Floor (Ground) Reaction AFO
Floor Reaction Orthosis (FRO), Floor reaction AFO (FRAFO), Ground reaction AFO (GRAFO)
· Wu 1990 defines an ankle foot orthosis (AFO) as “a medical mechanical device to support and align the ankle and foot, to suppress spastic and overpowering ankle and foot muscles, to assist weak and paralysed muscles of the ankle and foot, to prevent or correct ankle and foot deformities, and to improve the functions of the ankle and foot.”
· Early in the 1980s, the floor-reaction principles at work in Saltiel‘s patellar tendon-bearing, knee-locking ankle-foot orthosis for paralytic disability were applied to the problem of crouch deformity in children with cerebral palsy. The anterior floor-reaction orthosis (AFRO) was created as a result. The solid crouch-control ankle-foot splint (AFS) was developed concurrently with the AFRO, although without the benefit of influence.
TYPES OF ORTHOSES
An Orthosis is named according to the joints of the leg that are covered by the orthosis.
o AFO – Ankle- Foot Orthosis – Covers the foot and ankle and extends partway up the calf.
o KAFO – Knee-Ankle-Foot Orthosis – Covers the foot, ankle and knee and extends part way up the thigh.
o HKAFO – Hip –Knee-Ankle-Foot Orthosis – Covers the foot, ankle, knee and hip and includes the pelvis.
o SMO – SupraMalleolar Orthosis – Similar to the AFO but come just above the ankle bone (the malleolus).
o Shoe insert – fits inside the shoe and controls the position of the foot.
Orthoses are also named by some of the following features:
o Solid/Fixed – Designed to hold the joint in a fixed position (i.e., A solid ankle AFO does not allow motion at the ankle joint.)
o Hinged/Articulated – the orthosis has a hinge that allows a limited amount of motion. (i.e., A hinged AFO allows limited up and down motion of the ankle)
o Dynamic – the material the orthosis is made of has some flexibility that allows limited motion at the joint.
o Contoured – usually refers to special shaping of the foot plate that encourages desired movement of the foot.
o Floor reaction – specially designed to limit a crouched gait (walking with knees bent in the crouched position)
§ An AFO is a device that supports the ankle and foot area of the body and extends from below the knee down to and including the foot. This device is used to control instabilities in the lower limb by maintaining proper alignment and controlling motion.
§ Most common orthosis –
2. Total Contact
3. Floor reaction
§ Most AFO’s can be articulating or non-articulating
§ A floor (ground) reaction AFO (FRAFO or GRAFO) is a custom fabricated, molded plastic device.
§ Stiff enough to provide ground reaction forces for quadriceps weakness
§ Uses floor reaction force through toe aspect of foot plate to prevent forward tibial progression & subsequent knee collapse.
Principles: mechanical and biomechanical
§ Based on Newton’s third law, which states that for every action, there is an equal and opposite reaction. This means that during stance the sum of the body weight and the acceleration of the centre of mass (CM) acting downwards creates an equal and opposite reaction force acting upwards. This is known as the ground reaction force (GRF). The GRF has a point of application on the sole of the foot, a magnitude, a line of action and a direction, which all vary in a fairly repetitive fashion during gait. This reaction force can be decomposed into three components: vertical, lateral shear and progressional shear GRF. The latter two are small compared to vertical GRF and result from any non-perpendicular components of the GRF.
Figure: External moment caused by ground reaction force
Figure: Moment equals force times distance
§ If the GRF passes at a distance from the centre of a joint, it creates a turning effect known as an external moment (Figure). The size of this moment (m) depends on the magnitude of the force (f), and its perpendicular distance from the joint (d), ie m=f x d. If the external moment (in this case a knee flexion moment) is to be resisted, an opposing internal extension moment must be created (by the quadriceps). If the GRF is far from the joint (ie ‘d’ in the equation is large), the external moment it creates will be large, and as a consequence, so will the internal moment required to resist motion. If an adequate internal moment cannot be created, an orthosis may be required to provide joint control and improve gait.
§ Orthoses control joints by applying systems of forces that create moments. As the size of any moment is the product of force and distance, the forces applied can be reduced if they are applied as far away from the joint as possible (Figure). In practice, the lever arm is limited by the length of the anatomical segments involved or by other considerations such as tissue intolerance to pressure.
§ It is also important that the orthosis should apply force (f) over as large an area (a) as possible in order to reduce tissue pressure (p), which is equal to force divided by area (p = f/a).
§ Solid FRAFO is fabricated to provide ankle stabilization, limits plantar & dorsiflexion and controls subtalar motion. Anterior shell assists weak quadriceps and subsequent knee flexion.
§ The design of a FRAFO included a full toe plate, rigid ankle, and an anterior tibial shell section. The combination of these three components allow the plantarflexion-knee extension couple (PF/KE) to occur, causing a knee-extension moment. This knee-extension couple helps to support weak quadriceps and plantarflexor muscles.
§ Pressure against the innervated area of skin just anterior and distal to the knee joint will provide proprioceptive feedback.
§ FRAFOs in children with spastic diplegic CP who exhibit a moderate or severe knee flexion (crouch gait) with excessive ankle dorsiflexion motion during the stance phase. FRAFO use showed significant kinematic gait improvements including a reduction of abnormal ankle dorsiflexion and knee flexion motion.
§ Stiff AFOs prevent plantarflexion of the foot in swing phase and improve ground clearance, reducing the risk of tripping by applying a system of three forces to the posterior calf, the plantar surface of the foot near the metatarsal heads, and the dorsum of the foot near the ankle joint. Where there is increased tone an ankle strap should be considered. This should be positioned so that it applies the force at approximately a 45º angle.
§ Supination of the foot affects the subtalar joint and the midtarsal joint, and the AFO must control both simultaneously. At the subtalar joint, hindfoot inversion is controlled by forces applied to the medial aspect of the heel (calcaneus), the area above the lateral malleolus, and at the medial aspect of the proximal calf. At the midtarsal joint, internal rotation of the forefoot (adduction) is controlled by the application of forces to the medial heel (calcaneus), the lateral midfoot (midtarsal joint) and along the first metatarsal shaft. Full correction of supination is important as if it is not addressed this foot position may contribute to the generation of increased varus moments at the knee, which can lead to ligamentous laxity (lateral collateral ligament) and increasing varus deformity over time.
Designs of FRAFO’s:
Weight: light weight 300 gms
Set in 3-5 degrees of plantarflexion
1. One piece: encloses the back of the lower calf, the shin, and bottom of the foot (figure)
2. Two piece: same as the one piece but has a removable anterior (front) panel
3. Rear-opening: encloses the front of the leg and top of the foot. May be articulated.
patients affected by neurological conditions:
§ spina bifida
§ cerebral palsy
§ brain injury
§ spinal cord injury
§ post-polio paralysis
§ To maintain the affected joints in proper alignment
§ To accentuate knee extension at midstance
§ Compensate for weak or absent gastroc-soleus (calf) muscles.
§ A FRAFO places the extension force closer to the knee than other AFO’s and uses a rigid anterior shell with padding. Figure: Force system to prevent equinus
§ Limiting the ankle dorsiflexion in the single support and consequently improving knee extension.
§ Provides a means of controlling or eliminating ankle and subtalar motion. By controlling the more distal joint, one can theoretically alter the ground reaction force and effect more proximal joints by the principal of the coupling.
§ FRAFO limits the second rocker, improves knee extension, and consequently increases knee external extension moment.
§ Effective to improve the extension of the knees and ankle in the stance of children with spastic cerebral palsy.
§ A GRAFO should be considered when knee flexion control cannot be achieved with a solid AFO.
§ the benefits of a FRAFO in patients with myelomeningocele included improved knee and ankle function in the sagittal plane. An increased knee extension in terminal stance and an increased knee range of motion in patients with L-4 and L-5 myelomeningoceles were also reported.
§ The FRAFO is commonly prescribed in the attempt to decrease knee flexion during the stance phase in the cerebral palsy (CP) gait.
· The first day begin by wearing for only 1 hour.
· On day two, put the FRAFO on for 2 hours.
· If skin is okay, gradually increase wearing time by 1 hour each day, checking skin after each wearing time.
· FRAFO will not improve kinematics if knee or hip flexion is a fixed deformity. Whenever possible fixed deformities should be corrected prior to bracing for the principle of coupling to be effective.
· presence of dynamic contracture of the knee and/or hip will compromise the effectiveness of a GRAFO.
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