Orthotic Design for Foot Pathologies

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

Commonly Used Types of Orthotics

1. Ankle Foot Orthoses (AFO)

The AFO is the basic orthosis in CP and is a crucial piece of equipment for many children with spastic diplegia. The main function of the AFO is to maintain the foot in a plantigrade position. This provides a stable base of support that facilitates the function and also reduces 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 (FFO)

A functional foot orthosis is designed to realign the joints and bones in your foot. This goal of this is to decrease stress stress within your knee, ankle or foot. You may be given a single FFO or a pair of FFO's.

There are varies techniques used when designing an FFO. One commonly used technique is to create a Heel Skive. This is an intrinsic (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 (Kirby): This technique is when a small portion of the orthosis is removed on the medial aspect of the plantar heel. This creates a varus wedge within the heel cup. The force applied is shifted laterally, resulting in supination/inversion and improved pronation control.
• Lateral Heel Skive: This technique is when a small portion of the orthosis is removed on the lateral aspect of the plantar heel. This creates a valgus wedge within the heel cup. 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 with the aim of redistributing a person’s weight evenly over their foot. The design is unique to each individual and is based on an extensive examination and often a model made of the patient’s foot. 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.

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
   1. Congenital 12% pop., pain, redness, PTTD
3. Vertical talus
   1. Congenital, may have other conditions, rocker bottom foot
4. Freiberg's Disease
   1. Forefoot pain, stiffness, 2nd MPT, rare
5. Cavus Foot
   1. High arch, CTEV

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 caused the whole foot to make contact with the surface the individual is standing on. The deformity is usually asymptomatic and resolves spontaneously in the first decade of life, or occasionally progresses into a painful rigid form which causes significant disability. All at birth has flat feet and noticeable foot arch are seen at around the age of 3years.

It is of two forms; flexible flat foot and rigid flat foot. When the arch of the foot is intact on heel elevation and non-bearing but disappears on full standing on the foot, it is termed flexible flat foot while rigid flat foot is when the arch is not present in both heel elevation and weight bearing.

Tests: Jacks Test, arch recreates

Treatment: Off the Shelf (OTS) Insoles

1. Generally standard neutral position
2. Standard arch support
3. Different densities
4. Low profile
5. Shock absorption
6. Minimal correction
7. No accommodation of deformity
8. Good starting point

Adult Non-pathological Foot – Common Problems

1. Adult Acquired Flat Foot (AAFF)- most common caused by Posterior Tibial Tendon Dysfunction
2. Posterior Tibial Tendon Dysfunction
3. Plantarfasciitis
   1. Inflammation of plantar fascia
   2. Windlass test +/-, common symptoms, pain , am, n/splints
4. Hallux rigidus/limitus
   1. Flexibility of 1 st MTP
   2. Test, to ax limitus or rigidus, try to encourage flexion by inc p/f 1st ray
5. Metatarsalgia
   1. Prominent bony structures, pain
6. Morton's Neuroma
   1. Mulder’s test
7. Heel spurs
   1. Specific heel pain, treat with off load device
8. Claw/ hammer toes
   1. Fixed/mobile
   2. pain
   3. callousing
   4. shoes
9. Arthritis
   1. shock absorption, support off load

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 characterized by the degeneration of this tendon and is progressive if not treated. It can also be associated with tear or stretching of the spring ligament. The spring ligament functions as 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 characteristically is 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 mobilizing
  • Exacerbation of an existing limpTenderness along the course of the tendon
  • A change in the shape of the foot
  • The heel is everted
  • The arch collapsed
  • Flexibility reduced

• Test:
  • “Too many toes” test when feet are viewed standing from behind
  • Difficulty performing a single heel raise and heel remains in 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) axis.
• Design
  1. The orthoses must control pronation with significant surface area contacting the foot. The modifications should increase supinatory torque across the STJ axis.
  2. Polypropylene Shell - semirigid
  3. Deep Heel Cup
  4. The deep heel cup increases surface area medial to the STJ axis applying a supinatory torque
  5. Medial Heel Skive – 4mm or 6mm
  6. The medial heel skive increases force medial to the STJ axis to reduce excessive STJ pronation and heel eversion.
• Measurement of FFO
  1. Cast, foam box, scan to capture shape of foot
  2. Modify intrinsically in w/shop or lab
  3. Extrinsically posting/adaptions can be added
  4. Often off site manufacture
  5. Low profile- full, 3⁄4, court, sports
  6. Limited shock absorption or accommodation
• Prescription of FFO
  1. Based on Exam/assessment
  2. Main issue- part of gait cycle, ie MS or push off
  3. Determine what mechanism for problem
  4. Pes planus, arch support
  5. Subtalar joint rotation, wedging
  6. Problems higher up, compensation
  7. Weakness/tightness, hips, knees
• Principle of Orthotic Design
  1. Position of heel/forefoot and subtalar joint rotation
  2. Medially rotated subtalar joint
  3. Increased pronation moment/ decreased supination moment
  4. Rebalance by moving GRF medial, increasing supination moment, reducing medial rotation
  5. Laterally rotated subtalar joint
  6. Increased supination moment, decreased pronation moment
  7. Rebalance by moving ground reaction forces closer to subtalar joint, to increase pronation moment of ground reaction forces

Hallucis Limitus

1. Functional Foot Orthosis (FFO)
   1. Arch Fill – can increase or decrease arch support, be careful.
   2. 1st ray /1st met cut out- allows the 1st ray to plantarflex- key for normal gait, windlass. Not always necessary if corrected cast used- FnHl, Plantar flexed 1st ray
2. Functional Foot Orthosis (FFO)
   1. Mortons extension ( not to be confused with Mortons neuroma)
   2. Extra material added under 1st met heads only to increase plantar pressure and flex 1st met head, Can be Rigid or flexible useful in treating HR, to reduce painful mvt, protect stiff joint also shoe mod can help
3. Reverse- extra added under 2-5 to allow plantarflexion of 1st ray-
4. Hallucic Rigidus, allows p/flexion of 1st ray and increases flexion MTP, windlass.

Non-pathological Foot - Injury /Trauma

1. Shin splints/ Medial Tibial Stress Syndrome
2. Overuse injury, Tibialis Posterior/Tib ant-
   1. Support, reduce overuse by balance, shock absopt and rest
3. Inversion injury/Lat ankle sprain-
   1. Ant/post TaloFibL, CalcFibL- lateral wedge, increase pronation to stabilise.
   2. Eversion – Deltoid, less common
4. Lisfranc Injury/Trauma
5. Achilles Tendon injuries-
   1. relieve with heel post, stretch

Common Pathological Foot Conditions

Pathological foot conditions are commonly broken up into 3 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. Cerebral Palsy

1. Stroke
2. Multiple Sclerosis

2. Motor

1. Ataxia
2. Dystonia
3. Pathological Foot

3. Sensory/ Neuropathy

1. Diabetes
   1. Sensory
   2. Neuropathic issues
   3. Pressure areas
   4. Posterior tibial tendon dysfunction
   5. Off -Loading Diabetic Ulcers
   6. Toe fillers amputation
2. Charcot Marie Tooth
   1. Orthotic Insoles
3. Down Syndrome
4. Autism Spectrum Disorder

When dealing with pathological foot conditions there are four common deformities we encounter 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 it does not work for paediatric hypermobility then a custom device can be constructed
• Escape Valgus
  • This is a compensatory movement, usually to accommodate for tight Achilles tendon. Can result as a lateral bow-stringing of the TA or just that the Achilles tendon is mal-aligned in relation to the calcaneus. There is a shortening of the gastrocnemius or soleus and the heel pulls into valgus/eversion and over pronates mid foot. It can alter the foot structure and can result in long term problems.

Varus Deformity (Cavus)

• Cavo Varus
  • This often presents as weakness in tibialis anterior & peroneal brevis ( which dorsiflex and evert), tight plantar fascia, over-active peroneus longus which pulls 1st ray into plantarflexion.
  • This can be the result of a plantar flexed 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 characterized 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 v Hindfoot Deformity

• Gait
  • In midstance, plantarflexion of the first ray leads to a compensatory varus heel, supination 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.
• Coleman Block Test

• Lateral Forefoot Wedge

Summary

• The anatomy of the foot is a complex mechanism to allow standing, balance, walking, running, jumping, lifetime of external factors
  • Assessment will include history, passive, static and dynamic
  • There is no one correct or standard solution, watch, listen and learn
  • Patient and clinical education
  • Orthotics in combination with other MDT treatments
• In summary

Physiopedia Pages to Further Your Knowledge

Orthotics in Cerebral Palsy

Biomechanics for Cerebral Palsy Orthotics