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Biomechanics > 8) Casting Techniques and Orthotic Fabrication > Flashcards

8) Casting Techniques and Orthotic Fabrication Flashcards

1
Q

Impression (negative) casting technique

A
  • Neutral suspension technique
  • Prone technique
  • Vacuum technique
  • Semi - weight bearing technique
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2
Q

Neutral suspension technique materials

A
  • Plaster or STS casting sock
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3
Q

Prone technique materials

A
  • Plaster or STS casting sock
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4
Q

Vacuum technique materials

A
  • Plaster or STS casting sock
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5
Q

Semi - weight bearing technique materials

A
  • Plaster or foam
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6
Q

Why impression casting?

A
  • Necessary for the fabrication of an orthotic device
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7
Q

Orthoses

A
  • Prescription medical devices which alter lower extremity alignment and function
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8
Q

Basic types of orthoses

A
  • Functional

- Accommodative

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9
Q

Functional orthoses support/balance

A
  • Existing forefoot deformity

- Eliminates the need for rearfoot compensation

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10
Q

Functional orthoses promote/limit

A
  • Subtalar joint motion

- Stabilizes (“locks”) the midtarsal joint

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11
Q

Functional orthoses design

A
  • Rearfoot posted
  • Rigid / semi-rigid materials (traditionally)
  • Derived from a NWB neutral cast
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12
Q

Functional orthoses indications

A
  • Forefoot deformity
  • Rearfoot deformity
  • Postural instability
  • Abnormal transverse plane leg rotation
  • Subtalar joint hypermobility
  • Limitation of subtalar joint motion
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13
Q

Accommodative orthoses

A
  • Redistribution of plantar pressure
  • Provides arch support
  • Promotes / limits subtalar joint motion to some degree
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14
Q

Accommodative orthoses design

A
  • Flexible materials generally utilized

- Derived form a NWB or semi-weight bearing casting technique

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15
Q

Accommodative orthoses indications

A
  • Neuropathy
  • Painful plantar lesions
  • Increased shock absorption
  • Subtalar joint hypermobility
  • Postural instability
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16
Q

Neutral suspension casting technique

A
  • Most commonly utilized method
  • Most technically difficult method
  • Excellent visualization of the subtalar joint neutral position
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17
Q

Neutral suspension technique limb and practitioner positioning

A
  • Patient supine with leg extended
  • Knee maintained in the frontal plane
  • Practitioner may be seated or standing
  • Thumb placed in sulcus of 4th and 5th digits
  • Subtalar joint palpated and neutral position identified
  • Forefoot loaded (midtarsal joint locked)
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18
Q

Neutral suspension casting STJ positioning

A
  • Foot must be placed in “neutral” position
  • STJ in neutral ~1/3 eversion:2/3 inversion
  • Look at concavity/convexity over sinus tarsi
  • Palpate dells of tarsal canal
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19
Q

Neutral suspension casting MTJ, OMTJ, LMTJ positioning

A
  • MTJ locked
  • OMTJ maximally pronated (abduction, dorsiflexion)
  • LMTJ maximally pronated (supinatus)
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20
Q

Neutral suspension casting patient positioning

A
  • Relaxed, comfortable and encouraged not to help
  • Casted leg internally rotated
  • Knees flexed
  • Foot in neutral position
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21
Q

Neutral suspension casting plaster application

A
  • Two piece method
  • Tuck excess in toe sulcus medially
  • Do not allow arch to bowstring
  • Capture curvature below fibular malleolus
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22
Q

Prone technique

A
  • Very common
  • Less difficult than neutral suspension
  • Excellent visualization of STJ neutral
  • Excellent when the patient is large
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23
Q

Evaluation of the negative: lateral border

A
  • Should be straight

Exceptions:

  • Metatarsus adductus
  • Large muscle belly
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24
Q

Evaluation of the negative: 5th toe position

A
  • Indicates position of the OMTJ
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25
Q

Evaluation of the negative: 1st ray

A
  • Contour of dell
  • Skin lines along the declination of the first metatarsal
  • No transverse lines proximal to head
  • Indicates position of the LMTJ
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26
Q

Evaluation of the negative: contour of the heel pad

A
  • Trisect the heel
  • Middle 1/3 should be flat
  • Medial 2/3 curved (supination of rearfoot)
  • Evaluates the STJ position
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27
Q

Semi-weight bearing technique

A
  • Commonly utilized
  • Technically easy
  • Difficult to maintain STJ neutral
  • Indicated primarily when accommodation is desired
28
Q

Semi-weight bearing technique is indicated primarily when

A
  • Accommodation is desired

- Biofoam

29
Q

Vacuum technique

A
  • Uncommon method
  • Minimal difficulty, but special equipment required
  • Excellent visualization of STJ neutral
  • Excellent when tight or specialized shoes are to be worn (skates, ski boots, high heels, etc.)
30
Q

Considerations when pouring the positive

A

Calcaneal bisection
- Dell below lateral malleolus)

Data from bioeval

  • What is NCSP?
  • Does foot pronate to perpendicular?
  • Is it maximally pronated at ?
31
Q

Pouring the positive

A
  • Separating medium
  • Wedge forefoot to place rearfoot in desired position (can invert up to 4°)
  • Apply dye to plaster
  • May reinforce with tongue depressor
32
Q

Pouring the negative: vertical

A
  • When STJ motion is adequate and the calcaneus can evert beyond perpendicular
33
Q

Pouring the negative: inverted

A
  • When STJ motion is limited and the calcaneus cannot evert to perpendicular
34
Q

Pouring the negative: everted

A
  • When STJ is in a fixed everted position or cannot invert to perpendicular
35
Q

Preparing for balancing

A
  • Negative is removed
  • “Menesci” rasped away
  • “Fabricot” is used to smooth the surface
  • Dye in positive prevents removal of excessive plaster
36
Q

Concept of balancing

A
  • Provide MTJ control
  • Custom made walking surface
  • Eliminate compensation which results in abnormal foot mechanics
37
Q

Why intrinsically balance?

A
  • To support the forefoot deformity and prevent midstance STJ compensation
  • Brings the “ground up to the foot”
  • Enables better fit in shoe gear
38
Q

Extrinsic balancing

A
  • No balancing of positive cast

- Forefoot balance platform added to orthotic plate

39
Q

Extrinsic vs. intrinsic balancing

A
  • Best shoe fit = intrinsic
  • Fewest problems = intrinsic
  • Best support of forefoot deformity = extrinsic
40
Q

When rigid forefoot valgus or varus exists, use

A
  • Extrinsic post
41
Q

When the forefoot deformity is > 5 degrees, use

A
  • A combination of balancing techniques
42
Q

Steps in preparing the positive

A
  • Forefoot balance platform (supports the forefoot deformity)
  • Medial expansion
    (allows for expansion with normal midstance pronation)
  • Lateral expansion
    (fat pad displacement)
43
Q

Forefoot balance platform purpose

A
  • To support the forefoot deformity
  • Identify forefoot contact points
  • Reference levels for balancing
  • Size of platform must be proportional to foot
  • Define medial edge of orthotic
44
Q

1st and 5th metatarsal heads on forefoot balance platform

A
  • 1st met head: 12 to 15 mm squares

- 5th met head: 3/4 size of medial platform

45
Q

Forefoot balance platform outcomes

A
  • 1 to 5 balancing (usually)
  • 2 to 5 balancing: metatarsus primus elevatus, plantarflexed 2nd ray deformity
  • 1 to 4 balancing: 5 th metatarsal elevatus, plantarflexed 4 th metatarsal
46
Q

Identifying the distal heel cup line of the forefoot balance platform

A
  • 1.5 to 2 cm proximal to calcaneal cuboid joint
  • Locates lateral border of medial expansion and medial border of orthotic
  • Wider orthotic = better control
47
Q

A “balance” nail is used to

A
  • Place forefoot contact parallel to ground
  • Forefoot valgus: balance nail under 5th met head
  • Forefoot varus: balance nail under 1st metatarsal
48
Q

Tools for platform construction

A
  • Plaster
  • Spatula
  • Waxed paper
49
Q

Construction of the platform

A
  • Forefoot of positive in plaster
  • When semi-set, trim proximal aspect using reference points
  • On supporting surface, superior aspect of cast in balanced position
  • Trim to medial and lateral border
  • Sand lightly to expose balance nail
50
Q

Medial expansion plaster

A
  • Allows for soft tissue expansion with midstance pronation
  • Distal to heel seat
  • Blended into balance platform
  • No plaster applied to “control point”
51
Q

Lateral expansion plaster

A
  • Allows for weight bearing soft tissue spread
  • Should not extend beyond 1 cm medial of calcaneal bisector
  • Addition around heel at 45°
  • Fabricot smooth
52
Q

Evaluation of positive

A
  • Medial expansion plaster does not alter balance plaster
  • No plaster on “control point”
  • Plaster blends smoothly into anterior balance platform
53
Q

Pressing preparation

A
  • Vacuum press
  • Cover positive with smooth material
  • Thermoplastic material
  • Heat to appropriate temperature
  • Must trim excess around heel to prevent “wrinkles”
54
Q

Pressing the orthotic

A
  • Capture contour of heel
  • Adequate material to support lateral expansion
  • Adequate material to capture medial arch
  • Medial arch contour captured
55
Q

Internal heel cup height

A
  • Higher heel cup = better control
  • Normal adults 12mm
  • Children 16mm
56
Q

Internal heel cup higher medially

A
  • Acts as buttress against STJ pronation in midstance
57
Q

Internal heel cup higher laterally

A
  • Acts as buttress against STJ during contact
58
Q

Grinding/sanding the orthotic

A
  • Distal length to middle of metatarsal heads
  • Lateral border slight curvature onto positive
  • Medial border straight for shoe gear fit
59
Q

Posting elevator

A
  • Adjusts rearfoot post height to shoe gear height
60
Q

Posting elevator placement

A
  • Division between planes in line with the long axis of calcaneus
  • Runs ~ 1 cm medial to calcaneal bisection out towards 5th met head
61
Q

Rearfoot post

A
  • Controls pronation during contact
  • Provides some subtalar joint control
  • Two planes (medial/lateral)
62
Q

Rearfoot post medial plane

A
  • Acts as a break
63
Q

Rearfoot post lateral plane

A
  • Supports inverted position
64
Q

Rearfoot post measurements

A
  • Lateral: 4° inverted
  • Medial: parallel to anterior edge of orthotic
  • Supports inverted presentation to ground
  • Prevents STJ pronation after full forefoot load
65
Q

Functional control of orthotic on the foot

A
  • Brings the ground up to the foot
  • Orthotic plate provides control during stance
  • Rearfoot post provides control during contact

Biomechanics (7 decks)

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