CPT Prosthetic Components & Technology 1 — Questions and Answers
Question 1: Which prosthetic foot category is designed to store and return energy during the gait cycle, making it most suitable for active ambulators?
- SACH foot
- Single-axis foot
- Energy-storing carbon fiber foot (Correct answer)
- Multi-axial foot
Correct answer: Energy-storing carbon fiber foot
Energy-storing carbon fiber feet (dynamic response feet) flex during loading and release energy at toe-off, benefiting active and athletic users.
Question 2: What is the primary function of a torsion adapter in a lower-limb prosthesis?
- Provide vertical shock absorption
- Allow transverse plane rotation to reduce shear forces on the residual limb (Correct answer)
- Control knee flexion angle during swing phase
- Connect the pylon to the prosthetic foot
Correct answer: Allow transverse plane rotation to reduce shear forces on the residual limb
A torsion adapter permits horizontal rotation between the socket and foot, reducing rotational shear forces transmitted to the residual limb during activities like pivoting.
Question 3: A SACH (Solid Ankle Cushion Heel) foot achieves its shock absorption and pseudo-plantarflexion through which mechanism?
- A mechanical hinge at the ankle joint
- Compression of a foam or rubber heel wedge (Correct answer)
- A carbon fiber keel that deflects under load
- A hydraulic cylinder within the ankle block
Correct answer: Compression of a foam or rubber heel wedge
The SACH foot has no mechanical joint; instead, a compressible foam or rubber heel cushion simulates plantarflexion at heel strike.
Question 4: Which knee unit mechanism uses fluid resistance that automatically adjusts cadence-responsive damping during swing phase?
- Constant-friction mechanical knee
- Polycentric four-bar linkage knee
- Pneumatic or hydraulic cadence-responsive knee (Correct answer)
- Manual-locking knee
Correct answer: Pneumatic or hydraulic cadence-responsive knee
Pneumatic and hydraulic cadence-responsive knee units vary swing-phase resistance in proportion to walking speed, allowing more natural gait at multiple cadences.
Question 5: A polycentric (four-bar linkage) prosthetic knee provides which key advantage over a single-axis knee?
- Greater maximum weight capacity
- Instantaneous center of rotation that moves posteriorly during stance, improving stability (Correct answer)
- Built-in microprocessor control
- Lower overall component cost
Correct answer: Instantaneous center of rotation that moves posteriorly during stance, improving stability
The four-bar linkage geometry shifts the effective center of rotation posteriorly during weight-bearing, creating an inherently more stable stance phase without a mechanical lock.
Question 6: In upper-limb prosthetics, a body-powered hook terminal device is typically activated by which harness motion?
- Shoulder depression
- Scapular abduction (forward reach) via a figure-8 harness (Correct answer)
- Elbow flexion
- Wrist pronation
Correct answer: Scapular abduction (forward reach) via a figure-8 harness
Scapular abduction generated by forward reach transmits force through the control cable of a figure-8 harness to open the voluntary-opening hook.
Question 7: Which component is used between a transtibial socket and a prosthetic foot to provide a cosmetically acceptable leg shape while protecting internal components?
- Suspension sleeve
- Endoskeletal pylon with foam cover (Correct answer)
- Exoskeletal (crustacean) shell
- Liner with locking pin
Correct answer: Endoskeletal pylon with foam cover
An endoskeletal pylon covered with a shaped foam cover provides both structural support and cosmetic appearance in a modular transtibial prosthesis.
CPT Prosthetic Components & Technology 1
Which prosthetic foot category is designed to store and return energy during the gait cycle, making it most suitable for active ambulators?