SACH Foot (Solid Ankle Cushion Heel)

• Origin: Developed in the USA in the 1950s
• Design: No moving ankle joint - the ankle is solid/fused
• Mechanism: A soft foam/rubber wedge at the heel compresses on heel strike to simulate plantarflexion
• Movement: Plantarflexion only (via heel compression); no true inversion/eversion
• Use: Low to moderate activity; widely used as a basic standard prosthetic foot globally
• Limitation: Cannot squat, walk on uneven ground easily, or wear thong sandals

Madras Foot

• Origin: Developed at the Rehabilitation Institute, Chennai (Madras), India
• Design: Single-axis wooden foot with a pivot ankle joint
• Movement: Allows some plantarflexion and dorsiflexion via the hinge
• Use: Budget prosthetic option; suited for low-activity rural users
• Limitation: No inversion/eversion; not ideal for uneven terrain

Jaipur Foot (Jaipur Limb)

• Origin: Developed in 1968 by Dr. Pramod Karan Sethi and master craftsman Ram Chandra Sharma in Jaipur, India
• Design: Vulcanized rubber construction with a toe separation gap for wearing chappals/thong sandals
• Movement: Multi-axis - allows dorsiflexion, plantarflexion, inversion, AND eversion
• Special features: Rounded heel allows full squatting; can walk on uneven terrain, muddy fields, and go barefoot
• Cost: Extremely low cost (~$45-50), making it accessible in developing countries
• Impact: Over 1.3 million fitted globally; considered one of the best low-cost prosthetic solutions for developing-world conditions

TRANSTIBIAL (Below-Knee) Sockets

1. PTB - Patellar Tendon Bearing

• Weight bearing: Primarily on the patellar tendon bar (the flat area just below the patella)
• Pressure relief areas: Tibial crest, tibial tubercle, fibular head, distal tibia
• Suspension: Usually via supracondylar strap, sleeve, or cuff
• Trim line: Just below the patella proximally
• Key feature: Selective loading - NOT total contact in the traditional sense

2. TSB - Total Surface Bearing

• Weight bearing: Distributed uniformly across the entire residual limb
• Interface: Silicone/gel liner worn against the skin; pin lock or lanyard at the distal end
• Suspension: Pin-lock or suction via the liner
• Key feature: Reduces pistoning, improves proprioception, better for sensitive stumps
• Modern standard: Has largely replaced PTB in high-income settings

3. KBM - Kondylen Bettung Munster (German origin)

• Proximal trim line: Extends above the femoral condyles medially and laterally
• Suspension: Self-suspending - the condyles are captured within the socket walls
• No sleeve needed for suspension
• Key feature: Good for short or fleshy stumps where sleeve suspension fails
• Limitation: Restricts knee flexion slightly due to higher brim

4. Supracondylar Socket

• Proximal trim line: Rises above and encloses the femoral epicondyles
• Suspension: Condylar capture (medial wall is removable/wedge for donning)
• Difference from KBM: More complete condyle enclosure; distinct removable medial wall design
• Key feature: Self-suspending without any external sleeve or strap

5. Supracondylar-Suprapatellar (SC/SP)

• Proximal trim line: Covers both femoral condyles AND the patella
• Suspension: Maximum condylar + patellar capture
• Key feature: Best mediolateral (ML) stability; used for very short transtibial stumps
• Trade-off: Limits full knee flexion; cosmetically bulkier proximally

TRANSFEMORAL (Above-Knee) Sockets

6. Quadrilateral Socket

• Shape: Roughly rectangular when viewed from above
• Weight bearing: Ischial tuberosity rests ON TOP of the posterior brim (outside the socket)
• Walls: Anterior wall is tallest; posterior brim is flat as a shelf for ischium
• Adductor channel: Medial wall has a relief groove for the adductor longus tendon
• Historical: Dominant design from 1950s-1980s; now largely replaced
• Limitation: Tends to cause lateral socket shift; femoral adductors compressed

7. Ischial Containment Socket (IC / CAT-CAM / NSNA)

• Shape: Narrow ML width, more anatomically oval
• Weight bearing: Ischial tuberosity is INSIDE the socket (contained), not resting on top
• Key feature: Medial brim captures the ischium and inferior pubic ramus - creates a true bony lock
• Benefits: Better adductor function, improved gait, less pelvic drop (Trendelenburg)
• Current standard: Preferred design for most transfemoral amputees today

8. MAS Socket - Marlo Anatomical Socket

• Developed by: Marlo Ortiz (prosthetist), Mexico
• Shape: Very low anterior trim line (sub-ischial); high lateral wall
• Weight bearing: Ischium and ramus fully contained; weight through lateral femur and soft tissue
• Key feature: Dramatically improved sitting comfort; allows greater hip flexion
• Use: Active patients; gaining popularity as an alternative to standard IC sockets
• Trade-off: Technically demanding to fabricate; not suitable for all stump shapes

Quick Comparison Table

1. Silicone Liner

• Material: Medical-grade silicone elastomer
• Wall thickness: Typically 3mm, 6mm, or 9mm - uniform throughout
• Inner surface: High-friction texture that grips the skin directly - rolled on inside-out
• Outer surface: Fabric reinforcement layer bonded to silicone for durability
• Suspension: Distal pin-lock mechanism (most common) or lanyard; also used with suction
• Properties:
  • Highest durability of all liner types (12-18 months typical lifespan)
  • Moderate cushioning
  • Excellent suspension via pin
  • May cause sweating due to non-breathable material
• Best for: Active users, stable mature stumps, those needing reliable suspension
• Common brands: Ossur Alpha, Otto Bock 6Y series

2. Gel Liner

• Material: Tri-layer - outer fabric + middle mineral oil/gel core + inner silicone skin contact layer
• Wall thickness: Variable - thicker over bony prominences for targeted cushioning
• Key feature: The gel core provides superior shock absorption and pressure redistribution
• Suspension: Distal pin-lock or locking lanyard
• Properties:
  • Best cushioning of all liner types
  • Ideal for sensitive, scarred, or grafted residual limbs
  • Shorter lifespan than silicone (~6-12 months) - gel can degrade
  • Heavier than silicone
• Best for: Patients with skin breakdown, bony prominences, pain at tibial crest or fibular head, diabetic stumps
• Common brands: Ossur Iceross, Ohio Willow Wood Alpha Hybrid

3. Polyurethane (PUR) Liner

• Material: Polyurethane foam/elastomer matrix
• Wall thickness: Uniform, slightly firmer feel than silicone
• Inner surface: Lower friction than silicone - easier to don, less shear force on skin
• Suspension: Typically lanyard or suction based (often no pin)
• Properties:
  • Lowest friction of the three - reduces skin shear
  • Good for patients with fragile or hypersensitive skin
  • Moderate cushioning
  • More breathable than silicone
  • Moderate durability (~9-12 months)
  • Slightly higher cost
• Best for: Skin-sensitive patients, those with allergies to silicone, high-shear environments
• Common brands: Ottobock Derma series, Streifeneder PUR liners

4. Custom Soft Liner (Pelite / EVA / Foam)

• Material: Expanded polyethylene (Pelite), EVA foam, or closed-cell foam
• Design: Individually fabricated by casting directly from the patient's residual limb
• Structure: Differential thickness - thick padding over bony prominences (tibial crest, fibular head, distal tibia), thin over soft tissue areas
• Suspension: None intrinsic - sits inside a hard socket as an interface layer; suspension comes from the outer hard socket
• Properties:
  • Fully customized to individual anatomy
  • Excellent for irregular stump shapes, prominent bones, or post-surgical stumps
  • Cheap to fabricate
  • Heat-moldable - can be adjusted chairside
  • No pin/suction - dependent on socket fit for suspension
  • Lower durability (needs replacement every few months as stump changes)
• Best for: New amputees with changing stump volume, very bony stumps, low-resource settings
• Common materials: Pelite (standard), Aliplast, PPT foam

Comparison Table

Clinical Selection Guide

• New amputee with changing stump volume → Custom soft liner (easy to modify)
• Mature stump, active user → Silicone pin-lock liner
• Painful bony prominences / skin breakdown → Gel liner
• Skin allergy to silicone / high shear → Polyurethane liner
• Low-resource / developing world → Custom Pelite soft liner

1. Endoskeletal Pylon ("Endo" / Modular)

• Structure: A central load-bearing tube (the pylon) runs through the core, surrounded by a soft foam cosmetic cover and an outer skin-like stocking
• Materials: Pylon tube in aluminium, titanium, or carbon fiber; foam cover in polyurethane; outer cover in nylon/silicone stocking
• How it works: All structural forces pass through the inner tube; the outer foam and stocking are purely cosmetic and bear no load
• Connection: Pyramid adapters (top and bottom) allow modular attachment to socket, knee unit, and foot - each component can be replaced independently
• Advantages:
  • Lightweight
  • Fully modular - easy component changes and alignment adjustments
  • Better cosmetic appearance with cover
  • Dominant design in modern prosthetics
• Disadvantages: Foam cover tears and degrades; less durable cosmetically
• Used in: Most modern transtibial and transfemoral prostheses

2. Exoskeletal Pylon ("Exo" / Crustacean / Conventional)

• Structure: The hard outer shell IS both the structural and cosmetic element - no inner tube, no soft cover
• Materials: Hard laminated fiberglass, carbon fiber, or polyester resin over a carved foam core; or carved wood (historically)
• How it works: Load passes through the rigid outer shell wall, like a crustacean's exoskeleton
• Connection: Integrated - components are built into the shell, not modular
• Advantages:
  • Extremely durable outer surface - resists abrasion, mud, water
  • No cosmetic cover to replace
  • Better suited for heavy labor and harsh environments
• Disadvantages:
  • Heavy
  • Cannot easily adjust alignment after fabrication
  • Difficult to repair or upgrade components
  • Poor cosmesis once worn
• Used in: Developing world settings (Jaipur limb is partly exo-style), heavy-duty work environments, pediatric prostheses (durable for active children)

3. Standard Rigid Pylon

• Structure: A straight, rigid metallic or carbon fiber tube with no energy-storing or shock-absorbing properties
• Materials: Aluminium (most common, cheapest), titanium (lighter, stronger), carbon fiber (lightest, most expensive)
• Connection: Pyramid adapters at both ends - fully modular
• Properties:
  • Transmits all ground reaction forces directly and rigidly upward into the socket
  • No flex, no energy return, no shock absorption
  • Simple, cheap, reliable
• Advantages: Low cost, easy to source and replace, widely compatible
• Disadvantages: Higher impact forces transmitted to stump and residual joints; no dynamic benefit
• Used in: Budget prostheses, low-activity users (K1-K2 ambulators), developing world

4. Dynamic / Energy-Storing Pylon

• Structure: A carbon fiber pylon with a curved or tapered profile designed to flex under load and rebound on push-off
• Materials: Woven or unidirectional carbon fiber composite
• How it works: The pylon deflects (bends slightly) during stance phase, storing elastic energy, then releases it during late stance/push-off - similar in concept to a carbon fiber running blade
• Key zones: A defined "dynamic flex zone" in the mid-section where controlled bending occurs
• Advantages:
  • Reduces peak impact forces on the stump and proximal joints
  • Returns energy for more efficient gait
  • Reduces metabolic cost of walking
  • Lighter than metal pylons
• Disadvantages: Higher cost; not suitable for very heavy users (may fatigue/fracture)
• Used in: Active users (K3-K4), sports prosthetics, running prostheses, young active amputees
• Examples: Ottobock Taleo, Ossur Flex-Run concept pylons

5. Telescopic Pylon (Shock-Absorbing / Length-Adjusting)

• Structure: Two concentric tubes - an outer tube and an inner sliding tube - that can compress axially
• Internal mechanism: Contains a spring, elastomer bumper, or hydraulic element that resists compression and then rebounds
• Two functions:
  1. Shock absorption: Vertical compression during heel strike reduces impact forces
  2. Length adjustment: Some versions allow manual length setting for height fine-tuning
• Advantages:
  • Significant reduction in vertical impact forces - protects stump, hip, and spine
  • Improves comfort on stairs, ramps, uneven ground
  • Reduces socket pistoning
  • Some allow rotational (torsional) accommodation as well
• Disadvantages: Heavier than standard pylons; adds a potential failure point; more expensive
• Used in: Active users with back/hip pain, bilateral amputees, patients with osteoporosis or sensitive stumps, off-road/outdoor users
• Examples: Ottobock Torsion Adapter, Fillauer ShockMaster, College Park Tru-Step

Quick Comparison Table

1. Supracondylar Suspension

• Mechanism: The socket's proximal trim line extends above the femoral medial and lateral epicondyles, physically capturing the bony condyles within the socket walls
• Key feature: A removable medial wedge is taken out to allow the stump to slide in, then reinserted to lock the condyles inside
• No liner or sleeve needed for suspension
• How it holds: Bony interlock - the condyles are wider than the socket opening at rest, creating a mechanical lock
• Advantages:
  • Simple and reliable
  • No external components to wear out
  • Good for short stumps or patients who struggle with sleeves
• Disadvantages: Slightly limits knee flexion; bulkier socket proximally; not suitable for obese or very fleshy thighs where condyles are not palpable
• Best for: Short-to-medium transtibial stumps, low-to-moderate activity

2. Supracondylar-Suprapatellar (SC/SP) Suspension

• Mechanism: Extends the supracondylar principle further - the trim line also rises anteriorly to enclose the patella
• Three-point bony capture: Medial condyle + lateral condyle + patella all enclosed
• Provides maximum suspension security of all purely bony/mechanical suspension designs
• Advantages:
  • Strongest bony suspension
  • Best mediolateral stability - useful for very short stumps
  • No external components
• Disadvantages:
  • Most restrictive - limits knee flexion significantly (cannot fully flex knee with patella enclosed)
  • Cosmetically bulkier
  • Difficult to don with limited hand dexterity
• Best for: Very short transtibial stumps, patients with weak quadriceps needing anterior stability

3. Sleeve Suspension

• Mechanism: A stretchy silicone or neoprene sleeve is rolled over the outside of the socket and up 6-8 cm onto the bare thigh skin above the socket brim
• How it holds: The sleeve forms an airtight friction seal between the socket brim and the thigh skin - negative pressure builds during swing phase, resisting pull-off
• No liner pin or pump needed
• Advantages:
  • Simple to use
  • Inexpensive
  • Works with almost any liner or socket
  • Good suspension for moderate activity
• Disadvantages:
  • Sleeve degrades and tears (replace every 3-6 months)
  • Rolls down in hot/sweaty conditions
  • Restricts knee flexion slightly if too tight
  • Not suitable for very active users (pistoning occurs during running)
• Best for: K2-K3 users, elderly patients, patients with skin sensitivity to pin mechanisms

4. Pin Locking Suspension

• Mechanism: The silicone or gel liner has a threaded metal pin protruding from its distal tip. As the patient pushes the stump into the socket, the pin engages a ratchet lock mechanism at the socket base - an audible click confirms engagement
• Release: A push-button on the side of the socket disengages the ratchet to remove the prosthesis
• How it holds: Mechanical positive lock - pin physically locked into ratchet; cannot pull out without pressing release button
• Advantages:
  • Highly secure and reliable
  • Audible/tactile confirmation of donning
  • Simple mechanism - low maintenance
  • Most widely used suspension system globally
• Disadvantages:
  • Pin can cause distal end-bearing pressure if stump is very sensitive
  • If patient gains/loses volume, pin may not engage fully
  • Pistoning still occurs between the liner and the skin (not between socket and liner)
• Best for: Most transtibial amputees, K2-K4 activity levels

5. Lanyard Suspension

• Mechanism: Instead of a metal pin, a cord (lanyard) is attached to the distal tip of the liner. The lanyard threads through a small hole at the base of the socket and is then secured to a Velcro strap or buckle on the outer socket wall - tension in the cord prevents the liner (and stump) from pulling out
• How it holds: Tensile force through the cord - pulling the liner distally is resisted by the anchored cord
• Advantages:
  • No metal pin - better for distal-sensitive stumps
  • Allows some distal end relief while still suspending
  • Cheap and simple
  • Works well with polyurethane liners (which often don't have pin attachments)
• Disadvantages:
  • Less secure than pin lock - cord can slip or loosen
  • Lanyard can fray or break
  • Slightly more pistoning than pin lock
  • Requires manual tightening/adjustment
• Best for: Patients with distal stump sensitivity, hypersensitive scar tissue, or those using polyurethane liners

6. Elevated Vacuum Suspension (EVS)

• Mechanism: A battery-powered electric vacuum pump (worn on the prosthesis) continuously draws air out of the sealed space between the liner exterior and the socket interior wall, maintaining a defined negative pressure (typically -50 to -80 mmHg) throughout the gait cycle
• Components: Pump unit, sensor, tubing, one-way valve, sealed socket
• How it holds: Atmospheric pressure difference - the higher external air pressure pushes the liner-covered stump into the socket; the pump removes any air that leaks in
• Advantages:
  • Near-zero pistoning - the gold standard for suspension security
  • Dramatically improved proprioception and ground feel
  • Reduces residual limb volume fluctuation (negative pressure maintains limb shape)
  • Better gait symmetry and energy efficiency
  • Reduces skin breakdown from shear
• Disadvantages:
  • Most expensive suspension system
  • Requires battery charging
  • Heavier (pump unit adds weight)
  • More complex maintenance
  • Pump failure = loss of suspension
• Best for: K3-K4 highly active users, athletes, bilateral amputees, patients with significant volume fluctuation

Comparison Table