CPO Prosthetic & Orthotic Design & Fabrication 3 — Questions and Answers
Question 1: In the fabrication of a patellar tendon bearing (PTB) transtibial socket, the area over the fibular head should be:
- Relieved to avoid peroneal nerve compression (Correct answer)
- Loaded equally with surrounding tissue
- Built up to improve mediolateral stability
- Trimmed short to allow free knee flexion
Correct answer: Relieved to avoid peroneal nerve compression
The fibular head area must be relieved in the PTB socket to prevent compression of the superficial peroneal nerve and subsequent neuropathy.
Question 2: Which joint design in a knee-ankle-foot orthosis (KAFO) allows for free motion during swing phase while providing stance-phase stability?
- Stance control (SCKAFO) orthotic knee joint (Correct answer)
- Drop ring lock joint
- Offset knee joint
- Bail lock joint
Correct answer: Stance control (SCKAFO) orthotic knee joint
Stance control KAFO joints automatically lock during weight acceptance and unlock during swing to allow free knee flexion and improve gait efficiency.
Question 3: The primary advantage of using a flexible inner socket within a rigid outer frame (flexible socket design) for transfemoral amputees is:
- Improved comfort and tissue accommodation during dynamic activity (Correct answer)
- Increased structural strength under high loads
- Simplified fabrication process
- Better heat dissipation due to rigid material
Correct answer: Improved comfort and tissue accommodation during dynamic activity
The flexible inner socket (typically polyethylene) conforms to soft tissue changes during activity, improving comfort and reducing pressure peaks.
Question 4: When fabricating a TLSO for scoliosis management, the three-point pressure system primarily works by applying corrective force at the:
- Apex of the curve and two counter-pressure points above and below (Correct answer)
- Bilateral iliac crests only
- Thoracic kyphosis apex
- Lumbar lordosis apex bilaterally
Correct answer: Apex of the curve and two counter-pressure points above and below
The three-point system applies a primary corrective force at the curve apex with reciprocal counter-forces above and below to produce lateral correction.
Question 5: What is the correct sequence for laminating a carbon fiber prosthetic socket using wet lay-up technique?
- Apply resin to fabric layers, lay over positive model, apply vacuum, cure (Correct answer)
- Cure resin first, then apply fabric, then vacuum
- Apply fabric dry, cure, then saturate with resin
- Saturate fabric, cure in oven, then apply vacuum post-cure
Correct answer: Apply resin to fabric layers, lay over positive model, apply vacuum, cure
Wet lay-up involves saturating reinforcement fabric with resin, draping it over the model, applying vacuum for consolidation, and then allowing cure.
Question 6: Which suspension mechanism is contraindicated in a patient with a transfemoral amputation who has significant skin integrity issues on the distal residual limb?
- Suction socket with distal one-way valve (Correct answer)
- Hip belt and pelvic band
- Silesian belt
- Neoprene suspension sleeve
Correct answer: Suction socket with distal one-way valve
Suction suspension concentrates shear and normal forces at the distal residual limb, which can exacerbate existing skin integrity problems.
Question 7: For fabricating a custom foot orthosis to address plantar fasciitis, the posting strategy that best offloads the medial heel is:
- Medial heel skive with rearfoot varus post (Correct answer)
- Lateral rearfoot valgus post
- Forefoot valgus intrinsic post
- Full-length flat accommodative insert
Correct answer: Medial heel skive with rearfoot varus post
A medial heel skive combined with a rearfoot varus post supinates the subtalar joint and reduces tension on the plantar fascia insertion.
CPO Prosthetic & Orthotic Design & Fabrication 3
In the fabrication of a patellar tendon bearing (PTB) transtibial socket, the area over the fibular head should be: