CTO Orthotic Materials & Fabrication Techniques 4 — Questions and Answers
Question 1: When fabricating a thoracolumbosacral orthosis (TLSO), which thermoplastic gauge is typically used for the rigid shell to provide adequate trunk support for an adult patient?
- 1/8 inch (3.2mm)
- 3/16 inch (4.8mm) (Correct answer)
- 1/4 inch (6.4mm)
- 1/32 inch (0.8mm)
Correct answer: 3/16 inch (4.8mm)
A 3/16-inch (4.8mm) polypropylene sheet provides sufficient rigidity for a custom TLSO while remaining manageable for fabrication.
Question 2: In a prefabricated orthosis modification, which technique is used to expand a tight area in a thermoplastic orthosis without compromising its structural integrity?
- Cutting out and patching with fiberglass
- Spot-heating with a heat gun to locally expand the material (Correct answer)
- Replacing the entire orthosis
- Adding extra padding to the outside of the shell
Correct answer: Spot-heating with a heat gun to locally expand the material
Spot-heating with a heat gun allows the technician to locally soften and expand a tight area without requiring full replacement of the orthosis.
Question 3: Which type of liner material is most appropriate for a patient with diabetic neuropathy requiring a custom foot orthosis?
- Hard cork
- Rigid graphite
- Plastazote (polyethylene foam) (Correct answer)
- Rubber heel wedge only
Correct answer: Plastazote (polyethylene foam)
Plastazote is the preferred liner for diabetic patients because it is soft, moldable, and reduces shear and pressure on insensate tissue.
Question 4: What is the function of a posterior leaf spring (PLS) AFO design compared to a solid ankle AFO?
- It provides rigid ankle support in all planes
- It allows controlled dorsiflexion while providing a dorsiflexion assist during swing phase (Correct answer)
- It is used only for plantar fasciitis management
- It locks the ankle in neutral to prevent all motion
Correct answer: It allows controlled dorsiflexion while providing a dorsiflexion assist during swing phase
A posterior leaf spring AFO flexes at the trim lines to store energy during stance and release it as a dorsiflexion assist during swing, aiding foot clearance.
Question 5: During the casting process for a custom orthosis, what does 'subtalar neutral' position mean for the foot and ankle?
- Maximum pronation of the subtalar joint
- Maximum supination of the subtalar joint
- The position where the subtalar joint is neither pronated nor supinated (Correct answer)
- Full plantar flexion of the ankle
Correct answer: The position where the subtalar joint is neither pronated nor supinated
Subtalar neutral is the position where the subtalar joint is midway between maximum pronation and supination, used as a functional reference for orthotic casting.
Question 6: Which adhesive is most appropriate for bonding Velfoam or Pelite padding to the interior of a polypropylene orthosis?
- Epoxy resin
- Hot glue gun adhesive
- Contact (Barge) cement (Correct answer)
- Super glue (cyanoacrylate)
Correct answer: Contact (Barge) cement
Contact cement such as Barge provides a flexible, durable bond between foam padding and polypropylene that withstands the mechanical stresses of orthotic wear.
Question 7: When finishing the edges of a thermoplastic orthosis, which tool is most appropriate for creating a smooth, rounded edge to prevent skin irritation?
- Table saw
- Orbital sander with fine-grit paper and a flap wheel (Correct answer)
- Router with straight bit
- Chisel
Correct answer: Orbital sander with fine-grit paper and a flap wheel
An orbital sander with fine-grit paper followed by a flap wheel creates smooth, rounded orthotic edges that prevent pressure sores and skin irritation.
CTO Orthotic Materials & Fabrication Techniques 4
When fabricating a thoracolumbosacral orthosis (TLSO), which thermoplastic gauge is typically used for the rigid shell to provide adequate trunk support for an adult patient?