Prosthetic liners are soft interface components placed between the residual limb and socket to provide cushioning, suspension, skin protection, and improved fit. Two common materials are medical‑grade silicone and thermoplastic elastomer (TPE). Liners may be engineered as locking (pin) liners for mechanical suspension or as cushioning liners focused on pressure distribution and comfort. Selection depends on suspension method, skin condition, activity level, limb shape and volume management needs.
Silicone Liners
- Material & feel: Medical‑grade silicone offers durable, tacky contact, high shear damping and excellent long‑term cushioning. Silicone maintains consistent mechanical properties over temperature and time.
- Typical uses: Preferred for pin/lock systems and many cushion‑type liners; useful when skin protection and reduced friction/shear are priorities.
- Advantages: Superior shock absorption, good adhesion to skin (reduces pistoning), durable, good chemical resistance to oils and sweat.
- Limitations: Heavier than some TPEs; may be more expensive; some users sensitive to silicone formulations (rare).
- Care: Daily washing with mild soap and water; air dry away from heat; avoid oil‑based products; store flat or on a form.
TPE (Thermoplastic Elastomer) Liners
- Material & feel: TPEs mimic rubber-like elasticity, are lighter and often more flexible than silicone, and can be produced with variable shore hardness for tailored cushioning.
- Typical uses: Cushioning liners, volume‑management sleeves, and liners used with suction or elevated vacuum suspension systems.
- Advantages: Lightweight, good elasticity for stretch-fit designs, cost-effective, easy to fabricate in varied durometers.
- Limitations: May absorb more moisture, can oxidize or harden over long time or heat exposure; typically less shear‑damping than silicone.
- Care: Similar cleaning routine as silicone; use desiccant storage for humid climates; monitor for material degradation.
Locking (Pin) Liners
- Purpose: Provide secure mechanical suspension using an integrated distal pin that engages a socket lock (pinlock). Designed to minimize pistoning and provide clear don/doff mechanics.
- Materials: Commonly manufactured in silicone for tackiness and low shear, but also produced in TPE variants for weight or cost considerations.
- Key features: Reinforced distal pin assembly, tapered distal shape for seating, often available in multiple gel thicknesses for cushioning vs. low‑profile fit.
- Indications: Transtibial users seeking reliable mechanical suspension, users with good limb shape and skin suitable for pin systems; helpful where simple, robust donning is required.
- Considerations: Potential distal concentration of load; require regular inspection of pin and lock; manage distal skin health and monitor for traction blisters.
Cushioning Liners
- Purpose: Prioritize pressure distribution, impact absorption, and limb comfort. Often used with suction, vacuum suspension, or over a secondary sleeve.
- Materials: Available in silicone and TPE, in multiple thicknesses and shore hardnesses to match patient needs.
- Key features: Even pressure distribution, enhanced tissue protection, variable thickness zones (e.g., extra distal padding), moisture‑wicking or antimicrobial covers.
- Indications: Users with sensitive or scarred skin, high‑impact ambulators requiring extra shock absorption, volume fluctuation where softer interface aids comfort.
- Considerations: Thicker cushioning alters limb‑to‑socket fit—socket geometry and alignment must be adjusted; durability varies by material and activity level.
Sizing, Fit & Compatibility
- Accurate sizing and gait‑specific fitting are essential—liners affect socket fit and alignment. Choose left/right specific liners when available and match thickness to socket design.
- Compatibility with suspension systems (pinlocks, suction sleeves, elevated vacuum pumps) must be confirmed.
- Many liners come with fabric covers, seals, or distal adapters—ensure accessories match the liner model.
Clinical & Safety Notes
- Conduct skin assessment before selecting liner material and thickness. Avoid use over open wounds unless device and protocol support it.
- Monitor for signs of skin breakdown, excessive moisture, or allergic reaction. Rotate liners and replace per manufacturer guidance or when integrity degrades.
- Document liner lot, size, thickness, and wear patterns for traceability and to guide remakes.
Selection guidance (brief)
- Choose silicone locking liners for secure pin suspension with high shear protection.
- Choose TPE cushioning liners for lighter-weight cushioning, cost sensitivity, or when specific elasticity profiles are desired.
- For vacuum/suction systems or sensitive skin, prefer cushion liners with validated sealing and moisture management features.
Care & Maintenance (summary)
- Clean daily with mild soap and water; rinse thoroughly and air dry.
- Avoid solvents, bleaching agents, and direct heat.
- Inspect regularly for tears, seam separation, or pin wear; replace per wear or manufacturer intervals.
By matching material, thickness, and suspension type to the user’s limb characteristics and functional needs, clinicians can maximize comfort, function, and device longevity.
