OCC Casting Materials & Techniques 3 — Questions and Answers
Question 1: When molding a cast, which technique is recommended to avoid creating pressure points?
- Using fingertip pressure to create contoured indentations
- Using the palm and thenar eminence to apply broad, even pressure (Correct answer)
- Applying strips of tape over the wet cast for additional support
- Rolling a dowel rod along the cast surface
Correct answer: Using the palm and thenar eminence to apply broad, even pressure
Broad palm and thenar eminence molding distributes pressure evenly, preventing focal pressure points that can cause skin breakdown.
Question 2: A fiberglass cast becomes warm during setting. This heat is primarily due to which process?
- Friction from wrapping the tape
- An exothermic polyurethane curing reaction (Correct answer)
- Oxidation of the fiberglass fibers
- Endothermic moisture absorption
Correct answer: An exothermic polyurethane curing reaction
Fiberglass tape contains a polyurethane prepolymer that undergoes an exothermic curing reaction when activated by water, generating heat.
Question 3: Which of the following best describes 'bivalving' a cast?
- Removing the cast entirely with a saw
- Cutting the cast longitudinally on two sides to create two halves (Correct answer)
- Adding a second layer of fiberglass over the primary cast
- Splitting only the padding and stockinette without cutting the cast shell
Correct answer: Cutting the cast longitudinally on two sides to create two halves
Bivalving involves making two longitudinal cuts on opposite sides of the cast, converting it into two clamshell-like halves to relieve pressure.
Question 4: For a long leg cast, the knee is typically immobilized in how many degrees of flexion?
- 0 degrees (full extension)
- 5–10 degrees of flexion
- 20–30 degrees of flexion (Correct answer)
- 45–60 degrees of flexion
Correct answer: 20–30 degrees of flexion
A long leg cast is typically applied with 20–30 degrees of knee flexion to provide stability while allowing the patient to bear weight comfortably.
Question 5: Which casting material generally has the HIGHEST tensile strength per unit weight?
- Standard plaster of Paris
- Fiberglass (polyurethane-impregnated glass fiber) (Correct answer)
- Cotton-based orthopedic padding
- Thermoplastic splint material
Correct answer: Fiberglass (polyurethane-impregnated glass fiber)
Fiberglass casting tape provides superior tensile strength at a lighter weight compared to plaster, which is why it requires fewer layers for equivalent support.
Question 6: When padding a bony prominence (e.g., the fibular head) before casting, what is the standard approach?
- Avoid padding prominences to ensure firm contact
- Apply extra layers of cast padding over the prominence (Correct answer)
- Remove all padding from the area and apply cast directly
- Use petroleum jelly over the prominence instead of padding
Correct answer: Apply extra layers of cast padding over the prominence
Extra layers of cast padding over bony prominences reduce direct pressure and the risk of pressure ulcers and nerve injuries beneath the cast.
Question 7: A cast that is too loose will most likely result in which complication?
- Compartment syndrome
- Thermal burn during curing
- Skin maceration from trapped moisture
- Malunion due to inadequate fracture immobilization (Correct answer)
Correct answer: Malunion due to inadequate fracture immobilization
A loose cast allows fracture fragments to move, potentially leading to malunion or malreduction of the fracture during the healing period.
OCC Casting Materials & Techniques 3
When molding a cast, which technique is recommended to avoid creating pressure points?