Chapter Four

Question 1

Fabrication of a metal structure usually begins with what?

Answer 1

Anatomical measurements to obtain the required dimensions of the body segment to be supported.

Question 2

What follows anatomical measurements during the fabrication of a metal structure?

Answer 2

A tracing of the profile of the torso or the limb the brace is being made for.

Question 3

How can tracings be taken?

Answer 3

Supine or standing against a wall.

Question 4

How should the tracing tool stand?

Answer 4

Perpendicular to the paper surface and parallel to the body.

Question 5

What is usually done to a tracing during metal fabrication?

Answer 5

The tracing is reversed.

Question 6

When a total contact orthosis is being made, what is needed before fabrication?

Answer 6

a three-dimensional cast of the limb or torso.

Question 7

What can be used when only a replica of the plantar surface of the feet is needed?

Answer 7

Low-density polyurethane foam to make the impression.

Question 8

When making a foot impression, what might a orthotist need to do to help guide the foot?

Answer 8

Might need to guide the dorsum of the instep, metatarsal heads, and toes to ensure an accurate mold.

Question 9

What is another way, other than cast, to get a positive model of the patient’s limb?

Answer 9

CAD CAM with measurements and scans.

Question 10

When adding metal components to a brace, what must be considered?

Answer 10

The two-dimensional tracing is used, the model must be laid out to ensure proper device fit.
The joints must be at the proper axis location
They must be square or parallel in all places
Clearance between the patient’s bony anatomy and the mechanical joints must be optimal. The sidebar material is contoured to the profile of the tracing
The bands are matched to the profile of the leg in the sagittal plane.

Question 11

What is required to maintain joint congruity during fabrication?

Answer 11

Alignment fixture.

Question 12

What must be done after contouring the bars of the brace?

Answer 12

The bars must be sanded and polished to get ride of any scratches or notches to prevent failure.

Question 13

During metal bending, what should be done before any holes are drilled in the metal?

Answer 13

All bending/contouring.

Question 14

How are thermoplastics formed, and what does it usually mean in regards to the orthosis?

Answer 14

They are vacuum formed.

The orthosis is more flexible and can be readily modified postproduction.

Question 15

How are thermosets formed?

Answer 15

They go through a polymerization process.
The orthosis is usually more rigid and cannot be heat modified postproduction without destroying the molecular strucutre of the plastic.

Question 16

How do you create a positive model from a cast?

Answer 16

The positive model is sealed. Liquid molding plaster is mixed and poured into the mold. A metal mandrel is placed into the plaster, and once the plaster has hardened, the mandrel is used in a special vise to hold the positive model. The indelible pencil marks will have transferred onto the model but may need to be reinforced. The model is smoothed, and the bony areas, and join fixture/dummies are added

Question 17

When vacuum forming the mold, what must be added?

Answer 17

Stockinette material to wick and rapidly evacuate the air during the forming process.

Question 18

What can be affected based on the choice of plastic and thickness?

Answer 18

Clarity
stiffness
durability
resistance to torsion.

Question 19

What occurs in the vacuum forming process?

Answer 19

A sheet of plastic is heated until it is flexible and autoadhesive, then draping the plastic over the positive model and applying vacuum to remove all of the air between the plastic and the model.

Question 20

What equipment is necessary to fabricate custom orthoses?

Answer 20

ovens
Vises
vacuum forming equipment and fixtures
Machines tools for sanding, grinding, polishing, cutting, and dust collection.

Question 21

What can be added as reinforcements for the braces?

Answer 21

Base plastic or composite inserts

Question 22

What will effect the flexibility of the brace?

Answer 22

Changing the trimlines

Creating corrugations

Question 23

What occurs with the ankle trim lines anterior to the malleoli?

Answer 23

The ankle and knee are made more stable.

Question 24

Trimlines posterior to the malleoli will allow more what?

Answer 24

Dorsiflexion and plantarflexion.

Question 25

What is another way of producing localized stiffness?

Answer 25

Placing a corrugation on the exterior of the model.

Question 26

Once the plastic has been removed from the positive model, what happenes?

Answer 26

The initial trim lines are established and the edges are polished smooth to prevent both rough spots that could scratch the skin and stress risers that could result in early failure of the plastic.

Question 27

What should you do if the plastic edges impinge on the patient’s skin?

Answer 27

Flare the edges away from the body.

Question 28

What are the two ways to flare the edges of a brace?

Answer 28

Heat modification or beveling the inside edge of the plastic.

Question 29

When an all around more rigid orthosis is desired, what can be used?

Answer 29

Thermoset lamination materials

Question 30

What are the most common resins used for orthoses during thermoset fabrication?

Answer 30

Polyester
Epoxy
Acrylic

Question 31

What are the most common fabrics used for an orthosis during thermoset fabrication?

Answer 31

Nylon
Carbon fiber
Kevlar.

Question 32

What determines the resin and matrix used for lamination?

Answer 32

The functional goals and structural strength desired

Question 33

How is vacuum assisted lamination done?

Answer 33

The model is prepared the same way as vacuum-formed thermoplastic orthosis. However, a polyvinyl alcohol (PVA) bag is placed over the modified model and evacuated. The layers of the reinforcing fabrics are then stretched taut over the model. A second PVA bag is placed over the fabric and attached to a vacuum source. A catalyst that changes the monomer resin into the polymer is added to the resin, the resin is poured into the PVA bag and the negative pressure caused by the vacuum source pulls the resin into the mold., saturating the fabric. Once the chemical reaction has occurred, the vacuum is shut off and plastic component is removed from the model.

Question 34

How is the CAM process achieved?

Answer 34

The rectified positive model is carved from rigid foam blanks on CAM lathe. The modified data from the CAD process are either downladed to a carver in the facility or sent to central fab. Once the model has been carved, the orthosis is fabricated in the normal manner using thermoplastic or thermoset materials.

Question 35

What can CAM be used for?

Answer 35

Spinal orthoses
Plagiaocephaly cranial orthoses
Knee orthoses
Also prefabricated braces.