OCC Casting Materials & Techniques 2 — Questions and Answers
Question 1: What is the primary chemical reaction that causes plaster of Paris to harden?
- Polymerization of resin monomers
- Hydration of calcium sulfate hemihydrate (Correct answer)
- Oxidation of calcium carbonate
- Cross-linking of polyurethane chains
Correct answer: Hydration of calcium sulfate hemihydrate
Plaster of Paris hardens through hydration: calcium sulfate hemihydrate reacts with water to form calcium sulfate dihydrate (gypite).
Question 2: Which type of cast material is preferred when the patient requires MRI imaging during the treatment period?
- Fiberglass with aluminum splints
- Standard plaster of Paris
- Fiberglass with fiberglass splints (Correct answer)
- Plaster with metal reinforcement rods
Correct answer: Fiberglass with fiberglass splints
Fiberglass cast materials are MRI-compatible because they contain no ferromagnetic metals, making them safe in magnetic fields.
Question 3: When applying a short arm cast, the wrist should typically be positioned in how many degrees of dorsiflexion?
- 0 degrees (neutral)
- 10–20 degrees (Correct answer)
- 30–45 degrees
- 50–60 degrees
Correct answer: 10–20 degrees
The wrist is typically positioned in 10–20 degrees of dorsiflexion for a functional short arm cast, allowing optimal hand function.
Question 4: What is the purpose of the 'ear' or 'window' cut into a cast?
- To reduce weight of the cast
- To allow inspection or relieve pressure over a specific area (Correct answer)
- To improve cast ventilation and reduce sweating
- To facilitate cast removal with a cast saw
Correct answer: To allow inspection or relieve pressure over a specific area
A cast window allows the clinician to inspect the underlying skin, relieve localized pressure, or access a wound beneath the cast.
Question 5: Fiberglass casting tape should be dipped in water at approximately what temperature for optimal working time?
- Ice-cold water (0–5°C)
- Room temperature water (20–25°C) (Correct answer)
- Warm water (35–40°C)
- Hot water (50–60°C)
Correct answer: Room temperature water (20–25°C)
Room temperature water is recommended for fiberglass tape to provide adequate working time; warm water accelerates the setting reaction.
Question 6: Which condition is a CONTRAINDICATION to circumferential casting immediately after acute injury?
- Stable mid-shaft radius fracture
- Significant anticipated swelling (acute compartment risk) (Correct answer)
- Buckle fracture in a pediatric patient
- Chronic stress fracture of the metatarsal
Correct answer: Significant anticipated swelling (acute compartment risk)
Circumferential casts applied when significant swelling is expected can compress neurovascular structures, causing compartment syndrome.
Question 7: What is the recommended number of layers of stockinette that should extend beyond each end of a standard cast?
- No stockinette extension is used
- 1 layer folded back 1–2 cm
- 2–5 cm of stockinette folded back over the cast edges (Correct answer)
- Stockinette is folded back 10–15 cm for maximum padding
Correct answer: 2–5 cm of stockinette folded back over the cast edges
Approximately 2–5 cm of stockinette is folded back over the cast edges and incorporated to create a smooth, padded border that prevents skin irritation.
OCC Casting Materials & Techniques 2
What is the primary chemical reaction that causes plaster of Paris to harden?