CTO Orthotic Materials & Fabrication Techniques 3 — Questions and Answers
Question 1: Which solvent is most commonly used to bond Barge cement layers when attaching leather to thermoplastic orthotic components?
- Acetone
- Isopropyl alcohol
- Contact cement thinner (MEK) (Correct answer)
- Distilled water
Correct answer: Contact cement thinner (MEK)
MEK (methyl ethyl ketone) is the standard thinner for Barge and contact cements, maintaining proper viscosity for strong adhesion.
Question 2: A patient requires a supramalleolar orthosis (SMO) with medial longitudinal arch support. Which material combination is most appropriate for the shell?
- 3mm polypropylene with leather lining
- 1.5–2mm polypropylene with closed-cell foam liner (Correct answer)
- Carbon fiber with open-cell foam
- Neoprene with Velcro closure only
Correct answer: 1.5–2mm polypropylene with closed-cell foam liner
A 1.5–2mm polypropylene shell with closed-cell foam liner provides the necessary rigidity and cushioning for an SMO in a pediatric or adult population.
Question 3: During grinding and finishing of a thermoplastic AFO, which personal protective equipment (PPE) is essential to prevent respiratory hazard?
- Safety goggles only
- Latex gloves
- N95 or P100 respirator and safety goggles (Correct answer)
- Steel-toed boots
Correct answer: N95 or P100 respirator and safety goggles
Grinding thermoplastics generates fine particulate dust that is a respiratory hazard, requiring an N95 or P100 respirator along with eye protection.
Question 4: What does 'drop-lock' refer to in orthotic metal joint fabrication?
- A mechanism that prevents all motion at the joint
- A ring that drops over the joint to lock it in extension, which can be unlocked for sitting (Correct answer)
- A tool used to form metal uprights
- A method of attaching the orthosis to footwear
Correct answer: A ring that drops over the joint to lock it in extension, which can be unlocked for sitting
A drop-lock (ring lock) is a metal ring that slides down over the knee joint to lock it in extension, enabling stance stability while allowing removal for sitting.
Question 5: Which method is used to determine the appropriate trim line placement on an AFO to allow dorsiflexion assist while maintaining mediolateral stability?
- Trimming proximal to the malleoli only
- Trimming anterior to the malleoli for flexibility and posterior for rigidity (Correct answer)
- Extending trim lines distal to the malleoli on all sides
- Maintaining trim lines at the midline of the malleoli
Correct answer: Trimming anterior to the malleoli for flexibility and posterior for rigidity
Trim lines placed anterior to the malleoli reduce stiffness and allow dorsiflexion assist, while posterior trim lines increase rigidity.
Question 6: Which type of orthotic joint allows both plantar flexion and dorsiflexion within set limits?
- Solid ankle joint
- Oklahoma joint
- Bichannel adjustable ankle locking (BiCAAL) joint (Correct answer)
- Klenzak joint
Correct answer: Bichannel adjustable ankle locking (BiCAAL) joint
The BiCAAL joint allows independent adjustment of both dorsiflexion and plantar flexion stops, offering controlled motion in both planes.
Question 7: What is the purpose of applying a release agent to a plaster positive model before vacuum-forming thermoplastic over it?
- To color-code the model
- To prevent the thermoplastic from adhering to the plaster (Correct answer)
- To harden the plaster surface
- To reduce the forming temperature required
Correct answer: To prevent the thermoplastic from adhering to the plaster
A release agent (such as petroleum jelly or a spray release) prevents the thermoplastic from bonding to the plaster model, enabling easy removal after forming.
CTO Orthotic Materials & Fabrication Techniques 3
Which solvent is most commonly used to bond Barge cement layers when attaching leather to thermoplastic orthotic components?