CPT Prosthetic Fabrication & Assembly Techniques 3 — Questions and Answers
Question 1: Which vacuum level range is recommended during diagnostic socket lamination to ensure adequate resin infusion without voids?
- 5–10 inHg
- 15–20 inHg
- 25–29 inHg (Correct answer)
- 30–35 inHg
Correct answer: 25–29 inHg
A vacuum level of 25–29 inHg (near atmospheric) ensures thorough resin wet-out and void-free lamination in prosthetic socket fabrication.
Question 2: A transfemoral socket exhibits a medial brim that is too high, likely causing:
- Abductor lurch during gait
- Perineal pressure and adductor roll (Correct answer)
- Lateral trunk lean away from prosthetic side
- Inadequate suspension
Correct answer: Perineal pressure and adductor roll
An overly high medial brim creates pressure against the perineum and adductor tissue, commonly called adductor roll.
Question 3: When grinding the inner surface of a laminated socket to relieve a pressure area, the technician should use:
- A carbide router bit at high speed
- A drum sander at low speed with light pressure (Correct answer)
- A flap disc grinder
- A wire wheel attachment
Correct answer: A drum sander at low speed with light pressure
A drum sander at low speed with light pressure allows controlled, gradual material removal without burning or delaminating the composite layers.
Question 4: The primary function of a flexible inner socket (FIS) combined with a rigid frame is to:
- Increase overall socket wall thickness for durability
- Allow soft-tissue displacement while maintaining structural integrity (Correct answer)
- Eliminate the need for suspension sleeves
- Reduce fabrication time compared to single-wall sockets
Correct answer: Allow soft-tissue displacement while maintaining structural integrity
A flexible inner socket allows the residual limb tissues to expand and displace naturally, while the rigid outer frame maintains alignment and structural support.
Question 5: During exoskeletal (crustacean) prosthesis fabrication, the wood block carving for the thigh section must be shaped to accommodate:
- Cosmetic appearance only, with no functional requirements
- Structural load transfer along the medial and lateral walls (Correct answer)
- Only the distal end attachment point
- The pelvic band attachment brackets
Correct answer: Structural load transfer along the medial and lateral walls
The carved wood shank of an exoskeletal prosthesis must distribute structural loads along the medial and lateral walls to maintain integrity during ambulation.
Question 6: What is the correct torque specification process when installing a pyramid adapter to a prosthetic foot?
- Hand-tighten until snug, then add one quarter turn
- Use a torque wrench set to the manufacturer's specified value (Correct answer)
- Tighten until the adapter does not rotate under body weight
- Apply thread-locking compound and tighten to maximum resistance
Correct answer: Use a torque wrench set to the manufacturer's specified value
Manufacturers specify precise torque values for pyramid adapters; using a calibrated torque wrench prevents under- or over-tightening that could cause component failure.
Question 7: When fabricating a supracondylar suspension transtibial socket (SC/SP), the medial and lateral trim lines must be:
- Below the femoral condyles to avoid bony prominences
- Above the femoral condyles to capture them for suspension (Correct answer)
- At the level of the fibular head
- Even with the patellar tendon bar
Correct answer: Above the femoral condyles to capture them for suspension
The SC/SP design achieves suspension by extending the socket trim lines above the femoral condyles, locking the socket onto the condyles.
CPT Prosthetic Fabrication & Assembly Techniques 3
Which vacuum level range is recommended during diagnostic socket lamination to ensure adequate resin infusion without voids?