Lower Limb Prosthetics

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Lower Limb Prosthetics: Amputation Levels & Basics - Stump Savvy

  • Key Amputation Levels:
    • Transfemoral (AK): Above knee. Length: 25-30 cm from Gr. Trochanter. Adductor magnus preservation vital.
    • Transtibial (BK): Below knee. Most common. Length: 12-17 cm from Med. Tibial Plateau. Long posterior flap preferred. Knee function key.
    • Syme's: Ankle disarticulation. Heel pad preserved. Good for end-bearing.
  • Ideal Stump Features:
    • Shape: Conical/cylindrical.
    • Skin: Healthy, mobile scar (posterior in BK).
    • Muscles: Stable (myodesis/myoplasty), well-padded.
    • No pain, neuroma, bony spurs.

Amputation levels: Upper and lower limb

⭐ For Transtibial (BK) amputations, a stump length <5 cm is generally inadequate for prosthetic fitting.

Lower Limb Prosthetics: Prosthetic Components - Limb Lego

  • Socket: Interface between residual limb & prosthesis; crucial for comfort & function.
    • Types: Patellar Tendon Bearing (PTB), Total Surface Bearing (TSB).
    • Materials: Thermoplastics, laminated resins.
  • Suspension System: Secures prosthesis to the limb.
    • Methods: Suction (total/partial), Silesian belt, pelvic band, shuttle lock/pin system, vacuum-assisted.
  • Shank (Pylon): Connects socket to ankle/foot; provides structural support & length.
    • Types: Endoskeletal (modular), Exoskeletal (crustacean).
  • Knee Unit (for transfemoral/knee disarticulation):
    • Axes: Single-axis, polycentric.
    • Control: Mechanical friction, hydraulic/pneumatic, microprocessor-controlled (MPC).
  • Ankle-Foot Assembly: Restores foot functions; shock absorption, stability.
    • Types: SACH (Solid Ankle Cushion Heel), SAFE, Dynamic Response (Energy Storing), Microprocessor Ankles.

Labeled lower limb prosthetic components

⭐ The SACH (Solid Ankle Cushion Heel) foot is the most basic and widely prescribed prosthetic foot, especially in resource-limited settings, offering durability but limited multi-axial movement and energy return.

Lower Limb Prosthetics: Gait & Biomechanics - Robo Rhythms

  • Goal: Smooth, symmetrical, energy-efficient gait.
  • Key Biomechanics: Pelvic motion, knee flexion (stance/swing), prosthetic foot/ankle function.
  • Common Gait Deviations (Causes):
    • Transfemoral (AK):
      • Circumduction (Prosthesis long, ↓ knee flexion).
      • Lateral Trunk Bend (Weak abductors, short prosthesis, pain).
      • Vaulting (Prosthesis long, poor suspension).
    • Transtibial (BK):
      • Excessive Knee Flexion - Stance (Stiff heel, socket anterior).
      • Insufficient Knee Flexion - Stance (Soft heel, socket posterior).
      • Foot Slap (Weak PF bumper, poor fit).
  • Energy Cost: ↑ with amputation level.
    • Transtibial: ~20%
    • Transfemoral (Uni): ~70%
    • Bilateral TF: >200%

⭐ > Vaulting (rising on sound limb toe) often indicates the prosthesis is too long or there's insufficient knee flexion during swing.

Prosthetic foot biomechanics during gait

Lower Limb Prosthetics: Prescription & Complications - Fine-Tune & Fixes

  • Prescription Factors: Amputation level (e.g., Transtibial, Transfemoral), K-Levels (K0-K4 for activity/ambulation potential), patient goals, comorbidities.
  • Prosthetic Checkout (Fine-Tuning):
    • Static Assessment: Socket fit (e.g., total surface bearing, ischial containment), prosthesis length, suspension efficacy, standing alignment.
    • Dynamic Assessment: Gait analysis for smoothness, symmetry, and common deviations (e.g., lateral trunk bending, circumduction, vaulting, foot slap). Prosthetic alignment lines and reference points
  • Common Complications & Fixes:
    • Skin Issues (e.g., breakdown, dermatitis, infection): Optimize socket fit, improve hygiene, change interface material, manage infection.
    • Socket Fit Problems (e.g., pistoning, bell-clanging, localized pain): Socket adjustments (padding, flaring), relining, or new socket fabrication.
    • Gait Deviations & Adjustments:
      • Lateral Trunk Bending: Correct prosthesis length, address abductor weakness, adjust medial socket wall.
      • Circumduction: Shorten prosthesis, reduce knee friction/extension assist.

⭐ Pistoning (vertical movement of residual limb within the socket) is a key indicator of poor suspension or significant residual limb volume change, requiring urgent prosthetic review.

  • Phantom Limb Pain vs. Stump Pain: Differentiate for appropriate management (medical, therapy, prosthetic adjustments).

High‑Yield Points - ⚡ Biggest Takeaways

  • Transtibial (BK) prostheses are generally more common and allow better function than transfemoral (AK).
  • The SACH (Solid Ankle Cushion Heel) foot is a basic, durable, and inexpensive option, often used for initial ambulation.
  • Energy-storing feet (e.g., Flex-Foot, carbon fiber) improve gait efficiency and are preferred for active individuals.
  • Socket design is critical: Patellar Tendon Bearing (PTB) for BK and Ischial Containment for AK are key concepts for weight distribution and stability.
  • Phantom limb pain is a frequent and significant post-amputation issue requiring multimodal management, including medication and therapy.
  • Proper prosthetic alignment and socket fit are essential to prevent gait deviations, skin breakdown, and discomfort.
  • Osseointegration offers direct skeletal attachment, an advanced option for select patients with problematic socket wear.

Practice Questions: Lower Limb Prosthetics

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Amputation is often not required in:

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Flashcards: Lower Limb Prosthetics

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_____ due to discomfort and poor appearance is the most common complication of bracing.

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_____ due to discomfort and poor appearance is the most common complication of bracing.

Poor compliance

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