A Closer Look At Neoteric Biomechanics

Author(s): 
By Dennis Shavelson, DPM

For years, it seems like the $5,000 bunion and pressures from HMOs diverted DPMs’ attention from biomechanics. The emphasis of our education and practices strayed from Root toward Ilizarov and coding. “Gold standard” orthotics cast from foam or “posted to cast” do not generate the pride and acceptance that a Root device once did for podiatry and our orthotic fees are less justified when compared to high-tech, over-the-counter footbeds and custom devices casted by other providers or over the Internet.

The solution is neoteric biomechanics, a school of functional lower extremity biomechanics based on the functional dynamic arches and the vault of the foot. Practicing Functional Foot Typing™ (FFT) allows clinicians to profile feet, before or after developing pathology, into one of 16 functional foot types. After classifying patients, DPMs can educate patients and treat their feet and posture.

After diagnosing patients, one can educate them and treat their specific foot types. Concepts like the inherited nature of foot problems, performance enhancement, pathology and deformity prevention, and improving quality of life become understandable and marketable to physicians and patients. One can prescribe, cast and fabricate functional foot type-specific orthotics, improving results while reducing failures and complications.

Understanding Anatomical Considerations With Neoteric Biomechanics
The foot can be divided into three sections: a rearfoot pillar, a forefoot pillar and the digits. The 33 joints in the foot can either stabilize the bones or move them within ranges of motion. Muscles insert into the bones as tendons and provide leverage, mobility or stability as they contract and expand. The rearfoot and forefoot pillars can function as separate units or they can unite at their apex (or keystone) as an arch to be supportive. In different feet, one or both pillars can be rigid and supportive, flexible and adaptive or any combination of the two. This is why foot typing is so critical before rendering care to any group of patients.

In his pioneering work, Root observed the foot in gait.1,2 His biomechanical theory focuses on subtalar joint (rearfoot) pathology and control. Since Root’s work, advances in functional lower extremity biomechanics have focused on rearfoot control in order to diagnose and treat feet, and the success and failure of their orthotics and biomechanical care is monitored by gait evaluation.3-7

Neoteric biomechanics goes beyond Root because it takes into account that there are so many daily functions that do not involve rearfoot first loading. Consider static stance, backward movement, side to side movement and up and down movement using Root theory, and you will begin to see where it needs upgrading. Neoteric biomechanics allows one to diagnose and treat patients for living, not only as they move forward from point A to point B.

Root’s followers take a subtalar neutral non-weightbearing cast and then post the rearfoot in varus, rarely adding any modifications or postings to the forefoot of their orthotics. This technique often fails clinically due to the inherent variations of feet and their myriad demands. Neoteric biomechanics expands the diagnostic and treatment capabilities of practitioners of biomechanics by using language and concepts that are teachable and easily understood by the public and the medical community.

What Are The Key Tenets Of Neoteric Biomechanics?
Historically, there have been attempts at profiling and classifying feet for foot type-specific diagnosis and treatment. The low, medium and high arch types, the Greek foot, the French foot and the Morton’s foot as well as Hiss’s classification system for feet have failed to achieve mainstream recognition and application.8 In Valmassy’s 1996 text on biomechanics, Scherer wrote a chapter introducing a classification system for typing feet into one of nine foot types.9 This system served as the seedling for neoteric biomechanics. The Scherer classification system has been modified and upgraded into a system known as Functional Foot Typing, which has been accepted for U.S. patent consideration.

The tenets of neoteric biomechanics emphasize the need for maximum balance and support of feet at all times in order to allow greater, healthier function of feet in a closed chain. The tenets of neoteric biomechanics are as follows:
• The vault of the foot is inherently weak and needs additional support.
• The rearfoot pillar needs to be balanced to the three body planes.
• The forefoot pillar needs to be balanced to the three body planes.
• The rearfoot and forefoot pillars need to be balanced to each other.
• The foundational area of the bases of the two pillars of any arch should be equal.
• The two feet need to be balanced to each other.

Key Insights On The Dynamic Arches Of The Foot And The Vault Of The Foot
In neoteric biomechanics, the paradigm for balancing and stabilizing feet is called the “centering theory of lower extremity biomechanics.” This theory emphasizes the interrelationship between the dynamic arches of the foot and the vault of the foot.
In the human foot, there are two distinct longitudinal dynamic arches, medial and lateral, and one critical transverse dynamic arch.

These arches provide shock absorbency, functional capability and support for the foot, and posture by changing from rigid supporters to flexible adaptors at various times during the weightbearing day. Together, they form the sides and roof of “the vault of the foot.”
When it comes to the lack of natural support the dynamic arches fail to provide to the vault of the foot, one can supplement this by inserting a centering orthotic under the foot.

In regard to the dynamic arches of the foot, which are inherently unstable, be aware of their following properties.
• The pillars of the dynamic arches of the foot are not symmetrical.
• The bones are of different size, shape and density.
• The apex, where the arches meet, is off-center.
• The foundational pillar areas of the base of each of the dynamic arches are unequal.
• The pillars of the dynamic arches are not balanced.
• The pillars that form the dynamic arches are unbalanced to each other.
• The two feet are not balanced to each other.

If the dynamic arches of the foot were architectural (composed of symmetrical pillars, a centered keystone and proportional bones), they would support very well but they would not flex and perform the functions for daily life. Therefore, our feet have sophisticated movement and function but inherent weakness when it comes to support. As a result, predictable overuse syndromes and foot and postural breakdown develop.

How The Functional Foot Typing System Works
The FFT system is based upon two positional measurements of the rearfoot and two positional measurements of the forefoot that give diagnostic information about the state of the dynamic arches of the foot and the vault of the foot. The rearfoot measurements are the subtalar supinatory end range of motion (SERM) position and the subtalar pronatory end range of motion (PERM) position. The forefoot measurements are the forefoot supinatory end range of motion (SERM) position and the forefoot pronatory end range of motion (PERM) position.

The subtalar SERM position is the open chain position the subtalar joint assumes with reference to a bisection of the lower one-third of the leg after applying a strong inversion force upon the calcaneus until it can no longer move. For FFT classification, there are two possibilities (inverted or everted) for the subtalar SERM position.

The subtalar PERM position is the open chain position that the subtalar joint assumes with reference to a bisection of the lower one-third of the leg after applying a strong eversion force on the calcaneus until it can no longer move. For FFT classification, there are three possibilities for the subtalar PERM position — inverted, vertical or everted.

The forefoot SERM position is the open chain position that the first metatarsal assumes with reference to the locked fifth metatarsal after applying a strong plantarflexory force downward upon the first metatarsal from above until it can no longer move. For FFT classification, there are two possibilities (dorsiflexed or plantarflexed) for the forefoot SERM position.

The forefoot PERM position is the position that the first metatarsal assumes in an open chain with reference to the locked fifth metatarsal after applying a strong dorsiflexory upward force upon the first metatarsal from below until it can no longer move. For FFT classification, there are three possibilities for the forefoot PERM position — dorsiflexed, in line with the fifth metatarsal or plantarflexed.

In the FFT system, the subtalar SERM position and the subtalar PERM position diagnose a specific rearfoot type, and the forefoot SERM position and the forefoot PERM position diagnose a specific forefoot type. After determining the rearfoot type and the forefoot type, every foot can be assigned a Functional Foot Type.

In the FFT system, there are four rearfoot and four forefoot types: rigid, stable, flexible and flat. When one plots the four rearfoot types longitudinally and plots the four forefoot types horizontally, there is a 16-box matrix with each box representing a functional foot type (see “Understanding The Functional Foot Typing System” below).

Diagnosing The Functional Rearfoot And Forefoot Types
Comparing the subtalar SERM and the subtalar PERM positions of the subtalar joint allows one to classify all feet into one of four functional rearfoot types.
The rigid rearfoot type has an inverted subtalar SERM and an inverted subtalar PERM.
The stable rearfoot type has an inverted subtalar SERM and a perpendicular subtalar PERM.
The flexible rearfoot type has an inverted subtalar SERM and an everted subtalar PERM.
The flat rearfoot type has an everted subtalar SERM and an everted subtalar PERM.

In the same vein, comparing the forefoot SERM position and the forefoot PERM position of the forefoot allows the clinician to classify all feet into one of four functional forefoot types.

In the rigid forefoot type, the forefoot SERM places the first metatarsal below the fifth metatarsal. The forefoot PERM places the first metatarsal below the fifth metatarsal.

In the stable forefoot type, the forefoot SERM places the first metatarsal below the fifth metatarsal. The forefoot PERM places the first metatarsal in line with the fifth metatarsal.

In the flexible forefoot type, the forefoot SERM places the first metatarsal below the fifth metatarsal. The forefoot PERM places the first metatarsal above the fifth metatarsal.

In the flat forefoot type, the forefoot SERM places the first metatarsal above the fifth metatarsal. The forefoot PERM places the first metatarsal above the fifth metatarsal.

A Guide To The Characteristics Of The FFTs
Each FFT is associated with a set of features that help define that FFT. These include an open and closed chain presentation, forefoot lesion pattern, X-ray presentation, shoe wear, foot deformities, foot pain and fatigue syndromes, and postural pain and fatigue symptoms. Although FFTs share some characteristics, each FFT has a unique profile. If the clinician is given a set of foot typing characteristics, he or she can diagnose the FFT.

Open and closed chain presentation. Functional foot types have specific open and closed chain presentations. The lateral and dorsoplantar views, weighted and non-weighted, allow for foot type diagnosis. Changes in arch height, rearfoot pillar and/or forefoot pillar splay, the absence or presence of hammertoes and the absence or presence of metatarsocuneiform exostoses reflect foot type-specific qualities.

Forefoot lesion pattern. Functional foot types develop a specific forefoot lesion pattern in areas of pressure, deformity and increased weightbearing. Foot type-specific lesions occur in the medial column, the lateral column and the digits.

X-ray presentation. Functional foot type specific X-ray changes reflect areas of pressure, deformity and increased weight. AP and lateral closed chain (weightbearing) X-rays are standard and a lateral contact open chain X-ray is helpful in the flexible foot types.

Foot type-specific X-ray characteristics include periosteal changes reflecting metatarsal weight imbalances, FFT specific deformities, sinus tarsi changes, variations in clinical inclination angle, CYMA line changes, talocalcaneal angle changes, forefoot angle abnormalities and dorsal metatarsocuneiform changes.

Shoe sole wear. Functional foot types show specific shoe sole wear in areas of pressure, deformity and increased weight. One may note rearfoot sole wear, midfoot sole wear or forefoot sole wear.

Pedal deformities. Functional foot type specific deformities develop in areas of pressure, deformity and increased weight. These deformities may include hammertoes, bunions, bunionette formation, dorsal metatarsocuneiform bumps, hallux interphalangeal deformity and/or Haglund’s deformity.

Associated foot and postural problems. Functional foot type specific foot and postural problems develop in areas of pressure, deformity and increased weight. Problems may include plantar fasciitis, posterior tibial tendon dysfunction, flexor hallucis longus, functional equinus, postural fatigue, knee problems, hip problems and/or lower back problems.

Pertinent Pearls On FFT Orthotics And Casting
In regard to FFT orthotics, clinicians can cast, prescribe, fabricate and dispense them for specific foot types. Each FFT has particular casting techniques and prescription customizations. FFT orthotics are modified UCBL devices composed of a thermoplastic shell fabricated from a positive model and poured from a negative corrected cast plaster or fiberglass cast. They have a deep heel seat and modified medial and lateral flanges. In addition to rearfoot posts, they have forefoot postings and modifications. FFT orthotics have higher arches, are shorter in length, narrower and have aggressive forefoot posting compared to current standards.

There are several casting techniques for FFT orthoses.
Rearfoot SERM-PERM balancing. The practitioner moves the cast from an inverted position to vertical under the lower one-third of the leg.
Lateral dynamic arch correction. The DPM places upward force under the fifth or fourth and fifth metatarsal heads, locking the lateral dynamic arch, and stopping at a point when this begins to influence the rearfoot.
Rearfoot vault enhancement. The practitioner grasps the back of the heel of the foot with the palm and the fingers. Utilizing the thumb at the plantar surface of the heel, one exerts an upward force, elevating the calcaneus and expanding the rearfoot vault.
Forefoot vault enhancement. Exert a downward force at the top of the first metatarsal head until end range of motion. Then apply an upward force under the second to fourth metatarsals just proximal to the metatarsal heads in order to expand the forefoot vault.
Hammertoe correction. Place the second finger across the bases of the toes dorsally and exert a downward force until the toes are in line with the metatarsal heads, and not knuckled.

Inside Insights On Functional Foot Type Orthotic Casting
The following are suggestions for casting the various foot types.
For rigid rearfoot types, utilize standard “Root” neutral casting technique. For stable rearfoot types, utilize SERM-PERM balancing and rearfoot vault enhancement techniques. For flexible rearfoot types, utilize SERM-PERM balancing and rearfoot vault enhancement techniques. For flat rearfoot types, utilize standard “Root” casting technique.
Apply the lateral longitudinal arch correction technique to all casts, regardless of the functional foot type.
For rigid forefoot types, utilize the standard “Root” casting technique. For stable forefoot types, utilize the forefoot vault enhancement technique. For flexible forefoot types, utilize the forefoot vault enhancement technique. For flat forefoot types, utilize the standard “Root” technique.

Utilize hammertoe correction technique for all casts, regardless of the functional foot type.

How To Prescribe FFT Orthotics
A foot type-specific prescription accompanies the negative cast models to be fabricated. Consider the following prescribing techniques.
Rearfoot posting. Use angulated materials and lifts that balance the rearfoot to the weightbearing surface. Rearfoot posts can be varus, vertical or valgus.

Forefoot posting. Use angulated materials that balance the forefoot to the weightbearing surface. Forefoot posts can be varus or valgus or vertical lifts or bars.

Forefoot ray cutouts. Remove material from the FFT orthotic shell to allow specific bones to drop, thus enhancing the forefoot vault and leveraging slack tendons.

In regard to FFT-specific prescription guidelines, one should keep the following pointers in mind.

For rigid rearfoot types, utilize a varus rearfoot post. Add lift to the rearfoot post as tolerable to the inside of the shoe.

For stable rearfoot types, utilize a vertical rearfoot post. For flexible rearfoot types, utilize a vertical rearfoot post. For flat rearfoot types, utilize a valgus rearfoot post.

For rigid forefoot types, utilize a 1-4 valgus forefoot post. For stable forefoot types, utilize a 2-5 varus forefoot post with a first ray cutout. For flexible forefoot types, utilize a 2-5 varus forefoot post with an aggressive first ray cutout. For flat forefoot types, utilize a 1-5 varus forefoot post.

In Conclusion
Although the followers of neoteric biomechanics are enjoying clinical success, it is the hope of the author to stimulate outcome studies that go beyond anecdotal findings. 

Editor’s Note: For a related article, see “Emerging Concepts In Podiatric Biomechanics” in the December 2006 issue.

 

 

 

 

 

 

References:

1. Root ML. An approach to foot orthopedics. J Am Pod Assoc 54(2):115-118, February 1964.
2. Root ML, Orian WP, Weed JH. Clinical biomechanics: normal and abnormal function of the foot, volume 2. Los Angeles: Clinical Biomechanics, 1977.
3. Blake RL, Baitch SP, Finegan PL, Senatore J. Biomechanical analysis of running with 25 degree inverted orthotic devices. JAPMA 81(12):647-652.
4. Kirby KA. The medial heel skive technique: improving pronation control in foot orthotics. JAPMA 82(4):177-188.
5. Dananberg H. Can in-shoe pressure analysis reinvent orthotics. Podiatry Today 14(2):27-28, 2001.
6. Sol N. Using in-shoe pressure analysis for orthotic accuracy. Curr Pedorth 6:10-31, Aug/Sept 2001.
7. Nester CJ, Van Der Linden ML, Bowker P. Effect of foot orthoses on the kinematics and kinetics of normal walking gait. Gait Posture 17:180-187, 2003.
8. Hiss JM. Classifying feet. In: Functional foot disorders, third ed. Los Angeles: Oxford Press, 1949.
9. Scherer PR, Morris JL. The Classification of Human Foot Types, Abnormal Foot Function, and Pathology. In: Valmassy RL. Clinical Biomechanics of the Lower Extremities. St. Louis: Mosby; 1996. p. 85-93.

 

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