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The Foot Complex

Functions of the Foot
Joint Structure of the Foot
Kinematics of the Foot
Muscles at the Foot
Foot Stability
Mechanism of Injury at the Foot

Objectives： After studying this topic, the students will be able to

1. to identify the structure of the foot, including joint type, articular shape, and the surrounding tissues
2. to describe joint motions occurring at the foot, including physiological and accessory movements, muscle actions, and factors checking these motions
3. to understand the stability mechanism of the foot and the possible mechanisms of injury
4. to distinguish triplanar joint motions from single-plane motions
5. to understand the interrelated motions among foot joints during gait cycle

1. Neumann DA (2002).  Ankle and foot.  In Neumann DA: Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. Philadelphia: Mosby.  Chapter 14, pp. 477-521.
2. Smith LK, Weiss EL, Don Lehmkuhl L (1996). Brunnstrom's Clinical Kinesiology, 5th ed.  Philadelphia, F.A. Davis.  Chapter 10, pp. 332-362.
3. Sammaco GJ & Hockenbury RT (2001).  Biomechanics of the ankle and foot.  In Nordin M & Frankel VH: Basic Biomechanics of the Musculoskeletal System.  Philadelphia: Lippincott Williams & Wilkins. Chapter 9, pp.222-255.

Functions of the Foot Complex

Differences between human beings and animals

plantigrade planta = sole gradi = walk widening of the pelvis erect spine delicate hand functions

Contact areas at quiet stance vs. arches

3 contact areas at quiet stance heel first metatarsal head fifth metatarsal head 3 arches medial longitudinal arch transverse arch lateral longitudinal arch

Functions of the foot

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Joint Structure of the Foot

Joints at the Foot

subtalar joint sustentaculum tali： the process which supports the talus midtarsal joint talonavicular joint calcaneosuboid joint
5 rays first ray： 1st metatarsal + 1st cuneiform as a functional unit second ray： 2nd metatarsal + 2nd cuneiform as a functional unit third ray： 3rd metatarsal + 3rd cuneiform as a functional unit fourth ray： 4th metatarsal fifth ray： 5th metatarsal 5 metatarsophalangeal (MP) joints 9 interphalangeal joints interphalangeal (IP) joint at the big toe porximal interphalangeal (PIP) joints distal interphalangeal (DIP) joints

Subtalar joint

proximal component： inferior aspect of the talus convex anterior and medial facets concave posterior facet distal component： superior aspect of the calcaneus concave anterior and medial facets convex posterior facet joint type： pivot joint motions： triplanar motions pronation： 8-10º supination： 16-20º DOF = 1 closed-packed position： full foot supination
subtalar neutral position the position where the subtalar joint is neither pronation nor supination the position where the bisecting line of the calcaneus is perpendicular to the ground the bisecting line of the tibia is perpendicular to the ground the plantar surface of the metatarsal heads are parallel to the ground

Midtarsal joint

First Rays

Medial Longitudinal Arch

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Kinematics of the Foot

Subtalar pronation and supination

joint involved： subtalar joint plane of motion： triplane axis of rotation triplane in origin wide variety more frontal plane motions (inversion/ eversion) if the axis is more horizontal more transverse plane motions (abduciton/ adduction) if the axis is more vertical osteokinematic movements range of motion (ROM) pronation： 8-10º supination： 16-20º triplanar motions： Since the axis of the subtalar joint is not just in any cardinal plane, the motions occurring at the subtalar joint present a triplanar motion pattern.
open kinematic chain motions pronation： dorsiflexion, abduction, and eversion of the calcaneus supination： plantarflexion, adduction, and inversion of the calcaneus closed kinematic chain motions pronation： plantarflexion and adduction of the talus, eversion of the calcaneus, and internal rotation of the tibia supination： dorsiflexion and abduction of the talus, inversion of the calcaneus, and external rotation of the tibia examples： deep squatting or stance phase of the gait cycle functional range： at least 4-6º of foot pronation and 4-6º of foot supination is necessary for normal gait
arthrokinematic movements medial and inferior glide of the talus on the calcaneus with foot pronation lateral and superior glide of the talus on the calcaneus with foot supination the height of the talar head is changed from supination to pronation during closed kinematic chain motions, resulting in the shock from the ground absorbed
factors limiting STJ pronation and supination bony structure interosseus ligament
changes in the subtalar joint during the stance phase of walking motion： 1/4 pronation + 3/4 supination position： 2/3 pronated + 1/3 supinated

Midtarsal pronation and supination

joint involved： midtarsal joint plane of motion： triplane axis of rotation triplane in origin two axes longitudinal axis： angles 15° from the transverse plane and 9° from the sagittal plane oblique axis： angles 52° from the transverse plane and 57° from the sagittal plane The subtalar joint position affects the alignment of the axes of the midtarsal joint, resulting in changes in range of mitarsal motions

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Muscles Around the Foot

prime mover：

peroneus longus： eversion + plantarflexion

peroneus brevis： pure eversion

During gait cycle, pronation of the foot occurs at foot flat and midstance.
         

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Foot Stability

Medial longitudinal arch

bony configuration： most important bony congruity of tarsal and metatarsal bones： The arch is a curved beam consisting of interconnecting joints and supporting plantar ligaments metatarsal break 50-70° anterior to the frontal plane increase supination at propulsive phase important in shoe fit if the metatarsal break is not correct
tension of ligaments or other connective tissues plantar fascia from medial tuberosity of calcaneus to base of proximal phalanges windlass mechanism (Hicks, 1954) toe extension ® wind up plantar fascia ® shortening of distance between heel and metatarsal head ®elevation of the medial arch a decrease in arch height of 4 mm after plantar fasciotomy long plantar ligament short plantar ligament spring ligament (calcaneonavicular ligament)： to support the talar head contraction of muscles： not found at quiet stance for a neutral foot tibialis posterior：  note its location of the insertion intrinsic muscles：  hypertrophy noted in the pronated foot

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Mechanism of Injury at the Foot

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