Foot Orthotics Assessment

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

Introduction

Orthotics is a branch of medicine that deals with the making and fitting of orthotic devices. There are many interchangeable terms for this, a few being foot orthotic/orthosis/insole/shoe insert. Before an orthosis can be prescribed, a comprehensive assessment needs to be conducted to correctly select a device that will meet all the requirements. Selecting an orthotic device can be complicated as there are many aspects that need to be considered aside from biomechanical factors, including comfort and aesthetics to enhance patient compliance.

Three Main Types of Foot Orthoses

1. Off the shelf (OTS) insoles
2. Functional foot orthoses (FFO)
3. Custom moulded total contact insoles (TCI)

Purpose of Foot Orthoses

A foot orthosis is generally referred to as an "externally applied apparatus that can be inserted in a shoe to help support or improve the function of the foot and/or ankle." The main goals of an orthotic device are to improve biomechanics, re-distribute pressure  or to accommodate congenital or acquired deformities. The ultimate aim is to achieve / maintain near-neutral subtalar joint alignment during the gait cycle or the individual's highest functional level.The foot orthosis should:

• Provide support
• Correct, if mobile
• Accommodate if not
• Provide shock absorption
• Re-distribute pressure

Basic Foot and Ankle Anatomy

For a detailed discussion of foot and ankle anatomy, please read these optional pages: Functional Anatomy of the Foot and Functional Anatomy of the Ankle.

Plantar Fascia

• The plantar fascia is a strong, fibrous tissue. Because it is stiff and largely impermeable, it is able to help protect the muscles of the sole of the foot.
• Its origins are deep within the plantar surface of the calcaneus and it fans out across the metatarsal heads. It divides and attaches to the base of the phalanges of each toe.
• During walking, as the toes dorsiflex at push off, the plantar fascia wraps around the metatarsal heads and tightens. This pulls the calcaneus towards the metatarsal heads and in turn maintains the shape of the longitudinal arch and supports the foot to enable propulsion. This is a phenomenon known as the windlass mechanism.

Windlass Mechanism

The human foot is flexible due to its many articulations. However, it needs to be both flexible and rigid to promote normal gait. It is important to remember that the plantar fascia will stretch and recoil at different stages of the gait cycle.

The windlass mechanism was first described by JH Hicks in 1954. Essentially it is: "a one-to-one coupling between metatarsal joint dorsiflexion and medial longitudinal arch rise." Based on an engineering concept of lifting weights via a pulley system, Hicks noted that during dorsiflexion of the toes, the plantar aponeurosis tightens. This draws the metatarsal heads towards the calcaneus, which increases the height of the longitudinal arch. This action occurs naturally at push off in the gait cycle as the toes dorsiflex and the foot becomes stiffer to aid propulsion. During loading and mid stance, the arch will stretch.

Shinohara et al. studied the load-bearing functions of the plantar fascia and intrinsic foot muscles in the windlass mechanism and conclude that the windlass mechanism is predominantly driven by the plantar fascia and the flexor digitorum brevis in a seated posture, whereas it is chiefly influenced by the flexor digitorum brevis during single-leg standing.

Important Joints to Consider for Foot Orthosis

1. Hindfoot
   1. Talocrural joint
   2. Subtalar joint
2. Mid Foot
   1. Tarsometatarsal joint
   2. Calcaneocuboid joint
   3. Talonavicular joint
3. Fore Foot
   1. First metatarsal phalangeal joint

More information on foot and ankle joints is available here.

Terminology Used in Orthotics

Valgus = everted
Neutral
Varus = inverted
Pronation = eversion, abduction, dorsiflexion and medially rotated subtalar joint
Supination = inversion, adduction, plantarflexion and laterally rotated subtalar joint

Purpose of the Human Foot

“[The human foot] enables propulsion through space, adaptation to uneven terrain, absorption of shock, and support of body weight.” However, its structure, function and position leave it exposed to injury. To understand the foot, it is necessary to assess it in non-weight-bearing and weight-bearing positions, and during gait.

Orthotic Foot Ankle Assessment

During a foot and ankle assessment for orthotics selection, you will need to look at:

1. Patient history
2. Range of motion
3. Muscle power
4. Sensation / pain
5. Proprioception
6. Biomechanical analysis
7. Leg length

1. Patient History

• Gait pattern and biomechanical analysis on entrance
  • Type of shoes
  • Assistive devices
• History of underlying conditions, foot problems and the primary problem affecting the individual on consultation.

2. Range of Motion

When considering foot orthosis design, the following range of motion tests should be carried out:

• Active and passive range of motion of the foot and ankle
• Weight-bearing and non-weight bearing assessment

Active and passive movements of the foot and ankle

Active and passive movements of the foot and ankle should include:

• Quick test for the ankle joint = dorsiflexion / plantarflexion
• Quick test for the subtalar joint = pronation/ supination
• Eversion/ inversion
• Abduction / adduction
• Quick test for the metatarsal phalangeal joints = toe flexion/ extension

Non-weight-bearing assessment

• Windlass Test - can be effective for examining dysfunction of the plantar fascia although its specificity has not been proved:
  • Passively extend hallux at the metatarsal phalangeal joint
    • The plantar aponeurosis should tighten and reduce the distance between the calcaneus and metatarsals
    • Please note that the angle of extension to initiate the arch can vary
    • Increases medial longitudinal arch
  • Positive Test: A test is considered positive if passive extension continues to end range or until the patient's plantar fasciitis pain is reproduced
• Medial calcaneus and plantar fascia palpation

• Hallux limitus/rigidus
  • Both affect the windlass mechanism, gait pattern and normal functioning of the foot.
    • Hallux rigidus
      • Very limited dorsiflexion mobility or no movement. There is crepitation with joint mobilisation and pain associated with any movement of the first MTP joint.
    • Hallux limitus
      • Reduced dorsiflexion movement, resulting in decreased range of dorsiflexion at the first metatarsal phalangeal joint.
      • In gait, there is a loss of metatarsal phalangeal joint extension during the second half of the single-support phase, when the weightbearing foot is in maximal dorsiflexion.

3. Muscles of the Foot and Ankle

There are four muscle compartments in the lower leg. The gold standard test for assessing these muscles is the standardised Oxford Scale.

Superficial Posterior Muscle Compartment

Action: Plantarflexion

Muscles: Gastrocnemius, Soleus and Plantaris

Deep Posterior Muscle Compartment

Action: Plantarflexion, adduction and inversion

Muscles: Tibialis Posterior, Flexor Hallicus Longus and Flexor Digitorum Longus

Lateral Muscle Compartment

Action: Dorsiflexion, abduction and eversion

Muscles: Peroneus Longus and Peroneus Brevis

Anterior Muscle Compartment

Action: Dorsiflexion, adduction and inversion

Muscles: Tibialis Anterior, Extensor Hallicus Longus and Extensor Digitorum Longus

See the following pages for more information on the muscle testing of:

• Dorsiflexion
• Plantarflexion
• Eversion
• Inversion

4. Sensation/Pain

Please see page on Sensation, Sensory Examination

5. Proprioception

Please see page on Proprioception, Assessing Proprioception

6. Biomechanical Analysis

It is important to assess the foot both statically and dynamically. This is because the foot is not static during the gait cycle, and most foot problems occur during the gait cycle. It is necessary to look at the whole kinetic chain, including knee and hip/pelvis position, as well as subtalar alignment.

Static Analysis:

This will comprise of the following tests:

• Too many toes test
  • This test is a visual clinical assessment that identifies forefoot abduction, excessive pronation, and posterior tibial tendon dysfunction (PTTD). Viewing the patient directly from behind typically reveals only one and a half to two lateral toes in a normally aligned foot. The presence of three or more visible toes serves as an indicator of structural collapse.

• Jack's test: A test for evaluating the flexibility of a pes cavus (i.e. high arch)

• Windlass test: A test that is effective in examining dysfunction of the plantar fascia by causing a direct stretch on the plantar aponeurosis / fascia

• Coleman Block Test

• Rear foot and forefoot alignment
  • Normal/ideal foot alignment occurs when:
    • Distal 1/3 of leg is vertical
    • Calcaneus is vertical to the supporting surface
    • Plantar forefoot is parallel to the plantar rearfoot
    • Variations from this “normal’ foot alignment (‘intrinsic foot deformities’) lead to abnormal foot functio

Dynamic Analysis: Normal Walking

• Phases of normal walking
  • Heel strike
  • Mid stance
  • Terminal stance
  • Pre swing
  • Swing phase
• Ground clearance is important in swing phase
• Proprioception and balance are important for approximately 40% of the gait pattern where an individual is standing on one leg.

The Supination Resistance Test

The supination resistance test is a very useful test when determining how much force is required from an orthotic device to supinate a foot. It has been shown to be clinically reliable, when tested by a skilled clinician.

Results:

• A high supination resistance score indicates the use of a HIGH arch orthotic.
• A moderate supination resistance score indicates the use of a MODERATE arch orthotic.
• A low supination resistance score indicates the use of a LOW arch orthotic.

Watch the video below to see how the test is conducted:

Root Theory

The root theory was originally developed by Dr. Merton L. Root in the 1950s and 1960s. Alternative terms for his theory found in literature include: “the foot morphology theory,” “the subtalar joint neutral theory,” or the “Rootian theory”. Simply put, the Root Theory is based on a series of static measurements that the author believes can predict kinematic function. In order for the foot to be considered "normal", the subtalar joint (STJ) should be in a neutral position with the midtarsal joint fully locked. This occurs between mid-stance and heel-off during walking. Any deviations from this STJ alignment is considered "abnormal" and would, therefore, result in mechanical dysfunction.

A 2017 study by Jarvis et al. was conducted to investigate foot kinematics between normal and abnormal feet based on Root et al.'s classification. The aim was to assess:

• If there are differences in foot kinematics during gait between feet with / without Root et al.'s structural deformities
• If there is a relationship between the amount of structural deformity and foot kinematic compensations during gait
• If individuals without symptoms achieve the neutral subtalar position during gait

After analysing the results, the authors found that there is no association between the deformities proposed by Root et al. and the differences in foot kinematics during gait.

For more information on the Root theory and other theories of foot function please see the page on Models of Foot Function.

The Kirby Proposal

Dr Kirby was a well known student of Dr Root, and after years of studies, he refuted Dr Root's theory on 11 points.

In summary:

• Kirby disagrees with the theory that the heel vertical position is the most desirable position for the foot to function in and the orthosis to control the foot in, which is one of the fundamental points of the Root Model.
• Root had strong opinions on the type of materials that orthoses should be made out of and often advocated for rigid, unaccommodating materials. Kirby has offered examples where more accommodating materials can be advantageous.
• Root and Kirby disagree on the length of a foot orthosis. Root believed that the orthosis should not extend past the metatarsal necks and conditions distal to this point were unable to be treated with orthotics. Kirby has subsequently achieved good results with treating a plantarflexed third metatarsal.
• Dr. Bill Orien and Dr Root advocated for a list of "Laws of Foot Function", many of which Dr Kirby disagrees with, such as "If a calcaneus is everted by more than two degrees then it will continue pronating until the maximally pronated position of the STJ is reached."
• Dr Kirby also disagreed with theories by John Weed on casting and how it can affect subtalar neutral.

For more detailed information, you can follow Dr Kirby on his Facebook page or his website. Alternatively, you can watch this video if you would like to learn more:

7. Leg Length Discrepancy (LLD)

Number of clinical and imaging modalities exist for assessing leg length discrepancy. The most frequently used clinical techniques are tape measure and standing on blocks. Imaging methods include plain radiography, orthoroentogenogram, scanogram, computed radiography, and ultrasound. Clinician assesses the following:

• Dipping
• Pelvic obliquity
• Retraction
• Scoliosis
• Apparent leg length
• Actual leg length

Additional information:

This video covers an orthotic Biomechanical Assessment: