Understanding prosthetic components and gait analysis is a cornerstone of P&O and rehabilitation. This guide covers the two most clinically relevant foot assemblies (SACH & Jaipur Foot) and analyzes common gait deviations seen in amputees due to prosthetic errors.
1. SACH Foot (Solid Ankle Cushion Heel)
The SACH foot is the simplest, most durable, and widely used non-articulated foot assembly. It has no moving parts.
Structure & Mechanism
- Keel: A rigid internal wooden or plastic core that mimics the bones of the foot.
- Heel Cushion: Made of soft rubber foam. It compresses during Heel Strike to absorb shock and simulate Plantarflexion (lowering the foot to the ground).
- Toe Section: Flexible rubber that allows for hyperextension during Toe Off.
2. Jaipur Foot
Developed in 1968 by Dr. P.K. Sethi and Master Ram Chander, the Jaipur Foot is a revolution in low-cost prosthetics, designed specifically for the Indian lifestyle.
Comparison: SACH vs. Jaipur Foot
| Feature | SACH Foot | Jaipur Foot |
|---|---|---|
| Movement | Limited. Mostly sagittal plane. | Universal movement (allows Inversion/Eversion). |
| Functionality | Walking on flat surfaces. | Allows Squatting, cross-legged sitting, and walking on uneven terrain. |
| Material | Wood keel + Polyurethane foam. | Microcellular rubber (MCR) + Wood blocks + Cosmetic rubber skin. |
| Appearance | Looks like a shoe filler (needs a shoe). | Looks like a natural foot (has toes, can be used barefoot). |
| Waterproof? | Generally No. | Yes (Water-resistant). |
3. Gait Deviations (Prosthetic Causes)
When observing an amputee walk, deviations often indicate an issue with the prosthesis alignment or fit. Below are the two most frequently asked deviations in exams.
A. Vaulting
Definition: The patient rises up on the toe of the sound (non-amputated) leg during the swing phase of the prosthetic leg to help it clear the ground.
Common Causes:- Prosthesis is too long: The leg cannot clear the ground normally.
- Excessive Knee Friction: The prosthetic knee doesn't bend easily, making the leg effectively longer in swing phase.
- Suspension loose: The prosthesis slips down (pistoning), making it longer.
B. Circumduction
Definition: The patient swings the prosthetic leg outward in a semi-circular arc (abduction) during the swing phase instead of moving it straight forward.
Common Causes:- Prosthesis too long: Similar to vaulting, the patient swings it out to clear the floor.
- Locked Knee / Inadequate Knee Flexion: If the knee won't bend, the leg remains long.
- Socket too small/tight: Causing pain, leading the patient to avoid flexing the hip.
- Weak Hip Flexors: Patient uses abductors to swing the leg forward.
Frequently Asked Questions (FAQs)
The SACH foot is generally prescribed for K1 and K2 levels (household ambulators or limited community ambulators) who walk at a fixed cadence.
It allows for squatting (essential for Indian toilets), sitting cross-legged, walking barefoot, and is waterproof (good for working in fields/mud).
If the heel cushion is too soft, the foot reaches "foot flat" too quickly (foot slap), and the knee tends to hyperextend (extension moment) at heel strike.
Exam Quiz: Prosthetics & Gait (10 MCQs)
Test your knowledge. Click the correct option to see the answer and reasoning.
1. What does SACH stand for?
SACH stands for Solid Ankle Cushion Heel. It implies there is no articulation (Solid Ankle) and a compressible heel wedge.
2. In a SACH foot, what mimics the action of the plantarflexors at heel strike?
When the heel strikes the ground, the soft foam compresses. This allows the foot to lower to the floor, simulating plantarflexion without muscle activity.
3. Which gait deviation is characterized by the patient rising on the toe of the sound limb during the prosthetic swing phase?
Vaulting is a compensatory mechanism to increase the height of the sound side to allow a "too long" prosthesis to clear the ground.
4. A patient with a transtibial amputation exhibits "Circumduction". Which of the following is a likely prosthetic cause?
If the prosthesis is too long, the patient cannot swing it through normally without hitting the floor, so they swing it out to the side (Circumduction).
5. The main advantage of the Jaipur Foot over the SACH foot is:
The Jaipur foot is specifically designed with separate keels and flexible rubber to permit the range of motion needed for squatting and sitting on the floor.
6. If the heel cushion of a SACH foot is too hard, what happens at the knee during heel strike?
A hard heel acts like a long lever arm. It does not compress, so it forces the tibia forward quickly, creating a flexion moment that may cause the knee to buckle.
7. Which material is primarily used for the external appearance of the Jaipur Foot?
The Jaipur foot is vulcanized with a cosmetic rubber layer that mimics the color and texture of natural skin, often including toes.
8. "Lateral Trunk Bending" towards the prosthetic side is usually caused by:
If the prosthesis is short, the patient leans sideways to the prosthetic side to reach the ground. It can also be caused by weak hip abductors (Trendelenburg gait).
9. Who is credited with the development of the Jaipur Foot?
Dr. P.K. Sethi (Orthopedic Surgeon) along with Master Ram Chander (Artisan) developed the Jaipur Foot in 1968.
10. Which K-Level represents an amputee who has the ability for variable cadence and community ambulation (e.g., traversing curbs, stairs)?
K3 ambulators can traverse environmental barriers and walk at variable speeds. They typically require Dynamic Response feet (Energy Storing), not SACH feet.
References
- Sethi, P. K., Udawat, M. P., et al. (1978). "Vulcanized rubber foot for lower limb amputees". Prosthetics and Orthotics International.
- Lusardi, M. M., & Jorge, M. (2013). Orthotics and Prosthetics in Rehabilitation. Saunders/Elsevier.
- Atlas of Prosthetics. (2000). American Academy of Orthopaedic Surgeons.
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