Prosthetics: Transradial, Transfemoral, Transtibial, and Transhumeral Types

What Are the Four Types of Prosthetics?

The four primary classifications of prosthetic devices, based on the anatomical level of limb loss, are transradial (below-elbow arm), transfemoral (above-knee leg), transtibial (below-knee leg), and transhumeral (above-elbow arm).

The field of prosthetics represents a remarkable intersection of engineering, biomechanics, and human physiology, offering individuals who have experienced limb loss the opportunity to regain function, mobility, and independence. While prosthetic devices are highly individualized, they are broadly categorized based on the specific anatomical segment they are designed to replace. Understanding these primary classifications is fundamental to appreciating the diverse challenges and innovative solutions within prosthetic design and rehabilitation.

Transradial Prosthetics (Below-Elbow Arm)

Transradial prosthetics are designed for individuals who have undergone an amputation below the elbow but retain the elbow joint. This category of upper-limb prosthetics focuses on restoring the function of the forearm, wrist, and hand.

• Anatomical Focus: These prostheses replace the forearm and hand, utilizing the residual limb's movement at the elbow and often the shoulder to control the device.
• Types of Control:
  • Body-Powered Prosthetics: Operated by body movements (e.g., shoulder harness and cable system) that open and close the terminal device (hook or prosthetic hand). They are durable, lightweight, and provide proprioceptive feedback.
  • Myoelectric Prosthetics: Utilize electrodes placed over specific muscles in the residual limb. When these muscles contract, they generate tiny electrical signals (EMG signals) that are amplified to control motors in the prosthetic hand or wrist, offering more intuitive and aesthetically pleasing function.
  • Passive Prosthetics: Primarily cosmetic, offering no active function but providing balance and a natural appearance.
• Functional Goals: Restoration of grasp, pinch, and manipulation of objects, enhancing bimanual tasks and activities of daily living.

Transfemoral Prosthetics (Above-Knee Leg)

Transfemoral prosthetics are designed for individuals with an amputation above the knee, requiring the prosthesis to replace the entire lower leg, including the knee joint, shank, and foot. This type of prosthesis presents significant challenges due to the loss of the knee's natural articulation and stability.

• Anatomical Focus: Replaces the thigh, knee joint, lower leg, and foot. The prosthetic socket typically encases the residual femur.
• Key Components:
  • Socket: The most critical component, providing the interface between the residual limb and the prosthesis. A well-fitting socket is paramount for comfort, control, and energy transfer.
  • Knee Unit: Mimics the function of the anatomical knee, allowing for flexion, extension, and weight-bearing stability. Modern knee units range from mechanical (single-axis, polycentric) to highly advanced microprocessor-controlled knees (MPKs) that adapt to various terrains and walking speeds.
  • Pylon (Shank): Connects the knee unit to the prosthetic foot, acting as the structural support.
  • Prosthetic Foot: Designed to absorb shock, provide stability, and assist with propulsion during walking. Options vary from solid ankle cushioned heel (SACH) feet to dynamic response feet and specialized running blades.
• Functional Goals: Restoring stable standing, efficient gait, balance, and the ability to navigate varied environments.

Transtibial Prosthetics (Below-Knee Leg)

Transtibial prosthetics are for individuals whose amputation is below the knee but preserves the knee joint. This preservation of the anatomical knee simplifies prosthetic design and often allows for a more natural gait pattern compared to above-knee amputations.

• Anatomical Focus: Replaces the lower leg (tibia and fibula) and the foot, with the prosthesis attaching to the residual limb just below the knee.
• Advantages: The intact knee joint provides natural knee flexion and extension, significantly aiding in balance, gait, and energy efficiency.
• Key Components:
  • Socket: Encases the residual tibia and fibula. Various designs exist, such as patellar tendon bearing (PTB) and total surface bearing (TSB) sockets, all aiming for optimal load distribution and comfort.
  • Suspension System: Methods to hold the prosthesis securely to the residual limb, including sleeves, pins, suction, and vacuum systems.
  • Pylon: Connects the socket to the prosthetic foot.
  • Prosthetic Foot: Similar to transfemoral prosthetics, a wide range of feet are available to match activity levels and functional needs.
• Functional Goals: Facilitating symmetrical gait, efficient ambulation, shock absorption, and participation in a wide range of physical activities.

Transhumeral Prosthetics (Above-Elbow Arm)

Transhumeral prosthetics are for individuals who have undergone an amputation above the elbow, necessitating the replacement of the entire arm from the shoulder down, including the elbow joint, forearm, wrist, and hand. This is a more complex prosthetic challenge than transradial due to the loss of the elbow's natural articulation.

• Anatomical Focus: Replaces the upper arm, elbow joint, forearm, and hand.
• Increased Complexity: The need to replicate both elbow flexion/extension and hand function makes these devices more intricate and challenging to control.
• Types of Control: Similar to transradial prosthetics, transhumeral devices can be:
  • Body-Powered: Utilize shoulder and trunk movements to control both the elbow joint and the terminal device. This requires precise sequencing of movements.
  • Myoelectric: More advanced systems use multiple electrode sites to control independent motors for the elbow and the terminal device, offering more natural and simultaneous movements.
  • Hybrid Systems: Combine body-powered control for one joint (e.g., elbow) and myoelectric control for another (e.g., hand).
• Functional Goals: Restoring the ability to reach, grasp, lift, and manipulate objects across a broader range of motion, crucial for many daily tasks and vocational activities.

Beyond the Four: Important Considerations

While these four categories define the primary types of prosthetics based on amputation level, the actual design, functionality, and success of a prosthetic device depend on several critical factors:

• Socket Design and Fit: The interface between the residual limb and the prosthesis is paramount. A precisely fitted socket minimizes discomfort, prevents skin breakdown, and optimizes control and energy transfer.
• Material Science and Technology: Advances in lightweight, durable materials (e.g., carbon fiber, titanium) and sophisticated electronics (e.g., microprocessors, bionic components) continually enhance prosthetic performance and comfort.
• Rehabilitation and Training: A comprehensive rehabilitation program, including physical and occupational therapy, is crucial. It teaches individuals how to operate their new prosthesis, adapt to changes in their biomechanics, and integrate the device into their daily lives.
• Individualized Needs: Each prosthetic is custom-fabricated and tailored to the individual's specific amputation level, residual limb characteristics, activity level, lifestyle, and personal goals.

Conclusion

The four main types of prosthetics—transradial, transfemoral, transtibial, and transhumeral—represent the fundamental classifications based on the anatomical location of limb loss. Each type presents unique biomechanical challenges and requires specialized design and technological solutions. The ongoing evolution in materials, control systems, and rehabilitation techniques continues to push the boundaries of what prosthetic devices can achieve, empowering individuals to reclaim function, mobility, and a higher quality of life.