CTO Orthotic Materials & Fabrication Techniques 5 — Questions and Answers
Question 1: Which property of low-temperature thermoplastics (LTT) makes them particularly useful for upper-extremity orthoses fabricated directly on the patient?
- They require oven heating to 400°F for activation
- They soften at temperatures safe for skin contact (around 60–70°C) and conform directly to the patient (Correct answer)
- They are rigid at all temperatures
- They must be vacuum-formed over a plaster model
Correct answer: They soften at temperatures safe for skin contact (around 60–70°C) and conform directly to the patient
LTTs soften at temperatures safe for direct skin contact, allowing the therapist or technician to mold them directly on the patient for precise conformity.
Question 2: In metal upright fabrication for a KAFO, which process is used to form a contoured shape in the metal upright to follow the anatomy of the limb?
- Cold rolling
- Annealing and bending with a bending iron (Correct answer)
- Electroplating
- Welding two straight sections
Correct answer: Annealing and bending with a bending iron
Annealing softens the metal and bending with a bending iron allows the upright to be contoured to match limb anatomy without cracking.
Question 3: What does the term 'check socket' refer to in orthotic and prosthetic practice?
- A metal socket used for final fitting
- A transparent or preliminary test socket used to verify fit before fabricating the definitive device (Correct answer)
- A socket cover for cosmetic purposes
- A standardized prefabricated socket
Correct answer: A transparent or preliminary test socket used to verify fit before fabricating the definitive device
A check socket is a diagnostic/test socket, often made from transparent thermoplastic, used to evaluate fit and alignment before fabricating the final device.
Question 4: Which surface treatment improves adhesion when bonding two polypropylene surfaces together using contact cement?
- Waxing the surface
- Sanding the surface with coarse grit paper to roughen it (Correct answer)
- Cooling the surface with ice
- Applying a primer coat of silicone
Correct answer: Sanding the surface with coarse grit paper to roughen it
Roughening the polypropylene surface with coarse sandpaper increases surface area and mechanical interlocking sites, significantly improving adhesive bond strength.
Question 5: When fabricating a wrist-hand orthosis (WHO) from low-temperature thermoplastic, which wrist position is most commonly used for a resting hand splint?
- Full wrist flexion with fingers extended
- Wrist in 20–30° extension, MCPs in 45–70° flexion, IPs slightly flexed, thumb abducted (Correct answer)
- Wrist and fingers in full extension
- Wrist in neutral with fingers fully flexed
Correct answer: Wrist in 20–30° extension, MCPs in 45–70° flexion, IPs slightly flexed, thumb abducted
The intrinsic-plus or safe position (wrist 20–30° extension, MCPs flexed, IPs extended) prevents contracture and is the standard for resting hand splints.
Question 6: Which characteristic distinguishes open-cell foam from closed-cell foam in orthotic applications?
- Open-cell foam is rigid; closed-cell foam is flexible
- Open-cell foam absorbs moisture and compresses more readily; closed-cell foam resists moisture and holds its shape longer (Correct answer)
- Open-cell foam is only used for rigid orthoses
- Closed-cell foam is always softer than open-cell foam
Correct answer: Open-cell foam absorbs moisture and compresses more readily; closed-cell foam resists moisture and holds its shape longer
Open-cell foam absorbs sweat and compresses more quickly (bottoms out), while closed-cell foam resists moisture and maintains its cushioning properties longer.
Question 7: During resin lamination, what is the role of the catalyst (hardener) added to polyester or epoxy resin?
- To thin the resin for easier application
- To initiate the chemical cross-linking reaction that hardens the resin (Correct answer)
- To add color pigment to the laminate
- To slow the curing process indefinitely
Correct answer: To initiate the chemical cross-linking reaction that hardens the resin
The catalyst (hardener) initiates the exothermic cross-linking (polymerization) reaction that converts liquid resin into a rigid, durable thermoset composite.
CTO Orthotic Materials & Fabrication Techniques 5
Which property of low-temperature thermoplastics (LTT) makes them particularly useful for upper-extremity orthoses fabricated directly on the patient?