LOWER LIMB ORTHOTICS

LOWER LIMB ORTHOTICS

A lower limb orthosis 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.

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:

v  AFO   : - Ankle-Foot Orthosis.

v  KAFO   : - Knee-Ankle-Foot Orthosis.

v  HKAFO   : - Hip-Knee-Ankle-Foot Orthosis.

v  THKAFO   : - Trunk-Hip-Knee-Ankle-Foot Orthosis.

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 [S-2] 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.

o   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.

o   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.

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.

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.

MATERIALS

An orthosis 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.  

SHOES AND FOOT ORTHOTICS

SHOES

Shoes are the important foundation of the lower limb orthosis. Shoes are used to protect and warm the feet, transfer body weight while walking, and reduce pressure or pain through redistributing weight.

Shoes should be comfortable and properly fitted. They should be at least 1 cm longer than the longest toe and correspond to the shape of the feet.

The shoe can be divided into lower and upper parts.

The lower parts consist of the sole, shank, ball, toe spring, and heel.

The upper parts include the quarter, heel counter, vamp, toe box, tongue, and throat.

PARTS OF THE SHOE

SHOE MODIFICATIONS

A properly fitted shoe should have adequate room for the foot to expand while the patient is bearing weight.

The shoe should be at least 1 cm longer than the longest toe, and the widest part also should correspond to the widest part of the foot.

Shoes can be modified to reduce pressure on sensitive areas by redistributing weight toward pain-free areas.

EXTERNAL SHOE MODIFICATIONS

INTERNAL SHOE MODIFICATIONS

FOOT ORTHOSIS

The foot orthosis extends from the posterior border of the foot to a point just posterior to the metatarsal heads.

This device is used to accommodate the abnormal foot to help restore more normalized lower limb biomechanics.

Orthotic inserts include the following:

In a randomized clinical trial, a Canadian study investigated the effectiveness of custom-made orthoses versus that of prefabricated ones, with both types tested over a 4-week period in patients with lower extremity musculoskeletal pain.

The report’s authors determined that although both types of orthoses brought immediate improvement in economy of gait, only the custom-made orthoses enabled patients to maintain such improvement over the entire 4-week period.

ANKLE-FOOT ORTHOTICS

An ankle-foot orthosis (AFO) is commonly prescribed for weakness or paralysis of ankle dorsiflexion, plantar flexion, inversion, and eversion.

AFOs are used to prevent or correct deformities and reduce weight bearing.

The position of the ankle indirectly affects the stability of the knee with ankle plantar flexion providing a knee extension force and ankle dorsiflexion providing a knee flexion force.

An AFO has been shown to reduce the energy cost of ambulation in a wide variety of conditions, such as spastic diplegia due to cerebral palsy, lower motor neuron weakness of poliomyelitis, and spastic hemiplegia in cerebral infarction.

Thermoplastic AFOs - These devices are plastic molded AFOs, consisting of the following 3 parts:

(1) A shoe insert,

(2) A calf shell, and

(3) A calf strap attached proximally

The rigidity depends on the thickness and composition of the plastic, as well as the trim line and shape.

Thermoplastic AFOs are contraindicated in cases of fluctuating edema and insensation.  

METAL AND METAL-PLASTIC AFOS

This type of AFO consists of a shoe or foot attachment, ankle joint, 2 metal uprights (medial and lateral), with a calf band (application of force) connected proximally.

The stirrup anchors the uprights to the shoes between the sole and the heel. The caliper is a round tube placed in the heel of the shoe, which connects to the uprights and also allows for easy detachability of the uprights.

A molded shoe insert is another alternative to fit the stirrup into the shoe, which also allows maximum control of the foot and aligns the anatomic and mechanical ankles.

Ankle joints - The mechanical ankle joints can control or assist ankle dorsiflexion or plantar flexion by means of stops (pins) or assists (springs). The mechanical ankle joint also controls mediolateral stability. Knee extension moment is promoted by ankle plantar flexion, and knee flexion moment is promoted by ankle dorsiflexion.

v  Free motion ankle joint - The stirrup has a completely circular top, which allows free ankle motion and provides only mediolateral stability.

v  Plantar flexion ankle joint stop - This ankle joint stop is produced by a pin inserted in the posterior channel of the ankle joint or by flattening the posterior lip of the stirrup's circular stop. The plantar flexion stop has a posterior angulation at the top of the stirrup that restricts plantar flexion but allows unlimited dorsiflexion and promotes knee flexion moment. This design is used in patients with weakness of dorsiflexion during swing phase and flexible pes equinus.

v  Dorsiflexion ankle joint stop - The stirrup has a pin inserted in the anterior channel of the ankle joint or by flattening the anterior lip of the stirrup's circular stop. The dorsiflexion stop has an anterior angulation at the top of the stirrup that restricts dorsiflexion but allows unlimited plantar flexion and promotes a knee extension moment in the meantime. This design is used in patients with weakness of plantar flexion during late stance.

v  Limited motion ankle joint stop - This ankle joint stop has anterior and posterior angulations at the top of the stirrup with restricted dorsiflexion and plantar flexion ankle motion. The limited motion ankle joint stop has a pin in the anterior and the posterior channel, and it is used in ankle weakness affecting all muscle groups.

v  Dorsiflexion assist spring joint - This joint has a coil spring in the posterior channel and helps to aid dorsiflexion during swing phase.

v  Varus or valgus correction straps (T-straps) - A T-strap attached medially and circling the ankle until buckling on the outside of the lateral upright is used for valgus correction. A T-strap attached laterally and buckling around the medial upright is used for varus correction.

KNEE-ANKLE-FOOT ORTHOTICS AND KNEE ORTHOTICS

Knee-ankle-foot orthotics (KAFOs) consists of an AFO with metal uprights, a mechanical knee joint, and 2 thigh bands.

KAFO can be used in quadriceps paralysis or weakness to maintain knee stability and control flexible genu valgum or varum.

 

KAFO also is used to limit the weight bearing of the thigh, leg, and foot with quadrilateral or ischial containment brim.

A KAFO is more difficult to don and doff than an AFO, so it is not recommended for patients who have moderate-to-severe cognitive dysfunction.

KNEE ORTHOSES

A knee orthosis (KO) only provides support or control of the knee but not of the foot and ankle. The knee joint is centered over the medial femoral condyle.

If the patient does not have adequate gastrocnemius delineation so that there is a shelf for the distal end of the orthosis to rest on, the brace may slide down the leg with wear. In that case, the brace needs to extend to the sole of the foot.

HIP-KNEE-ANKLE-FOOT ORTHOTICS

A hip-knee-ankle-foot orthosis (HKAFO) consists of a hip joint and pelvic band in addition to a KAFO.

The orthotic hip joint is positioned with the patient sitting upright at 90°, while the orthotic knee joint is centered over the medial femoral condyle.

Pelvic bands complicate dressing after toileting unless the orthosis is worn under all clothing. Pelvic bands increase the energy demands for ambulation.

TRUNK-HIP-KNEE-ANKLE-FOOT ORTHOTICS

A trunk-hip-knee-ankle-foot orthosis (THKAFO) consists of a spinal orthosis in addition to a HKAFO for control of trunk motion and spinal alignment.

A THKAFO is indicated in patients with paraplegia and is very difficult to don and doff.

v  Reciprocating gait orthosis (RGO) - An RGO consists of bilateral KAFOs with posteriorly offset locking knee joints, hip joints, and a custom-molded pelvic girdle with a thoracic extension. The hip joints are coupled with cables preventing bilateral hip flexion simultaneously. The hip extension on one side coupling hip flexion on the other side through the cables produces reciprocal walking gait pattern. The RGO combined with functional electronic stimulation (FES) can be used for 2-point or 4-point gait patterns in ambulatory paraplegic or tetraplegic (C8) patients. Using the RGO with FES can double the patient's optimum gait speed, lower blood pressure and heart rate, and increase oxygen uptake as compared with ambulating with the RGO without FES.

v  Para walker - This device is a hip guidance orthosis, which consists of bilateral KAFOs with a ball-bearing hip joint and a body brace. Ambulation is performed through trunk motion transmitted to the lower extremities with hip flexion and extension via the brace. Hip flexion is restricted by a stop, and hip extension may be free or limited by a stop. The para walker is developed for patients with SCI. A study of 5 paraplegic patients found an average reduction in oxygen consumption of 27%, with 33% faster ambulatory rate compared with the RGO.

v  Parapodium - This device is developed for pediatric myelodysplastic patients to allow them to stand without crutches for functional activities with their upper limbs free. The parapodium consists of a shoe clamp, aluminum uprights, a foam knee block, and back and chest panels. Hip and knee may be locked for standing and unlocked for sitting. A torque converter under the base allows side-to-side rocking to be translated into forward propulsion.

v  Standing frame - This allows standing but does not permit hip and knee flexion. The standing frame is used for children to learn standing balance and achieve a swing-through gait.

SPECIAL PURPOSE LOWER LIMB ORTHOTICS