9.2 Upper and Lower Limb Prosthetics

Upper and lower limb prosthetics are game-changers for amputees. These devices replace missing body parts, restoring function and independence. From simple passive limbs to high-tech powered ones, prosthetics come in various types to suit different needs.

Designing prosthetics is a mix of art and science. It involves custom socket fitting, advanced materials, and smart control systems. The goal? To create limbs that feel natural, work well, and improve quality of life for users.

Upper Limb Prosthetics

Types of Upper Limb Prostheses

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• Transradial prostheses replace the forearm and hand, attaching below the elbow joint
  • Commonly used for amputations between the wrist and elbow
  • Allows for retention of natural elbow movement
  • Can include functional hand or hook components
• Transhumeral prostheses replace the entire arm from above the elbow to the hand
  • Used for amputations between the shoulder and elbow
  • Requires artificial elbow joint for arm flexion and extension
  • May include advanced shoulder mechanisms for improved range of motion

Control Mechanisms and Functionality

• Myoelectric control utilizes electrical signals from residual muscles to operate prosthetic components
  • Electrodes placed on the skin detect muscle contractions
  • Signals are amplified and processed to control motors in the prosthesis
  • Allows for more intuitive and natural movement control
• Passive prosthetics provide cosmetic appearance and basic functionality without powered components
  • Typically lighter and require less maintenance
  • Can include manually positioned joints for static positioning
  • Often used for activities requiring minimal dexterity (holding objects)
• Powered prosthetics incorporate motors and batteries to enable active movement of joints and components
  • Provide greater functionality and grip strength
  • Can perform complex movements like individual finger control
  • Require regular charging and maintenance

Lower Limb Prosthetics

Types of Lower Limb Prostheses

• Transtibial prostheses replace the lower leg and foot, attaching below the knee joint
  • Used for amputations between the ankle and knee
  • Retains natural knee function for improved gait
  • Typically includes a prosthetic foot and ankle component
• Transfemoral prostheses replace the entire leg from above the knee to the foot
  • Used for amputations between the hip and knee
  • Requires an artificial knee joint for leg flexion and extension
  • Challenges include maintaining stability during walking and standing

Advanced Lower Limb Prosthetic Technologies

• Microprocessor knees use onboard computers to adjust knee function in real-time
  • Sensors detect changes in walking speed, terrain, and user intent
  • Automatically adjust resistance and swing characteristics
  • Improve stability and reduce the risk of falls
  • Examples include the C-Leg and Genium systems
• Energy storage and return feet utilize flexible materials to store and release energy during gait
  • Carbon fiber blades compress during heel strike and release energy during push-off
  • Improve efficiency and reduce energy expenditure during walking
  • Enhance performance in activities like running and jumping
  • Examples include the Flex-Foot Cheetah used by Paralympic athletes

Prosthetic Design and Fitting

Socket Design and Customization

• Socket design forms the critical interface between the residual limb and prosthesis
  • Custom-molded to fit the unique shape of the residual limb
  • Materials include thermoplastics, carbon fiber, and silicone
  • Must distribute pressure evenly to prevent skin irritation and maintain comfort
  • Advanced techniques like 3D scanning and printing improve fit accuracy
• Suspension systems secure the prosthesis to the residual limb
  • Suction suspension uses negative pressure to hold the prosthesis in place
  • Pin lock systems employ a mechanical pin to attach the liner to the socket
  • Vacuum-assisted suspension actively removes air between the liner and socket
  • Selection depends on user activity level, residual limb condition, and personal preference

Alignment and Optimization

• Prosthetic alignment involves adjusting the position and orientation of components
  • Static alignment performed during initial fitting to establish basic positioning
  • Dynamic alignment fine-tunes the prosthesis based on gait analysis and user feedback
  • Proper alignment improves comfort, reduces energy expenditure, and prevents secondary complications
  • May require multiple sessions to achieve optimal results
• Considerations for alignment include
  • Socket position relative to the knee or elbow axis
  • Foot placement for even weight distribution and natural gait
  • Component rotations to match the contralateral limb
  • Adjustments for leg length discrepancies or other anatomical factors