Foot Posture Theories

It is generally agreed upon that in order to determine "abnormal" form, posture, or structure in the foot, a "normal" form, postural, and structural baseline must first be determined. Past and present foot posture theories are an attempt to create a standardized basis for evaluation, casting, and fabrication techniques.

Subtalar Joint Neutral Position Theory
In 1977, Merton Root, DPM, published a textbook in which he posited his Subtalar Joint Neutral (STJN) Theory. STJN has since been the "Gold Standard" and is thought of as the traditional approach to orthotic intervention. However, there are many controversies as to the accuracy and efficacy of this approach and many contemporary practitioners prefer one of the alternative theories listed below. Root described STJN as the position at which the ratio of calcaneal inversion to eversion is 2:1 and also the position the STJ reaches immediately after heel strike and again at 50% through the stance phase of gait. Using a protractor to measure STJ inversion/eversion, Root devised a formula that states that the STJN is the sum of the degrees of inversion plus the degrees of eversion, divided by 3, minus the degrees of eversion.


 * {(inversion + eversion) / 3 } - eversion = STJN

Today, STJN position is generally accepted as the position when the STJ is neither pronated or supinated. At STJN, there is maximum congruity of the joint surfaces on the medial and lateral sides. This would minimize the tension in the ligamentous restraints and allow for an equalization in inversion/eversion caused by passive muscle tension. Root held that the midtarsal joint is at it's most stable when maximally pronated. This pronation allows for the foot to more easily transfer weight across the forefoot, with the peroneals lifting the foot off the ground from lateral to medial. As the STJ moves from a supinated to a pronated state, the range of motion of the midtarsal joint increases. This increase may be exponential.

MASS PositionTheory
The MASS (Maximum Arch Subtalar Supination or Maximal Arch Subtalar Stabilization) theory was first proposed by Ed Glaser, DPM. It grew out of Dr Glaser's perception of the problems associated with the traditional STJN approach. MASS captures the foot in a corrected position without reference to STJN. The position is defined as the maximal amount of closed-chain supination achievable at midstance with the heel, first, and fifth metatarsal heads in contact with the ground. By creating a full contact orthosis that supports the MASS position, one can reduce stress on the plantar tissues of the foot. Furthermore, the MASS position provides improved mechanical advantage and function to the ligaments and muscles of the foot. It also maintains adequate supination at heel strike and toe off, full contact of the forefoot on the ground at midstance, and no limitation of first MTPJ dorsiflexion.

Physical Stress Theory
The Physical Stress Theory (PST), also known as The Tissue Stress Theory, breaks stress down into two levels: tissue stress (micro) and physical stress (macro). As motion begins bones, ligaments, muscles, and other tissues begin applying stressful forces on one another before any actual movement or work is accomplished. Every tissue has a threshold for tolerating stress beyond which they injure or become painful. This is called the Pain and Injury Threshold (PIT). PST maintains that subclinical injuries caused by the tissue and physical stresses are healed on a regular basis. But when stresses become too strong or repetitive, the injuries cannot heal fast enough and could potentially lead to permanent injury or deformity. PST attempts to prevent these injuries in one of four ways:
 * 1) Place and/or maintain the structure in "optimal functional position."
 * 2) Improve the performance of the ligaments and muscle engines that support and power the structure.
 * 3) Introduce counter forces that reduce the stress on tissues.
 * 4) Introduce forces that raise the PIT.

Subtalar Joint Axis Location and Rotational Equilibrium Theory
A Axis Localização e Equilíbrio rotacional (SALRE) Teoria Subtalar Joint POR introduzido foi Kevin Kirby, DPM. A that Uma Teoria e vez Que hum Paciente tenha atingido o Limiar de dor e Lesões, estresse Tecido PODE Ser Reduzido e mantido subclínica, exercendo Forças reativas ortopédicos pronatory e / ou supinatory Em Cima do STJ Paragrafo colocá-lo em Equilíbrio. He Eua STJN Fundição Pará Uma Maior parte. ☃☃ SALRE DETEM ORTOPEDICOS that Como Forças reactivas PODE Ser Aplicado hum QUALQUÉR involucro, contrariando ASSIM Uma patologia that apresenta e ALIVIAR Uma dor.

The Foot Centering Theory
Originated by Dennis Shavelson, DPM, the Foot Centering Theory (FCT) takes into account principles of architecture, engineering, and Newtonian Law. An arch meant to be static, such as in architecture, is most effective when symmetrical. However, a dynamic arch, such as in the foot, is most effective when asymmetrical. Some feet are off centered in the rearfoot, some in the forefoot, and some are not off centered at all. The medial arch, lateral arch, and transverse arch form an off centered vault. Due to the arches being off centered, they may require additional centering support and muscle engine training to effectively act as though centered. The FCT examination classifies feet into Functional Foot Types (FFT) which can the be examined and treated as subgroups. A centering footbed, incorporating orthotic reactive forces, brace the foot in an Optimal Functioning Position (OFP). The OFP is a position that exists for each foot, in which tissue stress in closed chain function is reduced and performance of the muscle engines and stabilizers are maximized. In order to classify a foot's FFT, one must perform two tests per rearfoot and two tests per forefoot. These tests are Supinatory End Range of Motion (SERM) and Pronatory End Range of Motion (PERM). The Foot Centering Theory is the only foot posture theory currently pending patent with the U.S. Patent Agency.

==Sagittal Plane Block Theory == Howard Dananberg, DPM, first introduced the Sagittal Plane Block Theory, which promotes the concept that the sagittal plane rockers of the foot must be evaluated and treated if their function is reduced in closed chain. It relies on gait analysis and the use of sagittal plane lifts and cutouts to apply counter force to a generic orthotic shell that is then "corrected" by repeat gait evaluation "on the fly". This theory focuses on first MTPJ functional hallux limitus and ankle equinus as causative. Sagittal Plane Block Theory has many practical over the counter applications.