Orthotics and Prosthetics – Principles and Orthopaedic Applications

Orthotics and prosthetics form an important part of orthopaedic rehabilitation. An orthosis is an externally applied device used to support, align, prevent or correct deformity, protect an injured structure or improve function. A prosthesis is an artificial device that replaces a missing body part, most commonly a limb or part of a limb.

Successful prescription requires more than simply choosing a device. The surgeon must understand the underlying deformity, biomechanics, muscle power, joint range of motion, skin condition, functional demands and rehabilitation potential of the patient.

Orthotic and prosthetic prescription should be goal-directed: the device must solve a specific mechanical or functional problem.

Orthoses may be prescribed to:

• Support a weak limb or joint.
• Maintain alignment.
• Prevent development of deformity.
• Correct a flexible deformity.
• Protect healing bone, tendon or ligament.
• Limit undesirable movement.
• Assist deficient muscle function.
• Redistribute pressure.
• Reduce pain.
• Improve gait efficiency.
• Prevent contracture.
• Improve functional use of the upper limb.

Orthoses act by applying external forces and moments to the body. The fundamental mechanical principles include:

• Three-point pressure system.
• Increasing lever-arm length.
• Maximising contact area to reduce pressure.
• Controlling joint motion.
• Redistributing load.
• Providing external stability.

Many orthoses correct or control deformity using a three-point force system.

One corrective force is applied at the apex of the deformity and two counterforces are applied on the opposite side above and below it.

Examples include braces for:

• Varus-valgus knee control.
• Scoliosis.
• Ankle deformity.
• Hyperextension control.

Orthotic correction is achieved by controlled force systems rather than by simply making the brace rigid.

Pressure is related to the force applied over a given surface area:

Pressure = Force / Area

Increasing the surface area over which a corrective force is applied reduces local pressure and improves comfort.

This principle is particularly important over bony prominences and in patients with impaired sensation.

The turning effect of a force depends on the magnitude of the force and its distance from the axis.

Moment = Force × Perpendicular Distance

Therefore, a longer orthosis can often control a joint with less force than a short orthosis, provided the increased length is practical and tolerated.

Orthoses are commonly named according to the joints or body segments they encompass.

• Thermoplastics.
• Polypropylene.
• Polyethylene.
• Carbon-fibre composites.
• Metal uprights.
• Leather.
• Foam and padding materials.
• Elastic fabrics.

Modern thermoplastics allow lightweight, moulded and relatively cosmetic orthoses. Carbon-fibre devices may provide high stiffness with low weight and can store and release energy during gait.

Foot orthoses may be accommodative, corrective or functional.

Common Components

• Medial longitudinal arch support.
• Metatarsal pad or bar.
• Heel cup.
• Heel wedge.
• Medial or lateral posting.
• Pressure-relieving inserts.

Common Indications

• Flexible flatfoot.
• Pes cavus.
• Plantar fasciitis.
• Metatarsalgia.
• Diabetic pressure redistribution.
• Selected hindfoot alignment disorders.

The AFO is one of the most commonly prescribed lower-limb orthoses. It controls the ankle and indirectly influences the knee during stance and swing.

Common indications include:

• Foot drop.
• Peroneal nerve palsy.
• Stroke.
• Cerebral palsy.
• Spinal cord or neurological disorders.
• Ankle instability.
• Flexible equinus or varus-valgus deformity.

The ankle position changes the direction of the ground-reaction force relative to the knee. Therefore an AFO can indirectly influence knee flexion and extension moments.

Limiting excessive ankle dorsiflexion during stance can move the ground-reaction force anterior to the knee and encourage a knee-extension moment.

This principle is exploited by a ground-reaction AFO, particularly in selected patients with crouch gait.

A KAFO extends from the foot to the thigh and is used when control of the knee as well as the ankle is required.

Indications

• Severe quadriceps weakness.
• Poliomyelitis sequelae.
• Spinal cord injury.
• Neuromuscular disease.
• Marked knee instability.
• Severe coronal-plane deformity requiring support.

• Locked knee joint.
• Drop-lock mechanism.
• Posterior-offset knee joint.
• Free knee joint.
• Stance-control knee mechanism.

A locked knee provides maximum stability but increases the energy required for walking because knee flexion during swing is restricted.

Stance-control systems aim to lock or stabilise the knee during stance and permit flexion during swing.

An HKAFO adds hip and pelvic control to a KAFO.

It may be used in selected patients with severe lower-limb weakness due to:

• Spinal cord injury.
• Spina bifida.
• Severe neuromuscular weakness.

Walking with bilateral HKAFOs can require considerable energy and is therefore more useful for therapeutic standing and selected household or exercise ambulation than for efficient community mobility in many patients.

A reciprocating gait orthosis (RGO) couples the two hip joints so that extension of one hip assists flexion of the opposite hip.

It may be used in selected patients with paraplegia or spina bifida to permit reciprocal stepping with assistive devices.

Knee orthoses may be classified according to purpose.

An unloader brace applies a valgus or varus corrective moment to reduce loading through a painful tibiofemoral compartment.

For example, in symptomatic medial-compartment osteoarthritis with varus alignment, a valgus-producing brace may reduce medial compartment loading.

The effect is usually symptomatic and does not reverse established osteoarthritis.

Spinal orthoses aim to restrict motion, support the trunk, reduce pain, protect healing structures or influence spinal deformity.

Common Categories

• Cervical orthoses.
• Cervicothoracic orthoses.
• Thoracolumbosacral orthoses.
• Lumbosacral orthoses.
• Scoliosis braces.

A TLSO encompasses the thoracic, lumbar and sacral regions and may be used for selected thoracolumbar fractures, postoperative protection and spinal deformity.

A commonly discussed hyperextension brace is the Jewett brace.

It applies three-point pressure with pads over the sternum, pubis and posterior thoracolumbar region to resist excessive spinal flexion.

Bracing in adolescent idiopathic scoliosis is used primarily to reduce the risk of curve progression during skeletal growth, rather than to permanently straighten an established structural curve.

Common Braces

• Boston brace – TLSO.
• Milwaukee brace – CTLSO.
• Other modern custom-moulded TLSO designs.

Bracing success depends strongly on appropriate indication, skeletal growth remaining, curve characteristics and patient adherence.

Upper-limb orthoses may protect healing tissues, prevent deformity, substitute for weak muscles and improve hand function.

Examples

• Wrist cock-up splint.
• Thumb spica.
• Opponens splint.
• Dynamic radial nerve palsy splint.
• Anti-claw splint.
• Elbow extension or flexion splints.
• Static-progressive contracture splints.

Radial nerve palsy can result in loss of wrist, finger and thumb extension.

A dynamic extension splint can:

• Maintain the wrist in a functional position.
• Assist MCP extension.
• Allow active finger flexion.
• Improve grasp and release.
• Prevent flexion contracture.

In ulnar nerve palsy, loss of intrinsic muscle function may produce MCP hyperextension and IP flexion.

An anti-claw orthosis prevents excessive MCP hyperextension, allowing the extensor mechanism to transmit force more effectively to the interphalangeal joints.

This is sometimes called a lumbrical bar splint.

Prosthetic rehabilitation aims to restore functional mobility and independence after limb loss.

Successful prosthetic use depends on:

• Appropriate amputation level.
• Healthy residual limb.
• Good muscle strength.
• Stable joints.
• Appropriate socket design.
• Reliable suspension.
• Proper alignment.
• Patient motivation.
• Cardiopulmonary fitness.
• Effective rehabilitation.

• Painless.
• Well healed.
• Adequate soft-tissue coverage.
• No prominent or unstable bone.
• Good circulation.
• Minimal oedema.
• No active infection.
• Good joint range of motion.
• Adequate residual muscle strength.
• Scar positioned away from major pressure-bearing areas where possible.

The surgeon should consider future prosthetic rehabilitation at the time of amputation.

• Preserve maximum useful limb length without compromising tissue viability.
• Provide durable soft-tissue coverage.
• Contour sharp bony edges.
• Stabilise muscle appropriately.
• Prevent joint contractures.
• Handle nerves carefully to reduce symptomatic neuroma.
• Avoid unnecessary proximal amputation.

Preservation of a functional joint can greatly reduce the energy cost of prosthetic walking.

Myodesis

The muscle or tendon is attached directly to bone, providing stable fixation of the muscle group.

Myoplasty

Opposing muscle groups are sutured to one another over the end of the bone.

These procedures improve residual-limb stability and help provide a controlled soft-tissue envelope.

• Partial foot amputation.
• Syme ankle disarticulation.
• Transtibial amputation.
• Knee disarticulation.
• Transfemoral amputation.
• Hip disarticulation.
• Hemipelvectomy.

In general, energy expenditure increases as the amputation level becomes more proximal.

Preservation of the knee joint makes transtibial amputation substantially more efficient functionally than transfemoral amputation.

Major Components

• Socket.
• Liner or interface.
• Suspension system.
• Pylon or structural frame.
• Prosthetic foot.
• Cosmetic covering when used.

The socket is the most critical interface between the patient and the prosthetic limb.

Its functions include:

• Transfer load between body and prosthesis.
• Provide stability.
• Control the prosthesis.
• Distribute pressure safely.
• Provide comfort.
• Assist suspension.

Poor socket fit is one of the commonest reasons for prosthetic discomfort and skin problems.

The traditional patellar tendon-bearing (PTB) transtibial socket uses selective loading of pressure-tolerant areas while relieving pressure-sensitive structures.

Pressure-Tolerant Areas

• Patellar tendon region.
• Medial tibial flare.
• Lateral shaft region where appropriate.
• Posterior muscular tissues.

Pressure-Sensitive Areas

• Tibial crest.
• Tibial tubercle.
• Fibular head.
• Distal tibia and fibula.
• Common peroneal nerve region.

Modern socket designs frequently use more uniform pressure distribution over the residual limb, often combined with elastomeric or silicone liners.

Total surface-bearing concepts aim to avoid excessive concentration of pressure at a small number of load-bearing areas.

Suspension keeps the prosthesis attached to the residual limb during swing and functional activity.

• Supracondylar suspension.
• Cuff suspension.
• Pin-lock liner.
• Suction suspension.
• Vacuum-assisted suspension.
• Harness systems for selected upper-limb prostheses.

Excessive pistoning between the limb and socket can cause instability, energy loss and skin injury.

SACH stands for Solid Ankle Cushioned Heel.

The ankle itself does not contain a mechanical joint. Heel compression simulates limited plantarflexion after heel strike.

Advantages include simplicity, reliability and low maintenance, but it provides less dynamic energy return than modern energy-storing feet.

A transfemoral prosthesis replaces the missing knee and distal limb.

Major Components

• Socket.
• Suspension system.
• Prosthetic knee.
• Pylon.
• Prosthetic foot.

Because the natural knee is absent, transfemoral prosthetic walking requires greater energy expenditure and more sophisticated control than transtibial prosthetic walking.

Quadrilateral Socket

Traditional design with a relatively narrow anteroposterior dimension and broader mediolateral dimension.

Ischial Containment Socket

Incorporates the ischium and part of the pelvis within the socket contours to improve coronal-plane control and femoral stability.

Microprocessor knees use sensors to monitor gait-related variables and electronically adjust hydraulic or other resistance.

Potential advantages in appropriately selected users include:

• Improved stance-phase stability.
• Better adaptation to variable walking speed.
• Improved negotiation of slopes and stairs with suitable systems.
• Reduced risk of some types of stumble and fall.
• More natural swing-phase control.

Limitations include cost, weight, charging requirements and the need for appropriate patient cognition, activity and training.

Alignment determines the spatial relationship between the socket, joint components and prosthetic foot.

Poor alignment can cause:

• Instability.
• Abnormal gait.
• Excessive pressure within the socket.
• Higher energy expenditure.
• Pain.
• Skin breakdown.

Prosthetic alignment is usually refined dynamically while observing the patient walking.

Gait deviation may arise from poor prosthetic alignment, inadequate socket fit, weakness, contracture, pain or poor gait training.

Contractures can severely interfere with prosthetic alignment and walking.

After Transtibial Amputation

The major concern is knee flexion contracture.

After Transfemoral Amputation

Common tendencies include:

• Hip flexion contracture.
• Hip abduction contracture.
• External rotation deformity.

Early positioning, prone lying where appropriate, physiotherapy and strengthening are therefore essential.

• Wound healing.
• Residual-limb shaping.
• Oedema control.
• Desensitisation.
• Scar mobilisation.
• Prevention of contracture.
• Strengthening.
• Balance training.
• Cardiovascular conditioning.
• Education regarding skin care.

Compression helps reduce postoperative oedema and shape the residual limb for later socket fitting.

Options include:

• Elastic bandaging.
• Shrinker garments.
• Rigid or semi-rigid removable dressings in selected protocols.

Excessive or uneven pressure should be avoided because it can impair circulation and damage skin.

Prosthetic fitting begins when the residual limb has healed sufficiently, oedema is controlled and the patient is medically and functionally ready.

Initial prostheses may require repeated socket modification because residual-limb volume changes during the first months after amputation.

Functional classification systems are used to match prosthetic components to expected mobility. A commonly referenced framework uses activity levels from K0 to K4.

The classification is primarily a functional prescription framework and should not replace individual assessment.

Upper-limb prostheses aim to improve appearance, positioning, grasp and bimanual function.

Major Types

• Passive or cosmetic prosthesis.
• Body-powered prosthesis.
• Externally powered or myoelectric prosthesis.
• Hybrid prosthesis.

A body-powered prosthesis typically uses a harness and cable system. Motion of the shoulder girdle or residual limb generates tension in the cable to operate a terminal device or elbow mechanism.

Advantages

• Relatively durable.
• Lower maintenance than complex electronic systems.
• Provides some mechanical feedback through cable tension.
• Useful for demanding manual activities.

Limitations

• Harness may be uncomfortable.
• Less cosmetic.
• Requires adequate proximal movement.

Myoelectric prostheses use electrical signals generated by contraction of residual muscles to control powered prosthetic components.

Surface electrodes detect muscle activity, which is processed to control movements such as hand opening, closing or powered wrist functions.

Advantages

• Improved cosmetic appearance.
• No conventional control harness required in many designs.
• Potentially multiple powered functions.

Limitations

• Higher cost.
• Greater weight in some systems.
• Requires charging and maintenance.
• Requires reliable control signals and training.

The terminal device performs the functional role of the missing hand.

Common options include:

• Prosthetic hand.
• Voluntary-opening hook.
• Voluntary-closing hook.
• Task-specific terminal devices.

Hooks can provide excellent visibility and precision for certain manual tasks despite being less cosmetic.

Osseointegration uses an implant anchored directly within the residual bone, allowing the external prosthesis to attach without a conventional load-bearing socket.

Potential Advantages

• Eliminates several socket-related problems.
• Improved prosthetic attachment.
• Improved range of motion in selected patients.
• Potentially improved sensory feedback through osseoperception.

Important Concerns

• Superficial soft-tissue infection around the skin penetration site.
• Deep infection.
• Periprosthetic fracture.
• Implant failure.
• Need for specialised rehabilitation and long-term surveillance.

• Skin abrasion.
• Pressure ulceration.
• Contact dermatitis.
• Folliculitis.
• Excessive sweating.
• Residual-limb volume fluctuation.
• Socket discomfort.
• Neuroma pain.
• Phantom limb pain.
• Contracture.
• Contralateral limb overuse.
• Back pain.
• Falls.

Phantom sensation is the perception that the amputated limb or part of it is still present.

Phantom limb pain refers to painful sensations perceived in the absent limb.

Management may include:

• Education and reassurance.
• Desensitisation.
• Pharmacological management of neuropathic pain.
• Mirror therapy.
• Graded motor imagery.
• Appropriate prosthetic use.
• Selected interventional or surgical treatment in refractory cases.

A neuroma may develop at the cut end of a peripheral nerve after amputation. It becomes clinically important when it produces localised pain, tenderness or prosthetic intolerance.

Modern surgical strategies for selected symptomatic or preventive cases include:

• Targeted muscle reinnervation.
• Regenerative peripheral nerve interface.
• Revision and relocation of nerve end in selected situations.

Targeted muscle reinnervation (TMR) transfers a divided peripheral nerve to a nearby expendable motor nerve branch.

It may help:

• Reduce symptomatic neuroma formation.
• Reduce selected forms of residual-limb and phantom pain.
• Provide improved muscle-control signals for advanced myoelectric prostheses.

Before prescribing any device, answer five questions:

1. What is the exact functional problem? Weakness, instability, pain, deformity, loss of limb or impaired gait?
2. Is the deformity flexible or fixed? A flexible deformity may be corrected; a rigid deformity may only be accommodated.
3. Which joints need control? Do not immobilise more joints than necessary.
4. What is the patient's functional potential? Consider muscle strength, cognition, balance, cardiovascular fitness and environment.
5. Will the patient actually use the device? Comfort, weight, appearance and ease of application strongly influence adherence.

Never attempt to force a rigid deformity into a “normal” position inside an orthosis.

Skin inspection is particularly important in patients with:

• Diabetes.
• Peripheral neuropathy.
• Spinal cord injury.
• Peripheral vascular disease.
• Reduced cognition.

Persistent redness, blistering, ulceration or pain after orthotic or prosthetic use should prompt review of fit and pressure distribution.

Optimal orthotic and prosthetic rehabilitation requires collaboration between:

• Orthopaedic surgeon.
• Physical medicine and rehabilitation specialist.
• Orthotist/prosthetist.
• Physiotherapist.
• Occupational therapist.
• Wound-care team.
• Pain specialist.
• Psychologist or counsellor where appropriate.
• Social and vocational rehabilitation services.

• Prescribing a brace without defining the biomechanical problem.
• Trying to correct a rigid deformity with excessive orthotic pressure.
• Immobilising more joints than necessary.
• Ignoring skin sensation and vascular status.
• Using a very rigid orthosis when dynamic assistance would be more functional.
• Failing to consider how an AFO changes knee mechanics.
• Performing an unnecessarily proximal amputation.
• Ignoring contracture prevention after amputation.
• Assuming prosthetic problems are always caused by the patient rather than socket fit or alignment.
• Choosing advanced prosthetic components without considering the patient's actual functional level.
• Neglecting rehabilitation and gait training after prosthetic fitting.

• An orthosis supports or modifies an existing body part; a prosthesis replaces a missing body part.
• Three-point pressure is one of the fundamental principles of orthotic correction.
• Increasing contact area reduces local pressure.
• Increasing the lever arm allows a given corrective moment to be produced with less force.
• AFO = ankle-foot orthosis.
• Posterior leaf-spring AFO is useful for relatively isolated foot drop.
• Ground-reaction AFO can generate an external knee-extension moment in selected patients.
• KAFO is useful when significant knee instability or quadriceps weakness accompanies ankle-foot dysfunction.
• A locked KAFO increases stability but makes gait more energy-consuming.
• HKAFO provides additional hip and pelvic control.
• Jewett brace is a hyperextension orthosis using a three-point system to resist thoracolumbar flexion.
• Scoliosis bracing primarily aims to prevent progression during growth rather than permanently correct a mature structural curve.
• Dynamic splinting may improve hand function in radial nerve palsy.
• Anti-claw splint prevents MCP hyperextension in ulnar nerve palsy.
• Preserving the knee in lower-limb amputation substantially improves prosthetic efficiency.
• Myodesis attaches muscle or tendon to bone; myoplasty joins opposing muscle groups.
• The prosthetic socket is the critical interface between the patient and the prosthesis.
• PTB stands for patellar tendon-bearing socket.
• SACH stands for solid ankle cushioned heel.
• A transfemoral prosthesis requires an artificial knee joint whereas a transtibial prosthesis preserves the patient's native knee.
• Microprocessor knees dynamically modify resistance according to gait conditions.
• Lateral trunk lean in a transfemoral amputee may be associated with hip abductor weakness or prosthetic/socket problems.
• Knee flexion contracture is particularly important after transtibial amputation.
• Hip flexion and abduction contractures are important after transfemoral amputation.
• An advanced prosthesis cannot compensate for a poorly prepared residual limb, poor socket fit or inadequate rehabilitation.

1. Define the mechanical problem first: weakness, instability, deformity, pressure overload or limb absence should guide prescription.
2. Distinguish flexible from fixed deformity: flexible deformities may be corrected; rigid deformities usually require accommodation.
3. Use basic biomechanics: three-point pressure, adequate lever arms and appropriate pressure distribution form the basis of most orthoses.
4. Control only what needs control: unnecessary immobilisation increases energy expenditure and reduces function.
5. Remember the kinetic chain: an AFO can alter knee mechanics and a foot orthosis can influence more proximal joints.
6. Preserve useful limb length: a more distal functional amputation generally produces better prosthetic efficiency when tissue viability permits.
7. Prepare the residual limb: wound healing, oedema control, strength and prevention of contracture are essential before definitive prosthetic fitting.
8. Prioritise socket fit: sophisticated prosthetic components cannot compensate for an uncomfortable or unstable socket.
9. Match technology to the patient: component choice should reflect mobility, occupation, cognition, environment and goals.
10. Rehabilitation is part of the prescription: successful orthotic and prosthetic treatment requires training, reassessment and ongoing modification.

The goal of orthotics and prosthetics is not simply to provide a device, but to restore the safest and most efficient function possible through appropriate biomechanics, fitting and rehabilitation.