Orthoses and Prosthetics
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Direct answer
Orthoses are external devices that support, align or control a body part, whereas prostheses replace a missing part. The ankle-foot orthosis (AFO) controls foot drop, the knee-ankle-foot orthosis (KAFO) controls both knee and ankle, and the Boston brace is a thoraco-lumbo-sacral orthosis used for scoliosis in growing patients. The SACH foot is a simple, low-cost prosthetic foot with a solid ankle.
What you must remember
- Caliper: a metal-upright device with cuffs and a joint or lock; the long leg caliper reaches the thigh to control the knee, and the short leg caliper stops below the knee.
- AFO: controls the ankle and foot, most often for foot drop from common peroneal nerve palsy or poliomyelitis, with a plastic or metal shell.
- KAFO: controls the knee as well as the ankle, used when quadriceps power is inadequate to hold the knee in extension.
- Boston brace: a rigid thoraco-lumbo-sacral orthosis that aims to prevent curve progression in skeletally immature patients with moderate idiopathic scoliosis.
- SACH foot: a solid ankle cushion heel prosthesis with no active ankle motion, suited to low-demand users and inexpensive to produce.
- Jaipur foot: a low-cost below-knee prosthesis developed at SMS Hospital, Jaipur, widely used in India and in resource-limited settings.
- Three-point pressure: orthoses control alignment by pressure at three points, and the pressures must be relieved over bony prominences.
A stepwise approach to prescribing an orthosis
Prescription starts from the deficit, and the device is chosen to control the weak or unstable joint, not to replace the function of a whole limb. Examiners usually expect the same logic in the order below.
- Define the deficit: grade the power of each muscle group and note which joints lack control, such as the dorsiflexors, quadriceps or trunk muscles.
- Pick the level of control: foot drop alone calls for an AFO, whereas quadriceps weakness with an unstable knee needs a KAFO or long leg caliper.
- Choose the material: plastic shells are lighter and more cosmetic, while metal calipers are robust for growing children and severe deficits.
- Check the fit: three-point pressure holds the limb in the device, and pressure areas over bony prominences are relieved before the patient leaves the clinic.
- Train and review: gait training follows, and children are reviewed as they grow because uprights, cuffs and braces need adjustment.
Where the exam tries to catch you
Orthosis questions are usually decided by which joint is weak and whether the device controls it or merely supports it.
- Trap: prescribing an AFO for weak quadriceps. Correct: quadriceps weakness needs knee control, so a KAFO or long leg caliper is used.
- Trap: using the Boston brace to correct an established adult curve. Correct: it aims to stop progression in growing patients with moderate curves, and it does not correct a fixed deformity.
- Trap: expecting the SACH foot to allow active ankle movement. Correct: it has a solid ankle with no active motion, which suits low-demand users.
Frequently asked questions
Which orthosis is used for foot drop?
The ankle-foot orthosis, or AFO, is the standard orthosis for foot drop. It holds the foot in neutral to prevent toe drag during walking. Foot drop most often follows common peroneal nerve palsy or poliomyelitis.
When is a knee-ankle-foot orthosis prescribed?
A knee-ankle-foot orthosis, or KAFO, is prescribed when the knee and ankle both need control, most often because quadriceps power is inadequate to hold the knee in extension. It controls the knee and ankle together. It is heavier than an AFO and is chosen only when the knee cannot be controlled by a simpler device.
What is the Boston brace used for?
The Boston brace is a rigid thoraco-lumbo-sacral orthosis used for scoliosis in growing patients with moderate curves. It aims to prevent progression of the curve during skeletal growth. It does not correct an established curve in an adult.
What is the SACH foot in prosthetics?
The SACH foot is a solid ankle cushion heel prosthetic foot, with a rigid ankle and a cushioned heel. It has no active ankle movement and is inexpensive to produce. It suits patients with low activity demands after amputation.