General Description - Lower Limb Orthotics PDF Print E-mail

1. Introduction:

A lower limb orthosis, like the one in the image below, is an external device applied or attached to a lower body segment to improve function by controlling motion, providing support through stabilizing gait, reducing pain through transferring load to another area, correcting flexible deformities, and preventing progression of fixed deformities.

 

 

Thermoplastic molded ankle-foot orthosis (posteri...

Thermoplastic molded ankle-foot orthosis (posterior leaf spring, minimal resistance, moderate resistance, maximal resistance/solid ankle-foot orthosis).

2. Terminology

Orthosis (or orthotic device) is the medical term for what most people would refer to as a brace or splint. Orthoses generally are named by the body regions that they involve, as demonstrated by the following abbreviations:

 

  • AFO is an ankle-foot orthosis.

  • KAFO is a knee-ankle-foot orthosis. (See image below.)
  • Plastic shell and metal uprights molded knee-ankl...
  • HKAFO is a hip-knee-ankle-foot orthosis.
  • THKAFO is a trunk-hip-knee-ankle-foot orthosis.

3. Locomotion and gait

The total mass of the body can be considered concentrated at one point, called the center of gravity. The center of mass is located in the midline, just anterior to the second sacral vertebra while the individual is standing and walking. The center of mass changes with the configuration and function of the body.

The line of gravity is a line passing through the center of gravity to the center of the earth. This line (1) arises from the supporting surface between the ball and heel of the foot, then (2) passes in front of the ankle and knee joints and slightly behind the hip joint to the center of gravity, then (3) passes through the lumbosacral junction and behind the lumbar vertebral bodies to intersect the spine at the thoracolumbar junction, then (4) continues in front of the thoracic vertebral bodies and through the cervicothoracic junction, and, lastly, (5) travels behind the cervical vertebral bodies to the occipitocervical junction. When the center of gravity does not fall through the area of support, it is unstable at that moment.

Gait cycle is defined as the activity that occurs between the initial contact of one extremity and the subsequent initial contact of the same extremity. During a single gait cycle, each extremity passes through 1 stance phase and 1 swing phase. Stance phase occupies over 60% of the gait cycle during walking at average velocity. Stance phase includes initial contact, loading response, midstance, terminal stance, and preswing. Swing phase includes initial swing, mid swing, and terminal swing.

The average total displacement of the center of gravity in the vertical and lateral directions is less than 2 inches in normal gait. The increase in displacement of the center of gravity increases the amount of energy for walking.

The purpose of using an orthosis is to enhance normal movement and to decrease abnormal posture and tone. Lower extremity orthoses can be used to correct abnormal gait patterns and to increase the efficiency of walking.

4. Lower extremity orthotics

An orthosis is classified as a static or dynamic device. A static orthosis is rigid and is used to support the weakened or paralyzed body parts in a particular position. A dynamic orthosis is used to facilitate body motion to allow optimal function. In all orthotic devices, 3 points of pressure are needed for proper control of a joint.

4.1. Principles

A lower limb orthosis should be used only for specific management of a selected disorder. The orthotic joints should be aligned at the approximate anatomic joints. Most orthoses use a 3-point system to ensure proper positioning of the lower limb inside the orthosis.

The orthosis selected should be simple, lightweight, strong, durable, and cosmetically acceptable. Considerations for orthotic prescription should include the 3-point pressure control system, static or dynamic stabilization, flexible material, and tissue tolerance to compression and shear force.

4.2. Materials

An orthosis, like the one shown below, can be constructed from metal, plastic, leather, synthetic fabrics, or any combination. Plastic materials, such as thermosetting materials and thermoplastics, are the materials most commonly used in the orthotic industry.

Thermoplastic molded ankle-foot orthosis (posteri...

  • Plastics
    • Thermosetting materials can be molded into permanent shape after heating. They do not return to their original consistency even after being reheated. Thermoplastic materials soften when heated and harden when cooled.
    • Low-temperature thermoplastics can be fabricated easily and rapidly with hot water or hot air and scissors, but they are used mainly in low stress activities.
    • High-temperature (polypropylene) thermoplastics require higher temperature (150°C) to mold, but they are ideal for high stress activities.
  • Leather, such as cattle hide, is used for shoe construction because it conducts heat and absorbs water well.
  • Rubber
    • Rubber has tough resiliency and shock-absorbing qualities.
    • Rubber is used for padding in body jackets and limb orthoses.
  • Metal
    • Metals, such as stainless steel and aluminum alloys, are adjustable, but they are heavy and not cosmetically pleasing.
    • Metals can be used for joint components, metal uprights, sprints, and bearings. (See images below.)
    • Double upright metal ankle-foot orthosis. Double upright metal ankle-foot orthosis.
    • Double upright metal knee-ankle-foot orthosis. Double upright metal knee-ankle-foot orthosis.
    • Plastic shell and metal uprights molded knee-ankl... Plastic shell and metal uprights molded knee-ankle-foot orthosis with drop lock joints.

 

Article Reference: http://emedicine.medscape.com/article/314838-overview

 

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