather
    1. hypoallergenic
  6. Naugahyde/Vinyl
    1. stretchable, tear resistant



added under topcover distal to edge of orthotic to support or accommodate metaheads

forefoot extension

- can have a valgus or varus wedge


why use a heel lift?

treat limb length inequality, ankle equinus, heel pain, scoliosis, calf or hamstring strain, hip pain

  • Maximum of ½ inch can be added for athletic shoes
  • three-eighth’s inch in men’s lace-ups
  • one-quarter inch in men’s loafers or women’s flats


sits under topcover just proximal to metaheads and off-loads metaheads

metatarsal pad

- ideal placement distance is 6.1 to 10.6 mm proximal to a line identifying the met head


pad that extends under the 1st metatarsal head and great toe to restrict 1st MPJ motion

morton's extension


Reverse Morton’s extension: pad that sits under the 2nd through 5th metaheads to accommodate 1st metahead for a lesion or allows plantarflexion of 1st metatarsal to improve 1st MPJ dorsiflexion


extra padding depressed into the body of the orthosis while the plastic is still hot to cushion prominent bones (navicular

"sweet spot"

can also pad around bones to 'float' them

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