Foot and ankle splints

Chris Drake, SRorth, Dip OTC, M.B.A.P.O. is a State Registered Orthotist. Here he discusses foot and ankle splints, otherwise known as orthoses. What are they? What do they do? And what's the difference between them?

What is an orthosis?

"An Orthosis is an externally applied device used to modify the structural or functional characteristics of neuro-musculo-skeletal system"
As defined by The International Organisation for Standardisation (ISO)

What is it used for?

Ankle and foot splints, or orthoses, have been used for many years in the management of walking patterns in children with hemiplegia. They are used in preventing unwanted and uncontrolled movements associated with muscle imbalances and increased tone in the lower leg and the foot and ankle.

Abnormal movement in children with hemiplegia

Abnormal movement with reference to the child with hemiplegia usually means a tip toe walking pattern (Equinus or a Plantarflexed Gait), with the added complication of the ankle become twisted outwards (Varus ankle) or inwards (Valgus ankle).

The adoption of a toe-walking gait also leads to secondary problems related to control of the knee which in many cases tends to snap backwards further than it would normally (Hyperextension), this in turn has a subsequent effect on hip position and a general reduction in the child’s balance. I am sure many parents will be familiar with this type of walking.

Ankle/foot orthosis (AFO)

A child with a toe walking gait pattern as you would expect is undesirable as it has a detrimental impact on the child’s posture as well as the potential problems of fixed deformities of the ankle and knee occurring later in life. One way of assisting in the prevention of this type of walking is with the fitting of a below-knee ankle/foot orthosis (AFO) which can control the movement of the foot and ankle and position it in a more normal alignment. A well made good fitting AFO will control the unwanted movements in the foot and ankle and can also influence hip and knee position. This in turn can lead to a dramatic improvement in the child’s gait, balance and posture.

How AFOs work

At first AFOs were manufactured of traditional metal and leather and then fitted to a supportive boot or other type of footwear. These tended to be heavy, unsightly and ineffective in maintaining the correct alignment over a period of time. The advent of modern thermoplastics meant that lightweight full contact AFOs could be manufactured from a cast taken of the child’s lower leg. This allowed them to be fitted into the child’s own footwear which meant greater acceptance. This close fit of the thermoplastic AFO meant improved control and greater effectiveness.

At first they were made with a solid ankle complex which held the foot and ankle at 90° to the lower leg (Neutral plantargrade position). This prevented the foot and ankle from being pushed down (Plantarflexion) and subsequently a toe walking gait. Unfortunately this also meant that the movement of the foot and ankle upwards (Dorsiflexion) was also lost. Dorsiflexion is vital for many of the daily activities and for a smooth progressive gait pattern.

Dorsiflection

Concentrate for a moment on your foot and ankle position when you are walking up hill, climbing or descending stairs, getting up from a chair or bending down to pick up your car keys. You will notice the importance of dorsiflexion in all these activities. Dorsiflexion allows for many functions to be achieved easily without overstressing other joints. It also occurs in walking to help make it energy cost efficient. Without dorsiflexion gait tends to be jerky and stick-like as it is difficult for the body and leg to pass over the effected foot and ankle during walking.

Hinged AFOs

While the fitting of an fixed AFO is very effective at preventing a toe walking gait and also the sideways movements of the ankle (Valgus & Varus movents) it will hold back the child’s development by not allowing dorsiflexion to occur. The hinged AFO, in many ways, is very similar to the fixed ankle type.

During the manufacture of the hinged AFO a simple mechanical joint is fitted at the level of the ankle axis and incorporated into the moulding. During manufacture a backstop is also fitted behind the ankle, this prevents plantarflexion. The finished hinged orthosis then allows the required amount of dorsiflexion to occur while preventing all plantarflexion past 90 degrees.

The Hinged AFO also provides medial and lateral stability of the ankle and therefore preventing valgus or varus positioning. The foot plate of the AFO can be made flat or contoured depending on the child’s requirements. The fitting of hinged AFOs can allow for a more natural fluent gait to occur. While allowing the foot and ankle to dorsiflex during other daily activities such as squatting, walking backwards, ascending/descending stairs are also easier.

Foot orthoses

There are times when the child’s condition does not warrant the fitting of an AFO. They may not have the problems of a toe walking gait, but may suffer from general low tone or have some instability of the ankle joint complex. This can lead to problems of balance and a very wide base during walking. The foot and ankle may also tend to fall into a varus or valgus position. When the hindfoot is held in a valgus position the arch of the foot tends to flatten along with it (Overpronation). A varus hindfoot position tends to create a high arched foot (Supination).

In these cases of valgus ankle with overpronation or a varus ankle with supination, the fitting of foot orthoses can be helpful in reducing these unwanted foot and ankle positions and consequently improve balance and posture.

Different types

The orthoses which can help with the problems of ankle and foot instability range from simple supportive footwear, through footwear with adaptations to complex multi-material biomechanical functional foot orthoses. Footwear alone has little effect over any real substantial foot instability, but is useful in offering some improved stability of an unstable ankle when the child starts to walk.

The special footwear has a wide, flat good gripping sole unit with increased stiffening around the ankle and this can help give the child a greater sense of balance. But be aware that the foot itself may still roll around inside the boot unseen and therefore careful fitting of the correct widths and types of boot has to be undertaken.

Adaptations to the footwear can be carried such as medial and lateral wedges to help increase their control over unstable ankles. Foot orthoses can be incorporated into the footwear to improve foot stability and these usually come in the form of insoles with arch support and/or heel cups which are extended up around the heel but finish below the ankle.

Both these types of foot orthosis may have special wedging (Posting), fitted, either to the bottom on the outside (Extrinsic) or built into the orthosis (Intrinsic), when manufactured. The posting or wedging is fitted to induce a correcting force on the heel when the child is weight bearing or walking. These types of foot orthosis are usually made of lightweight thermoplastics and made from a cast of the child’s foot in a corrected position.

It is important to note that the unaffected foot must also be examined and most probably have an orthosis fitted as well. This may not be the same as the opposite leg and may only be a levelling insole but by this it will encourage symmetry and improve balance.

Supramalleolar Orthoses SMOs, (orthoses which finish just above the ankle) or Dynamic Ankle foot orthoses (DAFOs) come in a variety of designs and are very useful in improving medial & lateral stability around the ankle. They offer, however, little control over increased tone or dorsiflexion and plantarflexion. They are therefore ineffective at correcting a toe walking gait. This must be taken into consideration when the child is assessed.

They offer relatively little control of the foot and ankle during the swing phase of gait or when non weight bearing. They only control and stabilise the mid and hind foot when the child is standing or when the affected leg is in a weight bearing position during walking (Stance phase of gait).

What the splint should do

Whatever types of orthosis is recommended or fitted, they share many common design points and try to provide some or all of the features below:

• provide hind foot stability (close moulding around heel)
• provide mid-forefoot stability (medial & lateral extensions. good arch supported)
• control unwanted, exaggerated and abnormal movements
• reduce the effects of increased tone (spasticity)
• promote a stable base
• encourage proximal stability
• built in rear foot/forefoot wedging or posting (valgus or varus)
• toe and Metatarsal support (tone management ?)
• contoured sole plates to assist in foot stabilisation (reduce tone?)
• manufactured from: semi-flexible or rigid materials (polypropylene, polythene etc).

Achieving a normal gait

Orthoses are never an answer in themselves, but in many cases are an extension of the therapist’s arm while away from hands-on active treatment. The goal of orthotic management should be to provide the least amount of hardware possible to encourage and promote the child’s own ability to achieve a normal gait.

It is important that assessment is carried out in a multidisciplinary environment to ensure that the correct orthotic prescription be made. Regular reviews must also be undertaken to ensure continued effectiveness of the orthosis over time during the child’s development and growth.