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Biomechanics > 8) Casting Techniques and Orthotic Fabrication > Flashcards

8) Casting Techniques and Orthotic Fabrication Flashcards

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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
Evaluation of the negative: 1st ray
- Contour of dell - Skin lines along the declination of the first metatarsal - No transverse lines proximal to head - Indicates position of the LMTJ
26
Evaluation of the negative: contour of the heel pad
- Trisect the heel - Middle 1/3 should be flat - Medial 2/3 curved (supination of rearfoot) - Evaluates the STJ position
27
Semi-weight bearing technique
- Commonly utilized - Technically easy - Difficult to maintain STJ neutral - Indicated primarily when accommodation is desired
28
Semi-weight bearing technique is indicated primarily when
- Accommodation is desired | - Biofoam
29
Vacuum technique
- 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
Considerations when pouring the positive
Calcaneal bisection - Dell below lateral malleolus) Data from bioeval - What is NCSP? - Does foot pronate to perpendicular? - Is it maximally pronated at ?
31
Pouring the positive
- 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
Pouring the negative: vertical
- When STJ motion is adequate and the calcaneus can evert beyond perpendicular
33
Pouring the negative: inverted
- When STJ motion is limited and the calcaneus cannot evert to perpendicular
34
Pouring the negative: everted
- When STJ is in a fixed everted position or cannot invert to perpendicular
35
Preparing for balancing
- Negative is removed - “Menesci” rasped away - “Fabricot” is used to smooth the surface - Dye in positive prevents removal of excessive plaster
36
Concept of balancing
- Provide MTJ control - Custom made walking surface - Eliminate compensation which results in abnormal foot mechanics
37
Why intrinsically balance?
- To support the forefoot deformity and prevent midstance STJ compensation - Brings the “ground up to the foot” - Enables better fit in shoe gear
38
Extrinsic balancing
- No balancing of positive cast | - Forefoot balance platform added to orthotic plate
39
Extrinsic vs. intrinsic balancing
- Best shoe fit = intrinsic - Fewest problems = intrinsic - Best support of forefoot deformity = extrinsic
40
When rigid forefoot valgus or varus exists, use
- Extrinsic post
41
When the forefoot deformity is > 5 degrees, use
- A combination of balancing techniques
42
Steps in preparing the positive
- Forefoot balance platform (supports the forefoot deformity) - Medial expansion (allows for expansion with normal midstance pronation) - Lateral expansion (fat pad displacement)
43
Forefoot balance platform purpose
- 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
1st and 5th metatarsal heads on forefoot balance platform
- 1st met head: 12 to 15 mm squares | - 5th met head: 3/4 size of medial platform
45
Forefoot balance platform outcomes
- 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
Identifying the distal heel cup line of the forefoot balance platform
- 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
A “balance” nail is used to
- Place forefoot contact parallel to ground - Forefoot valgus: balance nail under 5th met head - Forefoot varus: balance nail under 1st metatarsal
48
Tools for platform construction
- Plaster - Spatula - Waxed paper
49
Construction of the platform
- 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
Medial expansion plaster
- Allows for soft tissue expansion with midstance pronation - Distal to heel seat - Blended into balance platform - No plaster applied to “control point”
51
Lateral expansion plaster
- 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
Evaluation of positive
- Medial expansion plaster does not alter balance plaster - No plaster on “control point” - Plaster blends smoothly into anterior balance platform
53
Pressing preparation
- Vacuum press - Cover positive with smooth material - Thermoplastic material - Heat to appropriate temperature - Must trim excess around heel to prevent “wrinkles”
54
Pressing the orthotic
- Capture contour of heel - Adequate material to support lateral expansion - Adequate material to capture medial arch - Medial arch contour captured
55
Internal heel cup height
- Higher heel cup = better control - Normal adults 12mm - Children 16mm
56
Internal heel cup higher medially
- Acts as buttress against STJ pronation in midstance
57
Internal heel cup higher laterally
- Acts as buttress against STJ during contact
58
Grinding/sanding the orthotic
- Distal length to middle of metatarsal heads - Lateral border slight curvature onto positive - Medial border straight for shoe gear fit
59
Posting elevator
- Adjusts rearfoot post height to shoe gear height
60
Posting elevator placement
- Division between planes in line with the long axis of calcaneus - Runs ~ 1 cm medial to calcaneal bisection out towards 5th met head
61
Rearfoot post
- Controls pronation during contact - Provides some subtalar joint control - Two planes (medial/lateral)
62
Rearfoot post medial plane
- Acts as a break
63
Rearfoot post lateral plane
- Supports inverted position
64
Rearfoot post measurements
- Lateral: 4° inverted - Medial: parallel to anterior edge of orthotic - Supports inverted presentation to ground - Prevents STJ pronation after full forefoot load
65
Functional control of orthotic on the foot
- 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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