Foot Biomechanical Theories Explained

The treatment of foot pathologies requires an understanding of complex lower limb biomechanics theories. This involves a multitude of areas of activity used in the prescription of a host of medical devices for different conditions of the foot.

The Subtalar Joint Theory introduced the concept of neutral position of the subtalar joint in classifying normal and pathological foot structure. On the basis of this theory, it became clear that there was an important biomechanical relationship between the subtalar joint and the midtarsal joint, which needed to be considered as the origin of mechanical foot dysfunction.

This allowed clinicians worldwide to treat the root cause of the problem, and not just the symptoms, working off the notion that changing the plantar contour of the foot using orthotics, would change the position of the subtalar joint and subsequently, the motion of the midtarsal joint.

Perhaps, one of the greatest accomplishments of this theory, was the creation of a unified reference system for normal foot definition in the form of a set of 8 criteria of normalcy.

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Any deviation from these criteria, signalled the presence of a structural deformity or muscle imbalance, forcing the body to resort to compensatory movements.

However, the biggest criticisms of Root’s paradigm related to the intra and inter-observer reliability of static biomechanical examination; the applicability of criteria or normalcy to the population; the validity of using such a method for determining the neutral position by challenging the supination and pronation ratio of 2:1; and the dynamic behaviour of the subtalar joint.

The Sagittal Plane Facilitation Theory focused more on the role of a functional hallux limitus in functional foot pathomechanics. This was based on the concept that in order to achieve propulsion, the hallux cannot fully perform the dorsiflexion movement required.

A plantarflexion movement of the first metatarsal is necessary to achieve a dorsiflexion movement of the hallux greater than 25-30 degrees.

This functional incapability hinders the performance of tasks specific to propulsion during the gait cycle, and is the reason for the occurrence of compensatory movements associated with common foot conditions.

This theory holds that any blockages in the movement of the sagittal plane causes dysfunctionality in intrinsic joints of the foot and lower limbs leading to compensatory movements; hence, the main goal of treatment would be to facilitate the plantarflexion and eversion movement of the first metatarsal as well as the hallux dorsiflexion movement.

The Tissue Stress Theory breaks stress down into two levels: tissue stress (micro) and physical stress (macro), focusing more on the kinetic assessment of gait. According to this theory, maintaining deformities in anatomical structures within the limits of elasticity will make the patient experience a tolerable degree of internal stress in the tissues.

An increase in the load or changing the level of activity will cause the tissues to shift from the elastic to plastic deformation, leading to microtrauma and symptoms associated with overuse.

The 4-stage protocol recommended involves identifying anatomical areas where pain is prevalent, applying controlled stress on the identified areas, to determine whether the pathology is mechanical and prescribing conservative forms of treatment to reduce stress in tissues.

The MASS (Maximum Arch Supination Stabilisation) Position Theory worked on the limitations of the Subtalar Joint Theory, focusing more on capturing the foot in a corrected position with no reference to the subtalar joint.

This position is defined as the maximal amount of closed-chain supination achievable at midstance with the heel, first and fifth metatarsal heads all in contact with the ground. Based on this, a full-contact orthotic should be created to support this position and to reduce the stress on the plantar tissues of the foot.

The many mechanical advantages of this theory involve the improved functionality of the ligaments and muscles of the foot, with no limitation of the first metatarsophalangeal joint.

The Integrated Multi-Axial Posture Theory™ finds its roots in this theory, focusing on establishing a foot posture which results in optimum neuromuscular efficiency, reducing the stress placed on the entire kinetic chain so that tasks can be performed with the most amount of efficiency.

Postural stability is crucial to boost optimal articulation alignment which, in turn, facilitates optimal arthrokinematics of the foot and ankle.

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References:

1. Petcu Daniel, Anca Colda (2012) Foot Functioning Paradigms. Proc. Rom. Acad.: January 20, 2012, Series B, Vol. 14, No. 3, pp. 212-217.

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