Chapter Four Flashcards
Fabrication of a metal structure usually begins with what?
Anatomical measurements to obtain the required dimensions of the body segment to be supported.
What follows anatomical measurements during the fabrication of a metal structure?
A tracing of the profile of the torso or the limb the brace is being made for.
How can tracings be taken?
Supine or standing against a wall.
How should the tracing tool stand?
Perpendicular to the paper surface and parallel to the body.
What is usually done to a tracing during metal fabrication?
The tracing is reversed.
When a total contact orthosis is being made, what is needed before fabrication?
a three-dimensional cast of the limb or torso.
What can be used when only a replica of the plantar surface of the feet is needed?
Low-density polyurethane foam to make the impression.
When making a foot impression, what might a orthotist need to do to help guide the foot?
Might need to guide the dorsum of the instep, metatarsal heads, and toes to ensure an accurate mold.
What is another way, other than cast, to get a positive model of the patient’s limb?
CAD CAM with measurements and scans.
When adding metal components to a brace, what must be considered?
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.
What is required to maintain joint congruity during fabrication?
Alignment fixture.
What must be done after contouring the bars of the brace?
The bars must be sanded and polished to get ride of any scratches or notches to prevent failure.
During metal bending, what should be done before any holes are drilled in the metal?
All bending/contouring.
How are thermoplastics formed, and what does it usually mean in regards to the orthosis?
They are vacuum formed.
The orthosis is more flexible and can be readily modified postproduction.
How are thermosets formed?
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.
How do you create a positive model from a cast?
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
When vacuum forming the mold, what must be added?
Stockinette material to wick and rapidly evacuate the air during the forming process.
What can be affected based on the choice of plastic and thickness?
Clarity
stiffness
durability
resistance to torsion.
What occurs in the vacuum forming process?
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.
What equipment is necessary to fabricate custom orthoses?
ovens
Vises
vacuum forming equipment and fixtures
Machines tools for sanding, grinding, polishing, cutting, and dust collection.
What can be added as reinforcements for the braces?
Base plastic or composite inserts
What will effect the flexibility of the brace?
Changing the trimlines
Creating corrugations
What occurs with the ankle trim lines anterior to the malleoli?
The ankle and knee are made more stable.
Trimlines posterior to the malleoli will allow more what?
Dorsiflexion and plantarflexion.
