CPT Maintenance, Repairs, & Quality Assurance 3 — Questions and Answers
Question 1: Which type of corrosion is MOST commonly observed at the interface between an aluminum pylon and a stainless steel component in a prosthetic system?
- Galvanic corrosion (Correct answer)
- Crevice corrosion
- Pitting corrosion
- Uniform corrosion
Correct answer: Galvanic corrosion
Galvanic corrosion occurs when two dissimilar metals (aluminum and stainless steel) are in electrical contact in the presence of moisture, accelerating oxidation of the less noble metal.
Question 2: When performing a static structural test on a transtibial prosthesis, the load is applied at what angle to simulate worst-case forefoot loading?
- 15° anterior from vertical (Correct answer)
- 0° (pure vertical compression)
- 45° posterior from vertical
- 30° lateral from vertical
Correct answer: 15° anterior from vertical
ISO 10328 structural testing applies loads at approximately 15° anterior to simulate the forefoot loading vector encountered during terminal stance.
Question 3: A technician is repairing a cracked thermoplastic socket. After spot-heating and reshaping the crack area, the MOST important final quality step is:
- Checking wall thickness with calipers at the repaired site (Correct answer)
- Smoothing the inner surface with wet/dry sandpaper
- Applying a protective lacquer coating over the repair
- Verifying color match with the original socket material
Correct answer: Checking wall thickness with calipers at the repaired site
After any thermal repair to a thermoplastic socket, wall thickness must be verified because reheating can thin the material and compromise structural integrity.
Question 4: A hydraulic ankle-foot prosthetic component requires fluid replacement. The technician's PRIMARY reference for fluid type and volume should be:
- Manufacturer's service manual for that specific component (Correct answer)
- General prosthetic hydraulics reference textbook
- Previous technician's repair notes in the patient file
- The viscosity grade printed on the original fluid container
Correct answer: Manufacturer's service manual for that specific component
Only the manufacturer's service manual contains exact fluid type, viscosity, and fill volume specifications validated for that specific hydraulic component.
Question 5: Which condition MOST directly indicates that a prosthetic liner requires replacement rather than continued use?
- Visible pinhole perforations in the liner wall (Correct answer)
- Minor discoloration from body oils
- Surface abrasion on the exterior of the liner
- Temporary loss of tackiness after washing
Correct answer: Visible pinhole perforations in the liner wall
Pinhole perforations break the sealed interface required for suspension, making the liner functionally unsafe and necessitating immediate replacement.
Question 6: During final QA of a transfemoral prosthesis, the technician observes that the hip joint axis of the prosthetic knee is set 5° internally rotated. This will MOST likely result in:
- Whip during swing phase (Correct answer)
- Lateral trunk shift during stance
- Excessive knee flexion at initial contact
- Pistoning during mid-swing
Correct answer: Whip during swing phase
Internal rotation misalignment of the knee axis causes a medial or lateral whip (medial whip in this case) as the foot deviates during swing phase.
Question 7: A patient returns with a broken stainless steel ankle bolt in a dynamic response foot. The CORRECT repair procedure is to:
- Extract the broken bolt, clean the threads, and install a new OEM-specified bolt torqued to spec (Correct answer)
- Drill out the bolt hole and install a slightly larger replacement bolt
- Apply thread-locking adhesive over the broken stub and use a set-screw overlay
- Weld the new bolt in place for permanent fixation
Correct answer: Extract the broken bolt, clean the threads, and install a new OEM-specified bolt torqued to spec
Proper procedure requires extracting the broken fastener, inspecting threads, and replacing with the OEM-specified bolt torqued to manufacturer specification to restore full structural integrity.
CPT Maintenance, Repairs, & Quality Assurance 3
Which type of corrosion is MOST commonly observed at the interface between an aluminum pylon and a stainless steel component in a prosthetic system?