Orthotic Design for Foot Pathologies

Original Editor - Carin Hunter based on the course by Donna Fisher Top Contributors - Carin Hunter, Jess Bell, Kim Jackson, Stacy Schiurring, Tarina van der Stockt, Vidya Acharya and Lucinda hampton

Commonly Used Types of Orthotics

1. Ankle Foot Orthoses

The main function of an Ankle Foot Orthosis (AFO) is to maintain the foot in a plantigrade position. This provides a stable base of support that facilitates the function and can also reduce tone in the stance phase of the gait. The AFO supports the foot and prevents foot drop during swing phase. When worn at night, a rigid AFO may prevent contracture. AFOs provide a more energy efficient gait. The brace should be simple, light but strong. It should be easy to use. Most importantly it should provide and increase functional independence.

For more information on this, please see Introduction to Ankle Foot Orthoses.

2. Functional Foot Orthosis

A Functional Foot Orthosis (FFO) is designed to realign the joints and bones in the foot in order to decrease stress within the knee, ankle or foot. Patients may require a single FFO or a pair of FFOs.

Various techniques are used when designing an FFO. One commonly used technique is to create a Heel Skive. This is an intrinsic (i.e. within the heel cup) flat spot that creates an angled floor under the foot. This angled floor can be put anywhere within the heel cup.

• Medial Heel Skive: A small portion of the negative mould of the orthosis is removed on the medial aspect of the plantar heel. This creates a varus wedge within the heel cup of the final insole. The force applied is shifted laterally, resulting in supination/inversion and improved pronation control.

• Lateral Heel Skive: A small portion of the negative mould of the orthosis is removed on the lateral aspect of the plantar heel. This creates a valgus wedge within the heel cup of the final insole. The force applied is shifted medially, resulting in pronation/eversion.

3. Total Contact Insoles (TCI)

A Total Contact Insole (TCI) is a custom-designed foot orthotic which aims to redistribute a person’s weight evenly over their foot. It is specifically designed for each individual, based on a model of an individual's foot, and after extensive examination. It offers support through the shape and density of materials. A TCI has better shock absorption due to the materials used in the design than an FFO. A TCI is custom-made, usually made from Ethyl Vinyl Acetate (EVA). It can be a high, medium or low density material. They are designed from a cast, foam box or scan and manufactured in a workshop or lab. While they can be bulky, they are designed to support, correct and accommodate a foot with good shock absorption.

4. Off the Shelf Insoles (OTS)

An Off the Shelf (OTS) insole is generally in a neutral position with a standard arch support. The insole is made of a material, which has different densities. It is low profile and has good shock absorption. These insoles offer minimal correction with no accommodation of deformity. But they are often a good starting point.

Non-Pathological Foot

1. No underlying condition
2. Normal foot structure
3. Pain
4. Musculoskeletal issues
5. Trauma
6. Tendon dysfunction

Congenital Paediatric Problems

1. Flexible Pes Planus
2. Accessory Navicular
3. Vertical talus
4. Cavus Foot

Flexible Pes Planus

Pes Planus in a toddler

Pes planus, also known as flat foot, is the loss of the medial longitudinal arch of the foot, heel valgus deformity, and medial talar prominence. In lay terms, it is a fallen arch of the foot that causes the whole foot to make contact with the ground surface. The deformity is usually asymptomatic and tends to resolves spontaneously in the first decade of life. However, occasionally it progresses into a painful rigid form, which causes significant disability. All children have flat feet at birth and noticeable foot arches are not usually seen until approximately 3 years of age.

There are generally two forms of pes planus; flexible flat foot and rigid flat foot. Flexible flat foot is when the arch of the foot is intact on heel elevation and non-weight bearing, but disappears when standing on the foot. Rigid flat foot is when the arch is not present in either heel elevation or weight bearing.

Treatment: Off the Shelf (OTS) insoles

Tests: Jack's Test

Common Problems in the Adult Non-Pathological Foot

1. Adult Acquired Flat Foot (AAFF)
   1. Most common cause is Posterior Tibial Tendon Dysfunction
2. Posterior Tibial Tendon Dysfunction
3. Plantar Fasciitis
   1. Inflammation of the plantar fascia
   2. Often tested using the Windlass test
   3. A common symptom is pain, particularly pain in the morning
   4. Can be treated with night-time splints
4. Hallux Limitus
   1. Defined by the degree of flexibility of the first metatarsal phalangeal joint
   2. To assess try to encourage flexion by increasing plantarflexion of the first ray
5. Hallux Rigidus
   1. Defined by the degree of flexibility of the first metatarsal phalangeal joint
   2. To assess try to encourage flexion by increasing plantarflexion of the first ray
6. Metatarsalgia
7. Heel Spurs
   1. Patients usually present with specific heel pain
   2. An orthotic should off load the area
8. Claw Toe or Hammer Toes
9. Arthritis
   1. An orthosis should offer shock absorption and support while off loading the area
10. Morton's Neuroma
    1. Mulder’s test

Posterior Tibial Tendon Dysfunction

Posterior tibial tendon dysfunction (PTTD) occurs when the posterior tibial tendon becomes inflamed or torn. As a result, the tendon may not be able to provide stability and support for the arch of the foot. PTTD is characterised by the degeneration of this tendon and it is progressive if not treated. It can also be associated with a tear or stretching of the spring ligament. The spring ligament functions as a static restraint of the medial longitudinal arch. It supports the head of the talus from planter and medial subluxation against the body weight during standing. Posterior tibial tendon dysfunction is typically a slow onset condition mainly affecting women older than 40 years of age.

• Risk factors:
  • Obesity
  • Hypertension
  • Diabetes
  • Steroid use
  • Seronegative arthropathies (eg ankylosing spondylitis)
• Signs and symptoms:
  • Pain and swelling around the medial ankle
  • Difficulty mobilising
  • Exacerbation of an existing limp
  • Tenderness along the course of the tendon
  • A change in the shape of the foot
  • The heel is everted
  • The arch is collapsed
  • There is reduced flexibility

• Test:
  • “Too many toes” test when feet are viewed standing from behind
  • Difficulty performing a single heel raise and heel remains in an everted position

• 5 stages

1. I - Acute
2. II - Flexible, requires FFO
3. III - Fixed, requires Arizona boot AFO
4. IV - Chronic, requires AFO
5. V - Chronic, requires surgery

• Treatment: The treatment plan for posterior tibial tendon tears varies depending on the flexibility of the foot.

Posterior Tibial Tendon Orthotic Prescription

• Goal
  • To reduce the excessive pronatory forces acting across the subtalar joint (STJ)
• Design
  • The orthoses must control pronation with significant surface area contacting the foot. The modifications should increase supinatory torque across the STJ axis.
  • Usually constructed from a Polypropylene Shell, which is semirigid
  • It will have a deep heel cup, which increases the surface area medial to the STJ axis applying the supinatory torque
  • It will also have a Medial Heel Skive of approximately 4mm or 6mm. The medial heel skive increases force medial to the STJ axis to reduce excessive STJ pronation and heel eversion.

• Measurement
  • The foot is measured with a cast, foam box or scan to capture the shape of foot
  • It is modified intrinsically in a workshop or lab
  • Extrinsically posted adaptions can be added
  • They usually have a low profile and are full, 3⁄4, court or sports design
  • They often have limited shock absorption or accommodation

• Prescription
  • Often the main issue revolves around the part of gait cycle that is affected
  • Pes planus requires arch support
  • Subtalar joint rotation requires wedging
  • Problems higher up commonly require compensation

• Principle of Orthotic Design
  • Always look at the position of heel/forefoot and subtalar joint rotation
  • Medially rotated subtalar joint
    • Increased pronation moment/decreased supination moment
    • Re-balance by moving ground reaction forces medially, increasing supination moment, reducing medial rotation
  • Laterally rotated subtalar joint
    • Increased supination moment, decreased pronation moment
    • Re-balance by moving ground reaction forces closer to subtalar joint, to increase pronation moment of ground reaction forces

Hallux Limitus

1. Functional Foot Orthosis (FFO)
   1. An arch fill
      1. This will increase or decrease arch support
   2. First ray /first metatarsal cut out
      1. This will allow the first ray to plantarflex, which is key for normal gait and the windlass mechanism. It is not always necessary if a Corrected Cast is used.
   3. Reverse Morton's Extension
      1. Extra material is added under the second to fifth metatarsal heads to allow plantarflexion of the first ray
   4. Morton's Extension
      1. Extra material is added under just the first metatarsal head to increase plantar pressure and flex the first metatarsal head. It can be rigid or flexible and is useful in treating Hallux Rigidus to reduce painful movement and protect stiff joints.

Non-Pathological Foot - Injury /Trauma

1. Medial tibial stress syndrome, more commonly known as Shin splints
2. Overuse injury of the Tibialis Posterior or Tibialis Anterior
   1. Orthotics should support, reduce overuse by balance, and offer shock absorption
3. Inversion injury or lateral ankle sprain
   1. Most commonly injured are anterior and posterior talofibular ligament and calcaneofibular ligament. A lateral wedge to increase pronation for stability is recommended
4. Lisfranc injury
5. Achilles tendon injuries
   1. Orthotics should relieve the tendon with a heel post

Common Pathological Foot Conditions

Pathological foot conditions are commonly broken up into three categories: neurological, motor and sensory. A pathological condition is often more complex to treat as all joints or muscles are affected. On assessment, you should look at hip and knee position as well. Feet and ankles will adapt to the ground to support structures higher up and compensate for bony abnormalities.

1. Neurological

1. Stroke
2. Multiple Sclerosis
3. Cerebral Palsy

2. Motor

1. Ataxia
2. Dystonia
3. Pathological Foot

3. Sensory/ Neuropathy

1. Diabetes
   1. Often present with sensory and neuropathic issues, pressure areas and posterior tibial tendon dysfunction
   2. An orthotic should off-load a diabetic ulcer, with a toe filler being used for an amputation
2. Charcot Marie Tooth
   1. Orthotic insoles are often prescribed
3. Down Syndrome
4. Autism Spectrum Disorder

When dealing with pathological foot conditions there are four common deformities encountered when creating on orthosis:

1. Valgus deformity
2. Varus deformity
3. Forefoot deformity
4. Hindfoot deformity

Valgus Deformity

• Rocker Bottom Foot
  • An orthotic device should accommodate and support the foot
• Hyper-mobility
  • Initially advise an off the shelf orthosis. If this does not work for paediatric hypermobility, then a custom device can be constructed
• Escape Valgus
  • This is a compensatory movement, usually to accommodate for a tight Achilles tendon (TA). Can be caused by a lateral bow-stringing of the TA or the Achilles tendon may be malaligned relative to the calcaneus. There is a shortening of the gastrocnemius or soleus and the heel pulls into valgus/eversion and over-pronates the midfoot. It can alter the foot structure and result in long-term problems.

Varus Deformity (Cavus)

• Cavo varus
  • This often presents as weakness in tibialis anterior and peroneal brevis (dorsiflexion and eversion), tight plantar fascia, and an over-active peroneus longus which pulls the first ray into plantarflexion
  • This can be caused by a plantarflexed first ray (forefoot-driven), a deformity of the hindfoot (hindfoot-driven), or a combination of both
  • For more information, please follow this link: Cavovarus Foot in Pediatrics & Adults
• Congenital talipes equinovarus
  • Often referred to as 'club-foot'
  • It is defined as a deformity characterised by complex, malalignment of the foot involving soft and bony structures in the hindfoot, midfoot and forefoot. The foot is usually fixed in adduction, in supination and in varus. At the subtalar joint, the foot is held in a downward pointing position. The foot affected by clubfoot is often shorter, and the calf circumference is usually less than the unaffected foot.
• Hereditary motor and sensory neuropathies (HMSN)
  • Also known as Charcot–Marie–Tooth disease (CMT)
  • It is an inherited disease of the nerves that presents as a progressive weakness and numbness often more pronounced in the legs than the arms
  • For more information please see Hereditary Motor Sensory Neuropathy

Forefoot versus Hindfoot Deformity

• Gait
  • In midstance, plantarflexion of the first ray leads to a compensatory varus heel, lateral rotation of STJt and reduced shock absorption
  • During heel-off (terminal stance), the plantarflexed first ray causes a supination of the forefoot that increases the varus deformity of the hindfoot
• In hindfoot-driven cavo-varus deformity, the subtalar joint may compensate for varus deformities above the ankle joint
• Overload of the lateral soft tissue structures (eg, lateral ligament complex, peroneal tendons) and degenerative changes (eg, medial ankle osteoarthritis, midfoot arthritis) may occur over time
• Lateral forefoot wedge used
• Assess with Coleman Block Test

Summary

• The foot anatomy is a complex mechanism that allows standing, balance, walking, running, jumping, and responding to a lifetime of external factors.
  • Assessment will include history taking and passive, static and dynamic examinations
  • There is no one correct or standard solution to address impairments of the foot
  • It is important to educate patients on orthoses
  • Orthotics are most effective when used in combination with other multidisciplinary treatments

Physiopedia Pages to Further Your Knowledge

Biomechanics for Cerebral Palsy Orthotics