Lower limb orthoses are commonly used in physical medicine for a wide range of conditions. Therefore, a sound understanding of the different types of orthoses and their biomechanical properties and indications is essential for proper prescription.
Principles of Lower Limb Orthoses (eSlide 12.1)
An orthosis is defined as a device attached or applied to the external surface of the body to improve function, restrict or enforce motion, or support a body segment. Lower limb orthoses are indicated to assist gait, reduce pain, decrease weight bearing, control movement, and minimize progression of a deformity.
Terminology for Lower Limb Orthoses
Often, the terminologies for orthoses themselves are not uniform and can be sources of confusion. The most common nomenclature uses the first letter of each joint the orthosis crosses, from proximal to distal. For example, KAFO refers to a knee-ankle-foot orthosis. Other added descriptions may include the material used [e.g., plastic ankle-foot orthosis (AFO)], function performed [e.g., reciprocating gait orthosis (RGO)], or even an eponym (e.g., Scott-Craig orthosis). An orthosis is not put on and taken off but is rather donned and doffed.
Shoes
Proper shoe fitting is important. The sole should be pliable, and the index finger should fit between the tip of the great toe and toe box. The presence of calluses from friction indicates a poor fit.
Shoe Parts (eSlide 12.2)
Two types of dress shoes are commonly worn: the Blucher and the Balmoral. A Blucher shoe has an open throat and is recommended for patients requiring an orthosis because there is more room to don and doff the shoe or orthosis. One should be familiar with the parts of the shoe, such as shank, vamp, and toe box. The heel counter is the back of the shoe, which controls the rearfoot. A strong heel counter is critical to control the entire foot.
Foot Orthoses (eSlide 12.3)
Foot orthoses range from over-the-counter arch supports to customized fabricated orthoses. They can affect ground reaction forces that act on proximal joints and rotational components during gait. Customized orthoses are usually available in soft, semi-rigid, and rigid types, depending on the needs for shock absorbency and degree of control for the specific deformity. For a custom foot orthosis, the fabrication process involves taking a cast of the foot to create a negative mold from which a positive mold is obtained. It is the positive mold that is modified and over which the final orthosis is formed. It is important that the subtalar joint be casted in a neutral position to minimize abnormal foot and ankle rotation.
Common Foot Conditions
Pes Planus (Flat Foot) (eSlide 12.3)
Pes planus can be due to abnormalities such as excessive internal torsion of the tibia (which results in pronation of the foot) or malalignment of the calcaneus. Pronation of the foot can be defined as a rotation of the foot in the longitudinal axis that results in the lowering of the medial aspect of the foot. Pronation occurs at the subtalar joint; therefore the key to controlling excess pronation is to control the calcaneus to maintain the subtalar joint in a neutral position. The orthosis should cup and elevate the anteromedial calcaneus, exerting an upward thrust against the sustentaculum tali to prevent pronation. It should also extend beyond the metatarsal heads to provide better leverage. A custom-made foot orthosis designed to prevent hyperpronation is also referred to as a UCBL orthosis (or UCB), denoting the University of California Biomechanics Laboratory.
Some cases of pes planus are because of ligamentous laxity within the foot for which medial longitudinal arch supports can be helpful. Because the foot develops a tolerance for the inlay, the height of the arch can be increased as required. A Thomas heel (provides increased medial length to the heel) can also offer medial support, particularly for heavier individuals. Runners having hyperpronation or pes planus require running shoes with a firm medial heel counter and a wide shank.
Pes Cavus (High-Arched Foot)
Pes cavus leads to excess pressure along the heel and metatarsal head areas, causing pain. Increasing the height of the longitudinal support to fill in the space between the shank of the shoe and arch of the foot, as well as extending the lift to the metatarsal heads, will evenly redistribute the weight. The high point of the arch should be located at the talonavicular joint.
If excess supination is caused by an externally rotated tibia, the foot orthosis must be molded with the subtalar joint in a neutral position to prevent excess supination.
Forefoot Pain (Metatarsalgia)
The aim is to redistribute the weight-bearing forces to an area proximal to the metatarsal heads. A metatarsal pad (cookie) can be placed inside the shoe just proximal to the second, third, and fourth metatarsal heads; proximal to the lateral aspects of the first metatarsal; and medial to the fifth metatarsal head. A metatarsal bar can be externally placed on the sole proximal to the metatarsal heads. A rocker bottom can also be used. Patients should avoid shoes with high heels or pointed toes.
Heel Pain
Again, the aim is to redistribute the weight to reduce pain. Rubber heel pads can be placed inside the shoe. A calcaneal bar is externally placed distal to the painful area to prevent the calcaneus from full weight bearing. Other modifications include shoes that have a spring for the heel set on the anterior calcaneus or a rocker bottom shoe. They place the heel strike anteriorly and the ground reaction force anterior to the painful calcaneus.
Plantar fasciitis is another common source of heel pain. For plantar fasciitis associated with hyperpronation, recommendations are similar to those for pes planus, such as an orthosis with the subtalar joint in neutral position and shoes with a firm medial heel counter and wide shank. If pes cavus is present, an elevated medial arch support or a heel well can be used. Commercially, a plantar fascia night splint, which is a prefabricated AFO that is placed in a few degrees of dorsiflexion, can provide the plantar fascia and plantar flexors with a therapeutic stretch during sleep hours.
Heel lifts help relieve some causes of Achilles pain by decreasing the amount of stretch placed on the Achilles tendon. They are only used for weeks, not months, to prevent the development of a plantar flexion contracture. They can also be helpful for treating plantar flexion spasticity or contracture.
Toe Pain
Common conditions associated with toe pain include hallux rigidus, gout, and arthritis. The aim here is to decrease pain by immobilization. A full-length carbon insert can be placed along the sole of the shoe to reduce the mobility of distal joints.
Leg Length Discrepancy
Proper limb length measurements are essential. Leg length discrepancies less than 0.5 inch do not need correction. The total discrepancy is never corrected. At most, 75% of the leg length discrepancy should be corrected. The first 0.5 inch of the discrepancy can be managed with a heel pad. Additional correction requires the heel and sole to be externally built up.
Osteoarthritis of the Knee
When medial compartment narrowing is present, lateral heel wedges of 0.25-inch thickness can be used for conservative treatment of osteoarthritis by unloading the medial compartment. Therefore these wedges may also be helpful for medial meniscus injuries.
Pediatric Shoes
Pediatric shoes should have a simple design without a heel; the soles should be soft. High-quarter or three-quarter shoes are preferred during the first few years of life. Flat feet are common in infants and children and improve over time; therefore not all flat feet need to be treated in children, especially if there are no symptoms.
Ankle-Foot Orthoses
AFOs are the most commonly prescribed lower limb orthoses. Controlling dorsiflexion and plantar flexion, mediolateral stability, and subtalar joint motion (rotation at the subtalar joint is accompanied by rotation of the tibia) should be considered. AFOs can also stabilize the knee during gait. Remember that plantar flexion creates a knee extension moment, and dorsiflexion creates a knee flexion moment.
Metal Ankle-Foot Orthoses (eSlide 12.4)
Metal AFOs are now much less common than the plastic type, although metal joints are frequently used in combination with plastic orthoses. However, older patients accustomed to metal AFOs may still want to continue with this type of AFO, and morbidly obese patients may require extra durability and stability. Ankle joint motion is controlled by pins or springs inserted into channels (anterior or posterior).
A solid stirrup is a U-shaped metal piece that is permanently attached to the shoe. Its two ends are bent upward to articulate with the medial and lateral ankle joints. The sole plate can be extended beyond the metatarsal head area for conditions requiring a longer lever arm for better control of plantar flexion.
A split stirrup has a sole plate with two flat channels for insertion of the uprights. The two uprights are now called calipers because they can open and close distally to allow donning and doffing of the AFO. A split stirrup allows removal of the uprights from the shoes so that the AFO can be worn with other shoes. The split stirrup is not as stable as the solid stirrup.
Ankle Stops and Assists
The ankle joint can be positioned in a neutral, dorsiflexed, or plantar flexed position. It is set by placement of pins and screws into the two channels of the ankle joint.
Plantar Stop (Posterior Stop)
The plantar stop is used to control plantar spasticity or help incrementally stretch plantar contractures. It is commonly set at 90 degrees. A pin is inserted into the posterior channel of the ankle joint. An AFO at 90 degrees produces a flexion moment at the knee during heel strike and may lead to an unstable gait via buckling. The opposite occurs at toe-off, with an extension moment created at the knee. A cushioned heel acts like a shock absorber at heel strike and is able to partially substitute for the dorsiflexors, which cannot be eccentrically activated when an AFO is set at 90 degrees. This helps move the ground reactive force more anteriorly at the foot and knee, stabilizing the knee. In contrast, a firm heel promotes a knee flexion moment and can be used with an AFO for a patient with genu recurvatum.
Dorsiflexion Stop (Anterior Stop)
A pin is inserted into the anterior channel of the ankle joint. It is used in conditions with weak calf muscles (gastrocnemius or soleus complex) or quadriceps and is usually set at 5 degrees of dorsiflexion. The anterior stop assists with push-off and assists the knee joint into extension. It should be used in combination with a stirrup and the sole extended to the metatarsal heads. The earlier the dorsiflexion stop occurs during the stance phase, the greater the extension moment at the knee, which substitutes weak quadriceps. A balance should be obtained such that the extension at the knee is sufficient for stability yet prevents genu recurvatum.
Dorsiflexion Assist (Posterior Spring)
A posterior spring substitutes for concentric contraction of dorsiflexors to prevent flaccid foot drop after toe-off, and it also substitutes (albeit inadequately) for the eccentric activation of the dorsiflexors after heel strike. The posterior spring prevents rapid plantar flexion at heel strike during its compression in the posterior channel. The spring is again compressed during plantar flexion in the late stance before toe-off. It provides a downward thrust posterior to the ankle joint at toe-off, which results in dorsiflexion anterior to the ankle joint, helping in toe clearance during the swing phase.
Metal Ankle-Foot Orthosis Varus-Valgus Control (eSlide 12.4)
Varus and valgus deformities are associated with rotation at the subtalar joint. A T strap is attached along the side of the shoe distal to the subtalar joint to help minimize the deformity. T straps may be placed medially or laterally. A lateral T strap is used to control a varus deformity and vice versa.
Plastic Ankle-Foot Orthoses (eSlide 12.5)
Plastic AFOs are now the most commonly used AFOs because of their cost, cosmesis, light weight, interchangeability with shoes, ability to control varus or valgus deformities, and provision of better foot support.
Plastic Ankle-Foot Orthosis Components
The footplate can be extended beyond the toes to reduce spasticity aggravated by toe flexion.
The strength of the AFO should be matched to the patient’s weight and activity level. The ankle and subtalar joints can be made more stable by the following: (1) extending the trim line (anterior border of the plastic AFO) more anteriorly at the ankle level, (2) making the plastic material thicker, (3) placing carbon inserts along the medial and lateral aspects of the ankle joint, or (4) incorporating corrugations within the posterior leaf of the AFO.
Plastic AFOs can also be hinged at the ankle, permitting a more natural gait. Plastic ankle joints are light and are a good choice for children. Metal ankle joints are preferred for adults, particularly heavy adults. Newer designs have a single midline posterior pin/spring mechanism. Hinging an AFO adds mediolateral stability. The leg component should encompass three-quarters of the leg and should be padded along its internal surface. The proximal extent should end 1 inch below the fibular neck to prevent compressive common peroneal nerve palsy.
Solid Plastic Ankle-Foot Orthoses
The term solid refers to an AFO that is made of a single piece of plastic. It does not have ankle joints. However, the trim line of the AFO will determine the level of flexibility and control at the ankle. Anterior trim lines (anterior to the medial malleolus) are the most rigid (but still flexible enough to allow some ankle motion), whereas posterior trim lines (behind the medial malleolus) provide some flexibility (with little or no mediolateral control).
Solid AFOs set at 90 degrees are commonly used for foot drop. The AFO can be fixed in a few degrees of plantar flexion to provide stability at the knee during the stance phase of gait. Genu recurvatum can also be treated with a solid AFO. The more rigid the AFO, the greater the flexion moment at the knee at heel strike. The flexion moment at the knee becomes even greater during midstance if the ankle is placed in a few degrees of dorsiflexion.
Plastic Ankle-Foot Orthoses Varus-Valgus Control (eSlide 12.6)
A three-point system is used to provide the counterforces necessary to oppose the forces of the deformity. An equinovarus (or inversion) deformity is controlled by applying forces medially at the metatarsal head area and calcaneus. The third force is applied more proximally along the lateral aspect of the distal fibula. A more proximal medial tibial force is applied to stabilize the leg portion of the plastic AFO by providing an opposing force to the fibular area. It is reversed for valgus control.
Patellar Tendon–Bearing Ankle-Foot Orthoses (eSlide 12.7)
A patellar tendon–bearing (PTB) AFO uses the patellar tendon and tibial condyles to partially relieve weight-bearing stress on skeletal structures distally, with more weight bearing distributed along the medial tibial condyle. PTB is actually a misnomer because only approximately 10% of the weight is distributed along the patellar tendon and medial tibial condyle. Most of the weight bearing is distributed throughout the soft tissues of the leg that are compressed by an appropriately fitted orthosis. PTB AFOs are often prescribed for diabetic ulcerations of the foot, tibial fractures, painful heel conditions (such as calcaneal fractures), ankle fusions in the postoperative period, Charcot joint, and avascular necrosis of the foot or ankle.
Charcot Restraint Orthotic Walker Boot (eSlide 12.7)
The Charcot restraint orthotic walker (CROW) boot is a custom-molded bivalve plastic AFO that accommodates the entire foot and leg up to the knee for the purpose of off-loading a plantar ulcer or stabilizing the progressive deformity from the Charcot joint of the foot and ankle. The device has a rocker bottom and rubber sole for indoor and outdoor ambulation.
Pressure Relief Ankle-Foot Orthoses
A pressure relief AFO (PRAFO) serves the following two purposes: pressure relief (avoiding pressures at the heel and malleoli) and contracture prevention at the immobilized or motionless lower limb.
Common Ankle-Foot Orthosis Prescriptions ( see eSlide 12.5 )
The most common AFO prescription for foot drop is a posterior leaf spring AFO, but for associated significant subtalar joint instability, a hinged plastic AFO with metal double-action ankle joints with springs in the posterior channels or a hinged, spring-loaded midline posterior stop AFO may be a better option.
For plantar spasticity, common prescriptions include either a hinged custom plastic AFO with a single midline posterior stop or a hinged custom plastic AFO with pins in the posterior channels to provide a plantar stop at 90 degrees. Permitting dorsiflexion allows a more normalized gait and provides a therapeutic stretch to the plantar flexors. Prefabricated carbon fiber AFOs are also available. The advantages of carbon fiber AFOs are lighter weight, lower profile footplate, and ability to provide some dynamic response or propulsion to substitute for weak plantar flexors.
For lumbar spinal cord injury, the typical AFO prescription is a bilateral custom plastic ground reaction (anterior tibial shell closing) AFO that is fixed in 10 degrees of plantar flexion. The plantar flexion creates knee extension moments with weight bearing to add stability to the knees during ambulation.
Checkout
The patient should be examined after fitting and using the orthosis to verify gait improvement and ease of donning and doffing. When the orthosis is off, the skin should be carefully observed for areas of breakdown.
Knee-Ankle-Foot Orthoses
The components of KAFOs include knee joints, knee locks, thigh uprights, and proximal thigh bands. KAFOs are used in patients with severe knee extensor and hamstring weakness, structural knee instability, or knee flexion spasticity.
Knee Joints (eSlides 12.8 and 12.9)
There are three basic types of knee joints. The straight set knee joint provides rotation about a single axis. It allows free flexion but prevents hyperextension. It is often used in combination with a drop lock. The polycentric knee joint uses a double-axis system to simulate the flexion-extension movements of the femur and tibia at the knee joint. It also adds bulk to the orthosis. It is most frequently used in sport knee orthoses. The third type of knee joint is the posterior offset knee joint. It is prescribed for patients with weak knee extensors and some hip extensor strength. It helps keep the orthotic ground reactive force in front of the knee axis during stance. If additional knee stability is needed, the ankle component of the KAFO can also be set at 10–15 degrees of plantar flexion.
Knee Locks (eSlide 12.10)
There are four common types of knee locks. The ratchet lock has recently become the most commonly prescribed knee lock. It has a catching mechanism that operates in 12-degree increments. It has an element of safety because it keeps the gains made toward extension as the user rises from a seated to standing position. Knee flexion is achieved either by pressing down on a release lever or by sliding the locking mechanism. The drop lock (ring lock) is commonly used in both the medial and lateral uprights of the KAFO. Its advantage is simplicity of design without bulk. However, fine motor coordination skills are needed to lock and unlock the knee in complete extension. The bail lock (also known as the Swiss, French, Schweitzer, or pawl lock) provides the easiest method of simultaneously unlocking the medial and lateral knee joints of a KAFO. Two hands can be used for two bail locks. The locking mechanism is spring loaded to assist locking the knee in extension.
The dial lock (formerly known as a turn buckle) is used to stabilize the knee in varying amounts of flexion. It can be adjusted in 6-degree increments and is more precise for management of a knee with a flexion contracture than a KAFO with ratchet locks. Its uses include preventing progression of a flexion contracture or assisting with gradual reduction of a flexion contracture.
Thigh and Calf Components of a Knee-Ankle-Foot Orthosis
The thigh and calf bands can consist of either padded metal bands or molded plastics, but they need to be wide enough to adequately distribute the pressure for comfort.
Scott-Craig Orthosis
The Scott-Craig orthosis was designed for patients with paraplegia who have a complete lesion at L1 or higher. The orthotic design consists of an offset knee joint with a bail lock and an ankle with a dorsiflexion stop and a posterior stop set at 90 degrees.
Stance Control Orthosis
The stance control KAFO is designed to lock the knee in the stance phase and allow knee flexion in the swing phase of gait. This category of KAFOs is still evolving, but currently, there are several orthotic manufacturers that offer stance control knee joints in centrally fabricated KAFOs.
Knee Orthoses (eSlide 12.11)
Swedish Knee Cage
The knee orthosis (KO) known as a Swedish knee cage is used to control minor to moderate genu recurvatum. The Swedish knee cage uses a classic three-point orthotic system. Severe genu recurvatum might need to be controlled with longer lever arms, such as those offered by a KAFO.
Osteoarthritis Knee Orthoses
Osteoarthritis KOs are commonly used in patients with medial compartment narrowing. The three-point system distribution is achieved by a strap that is applied across the knee joint. The foot orthosis with a lateral buildup is considered to be the preferred first-line orthotic treatment for osteoarthritis of the knee.
Sport Knee Orthoses
Sport KOs can be divided into prophylactic, rehabilitative, and functional categories. Prophylactic knee bracing attempts to prevent or reduce the severity of knee injuries. Rehabilitative knee bracing is used to allow protected motion within defined limits. It is useful for postoperative and conservative management of knee injuries, such as anterior cruciate ligament–reconstructed knees and patellofemoral pain syndrome. Functional knee bracing is designed to assist or provide stability for the unstable knee and most commonly to stabilize a laterally subluxing patella or an anterior cruciate ligament–deficient knee.
Pediatric Orthoses (eSlide 12.12)
Caster Cart
The caster cart is used for children with a developmental delay in ambulatory skills. It serves as an initial mobility aid and is most often prescribed for children with spina bifida.
Standing Frame
The age range for initial use of the standing frame is usually 8–15 months. Children who pull themselves up along furniture are typically ready for a standing frame. The standing frame helps balance the body in space and allows free use of the upper limbs for participation in activities.
Parapodium/Swivel Orthosis
A parapodium is an appropriate prescription for children who are unlikely to become functional walkers because of the severity of their impairment. It often complements wheelchair use. It is most commonly prescribed for children between 2.5 and 5 years of age. Ambulation occurs by the child pivoting the hips to swivel one side of the oval-based stand forward and then repeating the same action for the other side. A parapodium is similar to the standing frame, but it has hip and knee joints that can be unlocked to permit sitting.
Reciprocating Gait Orthosis
The purpose of the RGO is to provide contralateral hip extension with ipsilateral hip flexion. The RGO is appropriate for children who have used the standing frame, developed good trunk control and coordination, can safely stand, and are mentally prepared for ambulation. Good upper limb strength, trunk balance, and active hip flexion are important positive variables for ambulation. Spinal cord injury level is not a very reliable predictor of ambulation capability in children. The RGO is prescribed most commonly for children aged 3–6 years.
Ambulation Aids (eSlide 12.13)
The purpose of using ambulation aids is to increase the area of support. Their proper use requires adequate upper limb strength and coordination. The type of aid needed depends on how much balance and weight-bearing assistance are required. The body weight transmission for a unilateral cane opposite the affected side is 20%–25%. It is 40%–50% with the use of a forearm or arm cane. Body weight transmission with bilateral crutches is estimated to be up to 80%.
Aids include canes such as C canes and quad canes. Canes are used on the side opposite the supporting lower limb. A walker provides maximum support for the patient but also necessitates a slow gait. A crutch is defined as a device that provides support from the axilla to the floor. Nonaxillary crutches include the Lofstrand forearm orthosis, Kenny stick, Everett or Warm Springs crutch, Canadian crutch, platform forearm orthosis.
Prescription (Box 12.1)
A medical diagnosis with delineation of the impairment and any resulting disability should be made before an orthotic prescription is written. The orthotic goals should be documented for the orthotist.
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