CPT Prosthetic Fabrication & Assembly Techniques 2 — Questions and Answers
Question 1: Which lamination resin type offers the highest strength-to-weight ratio for prosthetic sockets?
- Polyester resin
- Epoxy resin (Correct answer)
- Acrylic resin
- Urethane resin
Correct answer: Epoxy resin
Epoxy resin provides the highest strength-to-weight ratio among lamination resins commonly used in prosthetic socket fabrication.
Question 2: During check socket fabrication for a transtibial amputee, the primary purpose of using clear thermoplastic is to:
- Reduce fabrication time
- Visualize tissue contact and pressure areas (Correct answer)
- Improve patient comfort immediately
- Permanently replace the definitive socket
Correct answer: Visualize tissue contact and pressure areas
Clear thermoplastic check sockets allow the clinician to observe skin blanching, tissue displacement, and contact patterns during fitting.
Question 3: When bench-aligning a SACH foot to a transtibial prosthesis, the foot should be set with:
- 5–7° of toe-out and slight plantar flexion (Correct answer)
- Neutral toe angle and 5° dorsiflexion
- 10° of toe-in and neutral ankle
- Neutral toe angle and slight plantar flexion
Correct answer: 5–7° of toe-out and slight plantar flexion
A SACH foot is bench-aligned with 5–7° of toe-out to mimic the natural gait angle and slight plantar flexion to encourage heel loading.
Question 4: What is the correct sequence of steps when fabricating a thermoplastic transfemoral socket using direct forming?
- Heat plastic → drape over cast → trim → add suspension (Correct answer)
- Trim → heat plastic → drape over cast → add suspension
- Add suspension → heat plastic → drape over cast → trim
- Drape over cast → heat plastic → trim → add suspension
Correct answer: Heat plastic → drape over cast → trim → add suspension
The direct forming process begins with heating the thermoplastic sheet, draping it over the positive model, trimming after cooling, then adding suspension components.
Question 5: Which reinforcement fiber orientation provides the greatest resistance to torsional stress in a prosthetic pylon?
- Unidirectional 0°
- Unidirectional 90°
- ±45° bias weave (Correct answer)
- Plain weave 0°/90°
Correct answer: ±45° bias weave
A ±45° bias weave orientation is most effective at resisting torsional (shear) loads in composite structures like prosthetic pylons.
Question 6: When using a pull-through lamination technique, the stockinette layers are arranged so that:
- All layers run parallel to the socket brim
- Innermost nylon is pulled through last after all reinforcement layers (Correct answer)
- Outermost cosmetic stocking is applied first
- Carbon fiber is placed directly against the positive model
Correct answer: Innermost nylon is pulled through last after all reinforcement layers
In pull-through lamination, the inner nylon stockinette is pulled through the carbon and fiberglass layers last to create a smooth inner socket surface.
Question 7: To achieve proper pistoning control in a pin-lock suspension system, the technician must ensure:
- The shuttle pin length equals the liner thickness
- The pin engages the locking mechanism at full knee extension only
- The liner pin length matches the distal socket receiver depth (Correct answer)
- The pin is made of carbon fiber for reduced weight
Correct answer: The liner pin length matches the distal socket receiver depth
Proper fit requires the liner's pin length to match the receiver depth so the lock engages securely without bottoming out or incomplete engagement.
CPT Prosthetic Fabrication & Assembly Techniques 2
Which lamination resin type offers the highest strength-to-weight ratio for prosthetic sockets?