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ABC CPO practice questions

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Question 1Prosthetics

Which socket design principle is most important for a transtibial prosthesis to distribute pressure over the patellar tendon bar?

  1. Suspension by a single distal pin
  2. Localized loading only on the distal tibia
  3. Total surface bearing over the entire residual limb Correct answer.
  4. A rigid non-contoured proximal brim

Explanation

Patellar tendon-bearing (PTB) designs concentrate load on pressure-tolerant areas while total-surface-bearing concepts spread force broadly to reduce peak pressures. Even distribution protects sensitive anatomy such as the tibial crest and distal tibia.

Question 2Prosthetics

A patient with a transfemoral amputation is being fitted with a quadrilateral socket. Which anatomic structure is intended to bear the primary ischial seating load?

  1. Ischial tuberosity Correct answer.
  2. Greater trochanter
  3. Pubic symphysis
  4. Sacrum

Explanation

The quadrilateral socket uses an ischial seat so the ischial tuberosity bears weight on the posterior brim. This offloads the sensitive femoral triangle and adductor region.

Question 3Prosthetics

Which suspension method relies on a silicone liner with a distal umbrella and pin that locks into a shuttle lock?

  1. Suction suspension
  2. Pin-and-lock suspension Correct answer.
  3. Vacuum-assisted suspension
  4. Cuff suspension

Explanation

Pin-and-lock systems use a distal pin on the liner engaging a shuttle lock in the socket. This provides mechanical suspension and consistent limb seating.

Question 4Prosthetics

Which foot component is best suited to store and return energy during running in a young active amputee?

  1. Solid ankle cushion heel (SACH) foot
  2. Single-axis foot
  3. Carbon-fiber energy-storing foot Correct answer.
  4. Flexible keel foot

Explanation

Carbon-fiber energy-storing feet deflect under load and return energy during push-off, benefiting high-activity users. Simpler feet do not store and return energy efficiently.

Question 5Prosthetics

Which outcome measure is specifically designed to assess balance confidence in lower-limb prosthesis users?

  1. Activities-specific Balance Confidence (ABC) scale Correct answer.
  2. Six-Minute Walk Test
  3. Timed Up and Go
  4. Two-Minute Walk Test

Explanation

The ABC scale is a self-report questionnaire measuring confidence in performing activities without losing balance. The walk tests measure physical performance rather than balance confidence.

Question 6Prosthetics

What is the primary purpose of a prosthetic liner in a lower-limb prosthesis?

  1. Provide terminal device function
  2. Replace the need for alignment
  3. Increase socket rigidity
  4. Protect residual limb skin and assist suspension Correct answer.

Explanation

Liners cushion the residual limb, manage shear and pressure, and often interface with suspension mechanisms. They do not provide structural rigidity or alignment.

Question 7Prosthetics

In upper-limb prosthetics, which control scheme uses remaining muscle contraction to trigger a powered hand?

  1. Myoelectric control Correct answer.
  2. Passive cosmetic control
  3. Switch-controlled terminal device
  4. Body-powered cable control

Explanation

Myoelectric prostheses detect electrical activity from residual muscles via surface electrodes to control motors. Cable and passive systems use mechanical or no active control.

Question 8Prosthetics

Which gait deviation is characterized by excessive knee flexion during stance in a transtibial prosthesis user?

  1. Knee buckling Correct answer.
  2. Circumduction
  3. Lateral trunk bending
  4. Vaulting

Explanation

Knee buckling is excessive flexion of the prosthetic knee during weight acceptance in stance. It may result from poor alignment, weak quadriceps, or socket discomfort.

Question 9Prosthetics

A transtibial prosthesis is aligned with excessive socket flexion. Which gait deviation is most likely to result?

  1. Knee hyperextension during stance
  2. Excessive knee flexion at heel strike Correct answer.
  3. Decreased step length on the sound side
  4. Excessive prosthetic toe-out

Explanation

Excessive socket flexion displaces the body anteriorly relative to the foot, prompting increased knee flexion at initial contact. Alignment adjustments can reduce this tendency.

Question 10Prosthetics

Which transtibial socket modification is used to accommodate a prominent distal tibial prominence?

  1. Relief over the distal tibia Correct answer.
  2. Increased distal end bearing
  3. Tightened medial wall
  4. Extended posterior brim

Explanation

A relief or recess over bony prominences reduces focal pressure on sensitive areas such as the distal tibia. Distal end bearing is avoided over such prominences.

Question 11Prosthetics

In transfemoral socket design, the ischial containment (MAS) socket primarily aims to achieve which effect compared with the quadrilateral socket?

  1. Elimination of the ischial seat
  2. Reduced need for suspension
  3. Increased anterior wall height
  4. Medial-lateral containment of the ischium and femur Correct answer.

Explanation

Ischial containment sockets grasp the ischium medially and laterally to improve femoral control and stability. This contrasts with the flat posterior ischial seat of quadrilateral designs.

Question 12Prosthetics

A patient reports pistoning of the residual limb within the socket during walking. Which cause should be evaluated first?

  1. Incorrect terminal device selection
  2. Overly long prosthetic toe lever
  3. Inadequate suspension or socket volume mismatch Correct answer.
  4. Excessive prosthetic foot stiffness

Explanation

Pistoning indicates the limb is moving within the socket, typically from insufficient suspension or a volume change. Evaluating fit and suspension addresses the root cause.

Question 13Prosthetics

Which knee unit feature allows a transfemoral prosthesis to resist knee flexion during stance while permitting swing-phase flexion?

  1. Friction swing control only
  2. Manual knee lock only
  3. Extension assist spring only
  4. Weight-activated stance control Correct answer.

Explanation

Weight-activated stance control engages a brake or geometric lock under load to prevent buckling. During swing, the mechanism releases to allow knee flexion.

Question 14Prosthetics

A microprocessor knee is most likely to benefit which patient profile?

  1. A patient with a fixed knee contracture
  2. A patient who only stands for transfers
  3. A community ambulator with variable cadence and fall concerns Correct answer.
  4. A bed-bound patient with no ambulation goals

Explanation

Microprocessor knees adjust resistance to cadence and terrain, improving safety for variable-activity ambulators. They offer little benefit to non-ambulatory users.

Question 15Prosthetics

Which prosthetic wrist unit allows powered rotation of the terminal device in an upper-limb prosthesis?

  1. Quick-disconnect wrist
  2. Flexion wrist unit
  3. Friction wrist unit
  4. Electric wrist rotator Correct answer.

Explanation

An electric wrist rotator uses a motor to provide powered pronation and supination of the terminal device. Passive units rely on manual positioning.

Question 16Prosthetics

Which casting or measurement principle helps ensure proper transtibial socket volume during fabrication?

  1. Casting with the knee fully extended and unloaded
  2. Capturing the limb in a functional, loaded position Correct answer.
  3. Ignoring soft tissue consistency
  4. Applying maximal distal traction during casting

Explanation

Casting with the limb in a functional position captures soft tissue shape under load, improving fit. Unloaded or traction-based casts distort limb volume.

Question 17Prosthetics

Which gait deviation is suggested by excessive vertical oscillation of the body during walking with a prosthesis?

  1. Foot slap
  2. Vaulting Correct answer.
  3. Wide base of support
  4. Knee buckling

Explanation

Vaulting raises the body onto the sound toe to clear a long or stiff prosthesis, increasing vertical oscillation. It often signals a prosthesis that is too long or has inadequate knee flexion.

Question 18Prosthetics

A patient with a transfemoral amputation demonstrates excessive lateral trunk bending toward the prosthetic side. Which cause is most likely?

  1. Excessive knee friction
  2. Excessive prosthetic length
  3. Short prosthetic length or weak hip abductors Correct answer.
  4. Stiff heel cushion

Explanation

Lateral trunk bending toward the prosthesis often compensates for a short prosthesis or hip abductor weakness. The trunk lean helps clear the limb or stabilize the pelvis.

Question 19Prosthetics

Which component is used in a body-powered upper-limb prosthesis to transmit force from shoulder motion to the terminal device?

  1. Servo motor
  2. Linear actuator
  3. Bowden cable Correct answer.
  4. Myoelectric electrode

Explanation

A Bowden cable transmits tension from a harness driven by shoulder and scapular motion to operate the terminal device. Electronic components are used in powered systems.

Question 20Prosthetics

Which factor most directly determines the choice between endoskeletal and exoskeletal prosthetic construction?

  1. Terminal device color
  2. Patient's blood type
  3. Socket liner brand
  4. Need for alignment adjustability and cosmetic finishing Correct answer.

Explanation

Endoskeletal systems use a modular pylon and allow alignment changes with a cosmetic cover, while exoskeletal systems are rigid shells. Clinical needs for adjustability and cosmesis guide the choice.

Question 21Prosthetics

A patient with a Syme amputation typically requires which prosthetic design feature?

  1. A transfemoral ischial containment socket
  2. A socket that accommodates the long residual limb with distal load bearing and a posterior opening Correct answer.
  3. A wrist disarticulation unit
  4. A knee disarticulation knee joint

Explanation

Syme amputations leave a long, bulbous residual limb that can tolerate distal weight bearing. The socket often uses a posterior or medial opening to accommodate the distal bulbosity.

Question 22Prosthetics

Which biomechanical principle explains why a prosthetic foot with a longer toe lever increases resistance to toe-off?

  1. Increased hip abduction
  2. Increased external moment arm about the ankle Correct answer.
  3. Decreased socket volume
  4. Reduced knee flexion moment

Explanation

A longer toe lever lengthens the moment arm from the ankle, increasing the torque required for rollover. This can alter push-off mechanics and knee loading.

Question 23Prosthetics

In ischial containment socket theory, the socket must contain the ischium while allowing which structure to remain free of excessive pressure?

  1. The patella
  2. The greater trochanter
  3. The sacrum
  4. The femoral triangle and neurovascular bundle Correct answer.

Explanation

Ischial containment designs must avoid compressing the femoral triangle, where major neurovascular structures run. Proper containment balances medial-lateral control with protection of these tissues.

Question 24Prosthetics

A microprocessor knee that uses hydraulic resistance with sensors detecting stance and swing is best described as having which control characteristic?

  1. Real-time phase-dependent resistance adjustment Correct answer.
  2. Fixed mechanical friction only
  3. Passive extension assist only
  4. Manual lock engagement

Explanation

Microprocessor knees use sensors to detect gait phase and adjust hydraulic resistance in real time. This provides stance stability and swing control tailored to cadence.

Question 25Prosthetics

Which outcome is most appropriate to quantify functional mobility change after fitting a new transfemoral prosthesis in a community ambulator?

  1. Change in the Prosthetic Limb Users Survey of Mobility (PLUS-M) score Correct answer.
  2. Change in socket liner thickness
  3. Change in terminal device color
  4. Change in residual limb circumference alone

Explanation

PLUS-M is a validated patient-reported measure of mobility for people with lower-limb loss. It captures perceived functional mobility change relevant to prosthetic fitting.

Question 26Prosthetics

Which material is most commonly used for the flexible inner socket in a transtibial prosthesis?

  1. Thermoplastic elastomer Correct answer.
  2. Stainless steel
  3. Aluminum
  4. Carbon fiber

Explanation

Flexible inner sockets are typically made from thermoplastic elastomers such as silicone or urethane to provide comfort and conform to the residual limb. Carbon fiber, aluminum, and stainless steel are rigid materials used for structural components, not flexible inner sockets.

Question 27Prosthetics

Which of the following is a primary function of a prosthetic foot's heel wedge?

  1. To align the foot in dorsiflexion
  2. To increase forefoot stiffness
  3. To absorb impact at heel strike Correct answer.
  4. To provide toe-off resistance

Explanation

The heel wedge compresses during heel strike to absorb impact forces and simulate ankle plantarflexion. Toe-off resistance is primarily provided by the toe lever and forefoot stiffness, not the heel wedge.

Question 28Prosthetics

Which suspension method relies on a silicone liner with a distal pin that locks into a shuttle lock?

  1. Pin lock suspension Correct answer.
  2. Cuff suspension
  3. Vacuum-assisted suspension
  4. Suction suspension

Explanation

Pin lock suspension uses a distal pin on the liner that engages a shuttle lock in the socket bottom to secure the prosthesis. Suction and vacuum suspension rely on negative pressure, while cuff suspension uses a strap above the knee.

Question 29Prosthetics

Which of the following is a typical advantage of an endoskeletal prosthesis over an exoskeletal one?

  1. More natural cosmetic appearance without a cover
  2. Easier alignment adjustments Correct answer.
  3. Greater durability in wet environments
  4. Lower initial cost

Explanation

Endoskeletal prostheses have modular components that allow alignment changes by adjusting adapters, making them easier to realign. Exoskeletal prostheses are often less expensive and more durable but harder to adjust.

Question 30Prosthetics

Which terminal device is best suited for activities requiring precise grasping of small objects?

  1. Hook Correct answer.
  2. Passive hand
  3. Greifer
  4. Mechanical hand

Explanation

Hooks provide opposed, narrow tips that allow precise prehension of small objects. Hands and Greifers are bulkier and less suited for fine grasping.

Question 31Prosthetics

Which of the following is a common cause of skin breakdown under a prosthetic socket?

  1. Proper socket fit
  2. Excessive local pressure Correct answer.
  3. Adequate suspension
  4. Regular skin inspection

Explanation

Excessive local pressure from a poorly fitting socket can cause ischemia and skin breakdown. Adequate suspension, proper fit, and regular inspection help prevent skin problems.

Question 32Prosthetics

Which of the following is a typical feature of a microprocessor-controlled prosthetic knee?

  1. Fixed friction resistance
  2. Adjustable stance and swing resistance Correct answer.
  3. Manual lock for stance
  4. Mechanical extension aid only

Explanation

Microprocessor knees use sensors and algorithms to adjust stance and swing resistance in real time. Fixed friction, manual locks, and simple extension aids are features of non-microprocessor knees.

Question 33Prosthetics

Which of the following is a primary goal of prosthetic training for a new amputee?

  1. Maximizing prosthetic weight
  2. Relying solely on the prosthesis for balance
  3. Avoiding all physical activity
  4. Achieving safe and efficient mobility Correct answer.

Explanation

Prosthetic training aims to help the patient use the prosthesis safely and efficiently in daily activities. Increasing weight, avoiding activity, or relying solely on the prosthesis are not goals.

Question 34Prosthetics

A patient with a transfemoral amputation is being fitted with a new prosthesis. Which outcome measure is most appropriate to assess functional mobility?

  1. Timed Up and Go (TUG) Correct answer.
  2. Visual analog scale for pain
  3. Manual muscle test of the residual limb
  4. Goniometric measurement of knee flexion

Explanation

The Timed Up and Go is a performance-based measure of functional mobility that includes walking and transfers. Pain scales, manual muscle tests, and range-of-motion measurements do not directly quantify mobility.

Question 35Prosthetics

During dynamic alignment of a transtibial prosthesis, the patient demonstrates excessive knee flexion at initial contact. Which adjustment is most likely to correct this?

  1. Move the foot anteriorly Correct answer.
  2. Increase heel stiffness
  3. Move the foot posteriorly
  4. Increase socket flexion

Explanation

Moving the foot anteriorly shifts the ground reaction force anteriorly, which reduces the external knee flexion moment at initial contact. Posterior foot placement or increased socket flexion would worsen knee flexion.

Question 36Prosthetics

A patient with a transradial amputation is being considered for a myoelectric prosthesis. Which factor is most critical for successful use?

  1. Cosmetic appearance
  2. Sufficient and controllable muscle signals Correct answer.
  3. Presence of a long residual limb
  4. Lightweight terminal device

Explanation

Myoelectric prostheses require reliable electromyographic signals from residual muscles to control the hand. While limb length and component weight are relevant, signal quality is essential.

Question 37Prosthetics

Which of the following best describes the purpose of a prosthetic sock in transtibial prosthetic management?

  1. To replace a liner
  2. To increase socket rigidity
  3. To provide suspension
  4. To accommodate residual limb volume changes Correct answer.

Explanation

Prosthetic socks are added or removed to accommodate fluctuations in residual limb volume, ensuring a consistent fit. They do not provide primary suspension or structural rigidity.

Question 38Prosthetics

A patient with a transfemoral prosthesis exhibits excessive heel rise during swing phase. Which component adjustment is most appropriate?

  1. Decrease knee friction
  2. Increase knee friction
  3. Move the knee unit anteriorly
  4. Increase knee extension aid Correct answer.

Explanation

Excessive heel rise in swing indicates insufficient knee extension assistance; increasing the extension aid helps the knee extend more fully before initial contact. Decreasing friction would worsen heel rise, and moving the knee anteriorly affects stance stability.

Question 39Prosthetics

Which of the following is a key consideration when selecting a prosthetic foot for a patient who walks on uneven terrain?

  1. Multi-axial ankle motion Correct answer.
  2. High heel height
  3. Low energy return
  4. Rigid forefoot

Explanation

Multi-axial feet allow inversion/eversion and rotation, which help accommodate uneven surfaces. High heel height, rigid forefoot, and low energy return are not advantageous for uneven terrain.

Question 40Prosthetics

A patient with a bilateral transtibial amputation is being fitted with prostheses. Which gait characteristic is most likely to be observed?

  1. Wide base of support Correct answer.
  2. Short step length
  3. Increased cadence
  4. Decreased energy expenditure

Explanation

Bilateral amputees often use a wide base of support to enhance stability. Cadence is typically reduced, energy expenditure is increased, and step length may be shortened but wide base is a hallmark.

Question 41Prosthetics

Which of the following is a common cause of prosthetic knee instability during stance in a transfemoral prosthesis?

  1. Excessive socket flexion Correct answer.
  2. Too much extension aid
  3. Posterior displacement of the foot
  4. Insufficient knee friction

Explanation

Excessive socket flexion places the ground reaction force anterior to the knee, creating a flexion moment that can cause knee buckling. Insufficient friction and extension aid mainly affect swing phase.

Question 42Prosthetics

Which of the following is an advantage of a suction suspension system for a transtibial prosthesis?

  1. Improved proprioception
  2. Ease of donning for patients with limited hand function
  3. Reduced pistoning Correct answer.
  4. Lower cost compared to pin lock

Explanation

Suction suspension creates a secure hold that minimizes vertical movement (pistoning) of the limb in the socket. It can be difficult to don for patients with limited dexterity and may be more expensive than pin systems.

Question 43Prosthetics

A patient with a transfemoral amputation reports that the prosthesis feels too heavy and energy expenditure is high. Which component change is most likely to improve efficiency?

  1. Use a rigid belt suspension
  2. Switch to a lighter foot Correct answer.
  3. Increase socket size
  4. Add a heavier knee unit

Explanation

Reducing distal weight, such as with a lighter foot, decreases the energy required to swing the limb and improves efficiency. Increasing socket size or adding weight would worsen the problem.

Question 44Prosthetics

Which of the following best describes the role of the prosthetic team in the rehabilitation of an amputee?

  1. Interdisciplinary collaboration Correct answer.
  2. Patient-directed without professional input
  3. Physician-only decision making
  4. Prosthetist-only care

Explanation

Optimal amputee rehabilitation requires collaboration among physicians, prosthetists, therapists, nurses, and the patient. Single-profession or patient-only approaches are less effective.

Question 45Prosthetics

A patient with a transtibial prosthesis complains of anterior distal residual limb pain. Which socket modification is most likely to relieve this?

  1. Increased socket flexion
  2. Posterior proximal build-up
  3. Tightened suspension
  4. Anterior distal relief Correct answer.

Explanation

Anterior distal pain often results from pressure over the distal tibia; adding relief (a recess) in that area reduces focal pressure. Posterior build-up or increased flexion would not address anterior distal pressure.

Question 46Prosthetics

Which of the following is a characteristic of a patellar tendon-bearing (PTB) socket design?

  1. Open distal end
  2. Load bearing on the patellar tendon Correct answer.
  3. Total contact with the distal tibia
  4. Ischial weight bearing

Explanation

The PTB socket is designed to bear weight on the patellar tendon and other pressure-tolerant areas while relieving pressure on the distal tibia. It is a total-contact design and does not use ischial weight bearing.

Question 47Prosthetics

A patient with a transfemoral prosthesis demonstrates excessive lateral trunk bending toward the prosthetic side during stance. Which of the following is the most likely cause?

  1. Prosthetic limb too short Correct answer.
  2. Excessive knee friction
  3. Prosthetic limb too long
  4. Weak hip abductors on the sound side

Explanation

Lateral trunk bending toward the prosthetic side is a common compensation for a prosthesis that is too short, as the patient tries to reach the ground. A limb that is too long would cause vaulting or circumduction.

Question 48Prosthetics

In upper-limb prosthetics, which of the following best describes the concept of extended physiological proprioception (EPP)?

  1. The user relies on vision to control the prosthesis
  2. The user senses force and position through the prosthesis Correct answer.
  3. The prosthesis moves automatically without user input
  4. The prosthesis provides sensory feedback via electrodes

Explanation

EPP refers to the user's ability to perceive the position and force of the terminal device through the body's own proprioceptive mechanisms, often achieved with body-powered systems. It does not involve automatic movement or electrical feedback.

Question 49Prosthetics

Which of the following is a potential disadvantage of using a vacuum-assisted suspension system?

  1. Higher energy expenditure
  2. Increased pistoning
  3. Risk of skin irritation from negative pressure Correct answer.
  4. Difficulty in maintaining suction

Explanation

Vacuum-assisted suspension can cause skin irritation or breakdown if negative pressure is excessive or the seal is poor. It is designed to reduce pistoning and maintain suction, not increase it.

Question 50Prosthetics

A patient with a transfemoral amputation using a microprocessor knee reports stumbling. Which feature of the microprocessor knee is most likely to reduce the risk of falls?

  1. Fixed knee friction
  2. Manual lock
  3. Swing phase extension
  4. Stance flexion damping Correct answer.

Explanation

Microprocessor knees can detect a stumble and increase stance flexion damping to prevent knee collapse and allow recovery. Swing extension and fixed friction do not address stumble recovery.