Advancements in Prosthetics - Inside The Socket - Part 01

Main ideas / concepts conveyed

• Purpose of the “socket”: The socket is the most important part of a lower-extremity prosthesis. It connects the artificial components to the amputee’s residual limb and is custom made to fit the person’s anatomy.

• Socket as a system: The socket is described as an environment made of multiple parts that work together for safe, comfortable suspension and load-bearing. Key components mentioned:

  • Carbon fiber and plastic outer shell
  • A liner that contacts the skin
  • Socks and padding

• Fit changes over time: As the amputee’s body changes (especially residual limb volume), socket fit changes—even for well-made sockets—so patients must monitor comfort and fit.

• Socket design features:

  • Matching the shape of the limb to reduce unwanted movement and manage weight distribution
  • Using a total contact socket approach so weight is shared across more of the residual limb rather than concentrated pressure points
  • Custom top trim/edge shapes (trim lines) that provide support while allowing muscle movement, with differences between above-knee (AK) and below-knee (BK) designs

• Suspension methods: Sockets are held in place using one of four primary methods:

  • Pin lock
  • Lanyard lock
  • Suspension sleeve
  • Suspension belt

• Liners, socks, and skin irritation: The liner acts as the “middle man” between the patient’s skin and the socket, cushioning forces during standing and walking.

  • Common liner materials: silicone, urethane, and thermoplastic elastomer (TPE)
  • Liners may be custom-made or prefabricated, with different thickness/flexibility
  • Liners are also trimmed to match the socket environment

• Patient responsibility and communication: Patients should report issues early; they should not attempt to self-modify liners (e.g., trimming).

• Physical therapy importance: Proper physical therapy is essential for amputee recovery, supported by a home exercise program excerpt and staff physical therapist guidance.

---

Methodology / instructions presented

Socket and fit monitoring (patient learning/behavior)

• Expect fit changes as residual limb shape/size changes over time.
• When residual limb volume decreases (“losing volume”), understand it may be due to:
  • Changes in diet
  • Muscle atrophy
  • Other factors
• Use padding only as directed by prosthetists to relieve pressure points and restore fit:
  • Padding “makes up the difference” but takes up space within the socket
  • Placement varies by time and by person
• Report changes immediately:
  • Any changes in socket fit or comfort
  • Any issues related to liner function or comfort (see liner section below)

Liner use: application steps (to prevent air entrapment and irritation)

• Do not trim liners yourself.
• To apply a liner:
  • Invert the liner (turn it inside out)
  • Roll it onto the residual limb carefully, starting at the end and working upward
  • Aim to ensure no air remains trapped inside the liner
• Avoid pulling it on “like a sock”:
  • Trapped air can cause irritation and skin breakdown

Liner pin-lock alignment (pin lock prostheses)

• If the prosthesis uses a pin lock:
  • The pin is attached to the bottom of the liner
• Alignment is critical:
  • Patients must align the pin correctly when applying the liner
  • If the pin is misaligned, it may be difficult to lock into the docking device
  • Trying to force/angle the pin into the dock can cause:
    • Soreness on the residual limb
    • Pin jamming in the dock, making removal impossible
• Check after liner application:
  • Ensure the pin is straight out from the bottom of the residual limb
  • If not straight: remove the liner and re-apply

BK-specific liner issues to recognize and report

• Pistoning:
  • Feeling the residual limb lift in/out of the socket while walking
  • Depends on the liner type
• Skin stretching inside the liner when weight is placed
  • Depends on the socket/fit
• If either occurs: contact the prosthetist right away to discuss cause and solution.

AK-specific liner handling note

• AK liners have distinct front and back sides that are custom trimmed.
• A black line may mark the front.
• AK patients should always check liner position before rolling it on.

Liner aging / maintenance-related guidance

• Over time, liners may become:
  • Too tight or too loose if residual limb volume changes significantly
  • Damaged due to tearing or abrasions
• If liners become damaged or uncomfortable:
  • Patients should contact a Fourroux prosthetist promptly

---

Speakers / sources featured

• Fourroux (presentation organization)
• Fourroux prosthetists:
  • Analyzing volume loss and fitting/padding
  • Selecting appropriate liners
• Fourroux staff physical therapist:
  • Guiding patients and demonstrating a home exercise program excerpt
• “Our patients” / patients:
  • Referenced as experiencing fit/comfort issues and learning procedures