28/29: Orthosis Fabrication - Mahoney

Question 1

characteristics of neutral position casting

Answer 1

–Non weight-bearing

–STJ neutral

–MTJ maximally pronated

–Ankle joint dorsiflexed to slight resistance

Question 2

Technique to Neutral Casting

Answer 2

• 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

Question 3

Review of Plastering Technique

Answer 3

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.

Question 4

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

Answer 4

• 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

Question 5

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

Answer 5

neutral casting technique (NWB)

Question 6

FUNCTIONAL orthosis

Answer 6

1. allows foot to function around STJ position
2. prevents abnormal or excessive compensation
3. provides normal gait cycle
4. improves or changes function

Question 7

what is a neutral shell orthosis?

Answer 7

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

Question 8

describe the rectus casting position

Answer 8

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

Question 9

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

Answer 9

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)

Question 10

describe partial WB casting technique

Answer 10

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

Question 11

describe the foam box technique

Answer 11

• 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

Question 12

advantages of the foam box technique

Answer 12

• 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

Question 13

technique used for accomodative orthosis

Answer 13

foam box technique

• used to accommodate, pad or protect a foot deformity

Question 14

scans negative cast or the foot directly

Answer 14

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.

Question 15

“milled orthoses” vs. normal heated plastic mold

Answer 15

• “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

Question 16

most reliable casting when important to capture forefoot to rearfoot relationship

Answer 16

plaster casting (NWB neutral impression)

Question 17

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 …

Answer 17

• If a forefoot valgus, the heel will invert
• If a forefoot varus, the heel will evert

Question 18

intrinsic post

Answer 18

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

Question 19

To add an intrinsic forefoot post for FF varus

Answer 19

elevate the 1st met head with a nail

Question 20

platforms for forefoot varus/valgus

Answer 20

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

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

Question 21

standard functional device trimming

Answer 21

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

Question 22

purpose of rearfoot post

Answer 22

acts as platform to stabilize the orthotic

Question 23

0/0 post vs. 4/4 post

Answer 23

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.

Question 24

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

Answer 24

contact

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

Question 25

The prescription for the rearfoot post is based on …

Answer 25

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

Question 26

why do a medial heel skive?

Answer 26

• 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

Question 27

increasing the heel cup height helps to control motion of …

Answer 27

STJ

• 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

Question 28

why do a medial arch fill?

Answer 28

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

Question 29

makes the orthotic wider to allow for soft-tissue spread

Answer 29

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

Question 30

Top Cover Materials

Answer 30

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

Question 31

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

Answer 31

forefoot extension

• can have a valgus or varus wedge

Question 32

why use a heel lift?

Answer 32

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

Question 33

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

Answer 33

metatarsal pad

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

Question 34

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

Answer 34

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

Question 35

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

Answer 35

“sweet spot”

can also pad around bones to ‘float’ them