Biomechanics contribute to plantar fasciitis treatment

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Biomechanics Magazine March 2007

http://www.biomech.com/showArticle.jhtml?articleID=197800665

Biomechanics contribute to plantar fasciitis treatment

Many factors go into developing a preventive protocol and proper

care for this condition

By: Josh Dubin, DC, CSCS

Plantar fasciitis is a common occupational and sport-related

repetitive strain injury. Approximately two million people in the

U.S. are treated annually for the condition.1-4 The chief initial

complaint is typically a sharp pain in the inner aspect of the heel

and arch of the foot with the first few steps in the morning or

after long periods of nonweight-bearing. After walking 10 to 12

steps, the plantar fascia usually stretches and the pain gradually

diminishes. However, symptoms may resurface as throbbing, a dull

ache, or a fatiguelike sensation in the medial arch of the foot

after prolonged periods of standing, especially on unyielding cement

surfaces.5-8

The plantar fascia is a thick, fibrous, relatively inelastic sheet

of connective tissue originating at the medial heel. It then passes

over the superficial musculature of the foot and inserts onto the

base of each toe (Figures 1A, 1B). The plantar fascia is the main

stabilizer of the medial longitudinal arch of the foot against

ground reaction forces and is instrumental in reconfiguring the foot

into a rigid platform before toe-off.4,9,10 Under normal conditions,

the plantar fascia performs this function appropriately without

incurring injury.

Some risk factors for plantar fasciitis include faulty mechanics of

the foot due to structural abnormalities, age-related degenerative

changes, excess weight, training errors, and occupations involving

prolonged standing. Those falling into this category include

teachers, construction workers, cooks, nurses, military personnel,

and athletes training for long distance running events.7,8,11-14 In

the presence of these risk factors, excessive tensile forces may

cause microtears in the plantar fascia. Repetitive trauma to the

plantar fascia exceeding the tissue's ability to recover may lead to

degenerative changes and an increased risk of injury.5,15,16

Implementing a conservative treatment and preventive protocol has

been shown to be effective in resolving or reducing the symptoms

associated with plantar fasciitis.17,18

An understanding of the anatomy and kinematics of the foot and

ankle, the static and dynamic function of the plantar fascia during

ambulation, and the contributing risk factors associated with

plantar fasciitis aid in developing a proper treatment and

preventive protocol for this condition.

Anatomy of the plantar fascia

The foot and ankle can be divided into the rearfoot, midfoot, and

forefoot. The rearfoot consists of four bones: the distal aspects of

the tibia and fibula (leg bones), the calcaneus (heel bone), and the

talus. The midfoot consists of five bones: the cuboid, the

navicular, and three cuneiforms. The forefoot consists of 19 bones:

five metatarsal bones and 14 phalanges. The plantar fascia

originates from the medial calcaneal tuberosity and divides into

medial, central, and lateral bands that attach to the superior

surface of the abductor hallucis, flexor digitorum brevis, and

abductor digiti minimi muscles, respectively. The fascia then splits

into five slips that cross the metatarsophalangeal joints and insert

onto the phalanges of the digits.1,8,19,20

The foot has a visible medial longitudinal arch (MLA) that aids in

distributing the force attributed to weight-bearing. The structure

of the foot's MLA resembles two rods: a rear rod consisting of the

calcaneus and talus, and an anterior rod consisting of the

navicular, three cuneiforms, and the first three metatarsals. These

rods are connected at their bases by the plantar fascia. When force

is applied to the apex of the MLA, the arch depresses, the two rods

separate, and tension is distributed throughout the plantar fascia

(Figures 2A, 2B).8,21 The main ligaments that aid in supporting the

MLA are the long and short plantar ligaments and the

calcaneonavicular ligament (spring ligament). During static stance,

the MLA is supported by the plantar fascia, the ligaments, and the

osseous architecture of the foot.1,8,20 During late ambulation, the

plantar fascia assumes a dynamic role in reconfiguring both the MLA

and the rearfoot in preparation for toe-off.22,23

Foot and ankle biomechanics during ambulation

Gait can be separated into the stance phase and the swing phase.

During the stance phase, the foot contacts and adapts to the ground

surface. During the swing phase, the swing leg accelerates forward

and prepares for ground contact. The stance phase consists of four

subphases: initial contact, loading response, midstance, and

terminal stance. During initial contact, the heel contacts the

ground surface. The loading response occurs immediately after

initial contact, ending when the contralateral foot lifts off of the

ground surface. Midstance starts when the contralateral foot lifts

off of the ground surface. The contralateral leg is now in swing

phase. The midstance phase ends as tension on the gastrocnemius,

soleus, and Achilles tendon (triceps surae) of the stance leg causes

the heel to lift. Terminal stance phase begins when the heel lifts

and ends when the swing leg contacts the ground.19,20,24 The plantar

fascia and extrinsic and intrinsic musculature of the foot play an

active role in guiding the foot as it transitions from initial

contact to toe-off. Efficient function of the plantar fascia and

musculature of the foot depends on the configuration of the rearfoot

and midfoot articulations during the different subphases of

gait.8,25,26

The rearfoot comprises the talocrural and the subtalar joints. The

talocrural joint (ankle mortise) consists of the articulation of the

distal aspect of the tibia and fibula with the trochlea of the

talus. It facilitates two primary movements: dorsiflexion, pulling

the toes up and back toward the tibia, and plantar flexion, pointing

the toes downward.8,19,27,28

The subtalar joint (STJ) consists of the articulation of the

undersurface of the talus with the calcaneus. Movement of the

subtalar joint is pivotal in transforming the foot from a rigid

lever during initial ground contact to a mobile shock absorber

during loading response and early midstance, and back into a rigid

lever as the foot prepares for toe-off. The two primary movements

that occur at the STJ are pronation and supination. Pronation of the

STJ normally occurs during loading response and into early

midstance. In STJ pronation, the calcaneus turns outward (everts);

the talus drops downward distally and adducts toward the midline;

and the talocrural joint dorsiflexes. During initial contact, the

STJ is normally supinated. It pronates from loading response to

early midstance and then resupinates later in midstance and into

terminal stance. In STJ supination, the calcaneus turns inward

(inverts); the talus moves upward proximally and abducts away from

the midline; and the talocrural joint plantar-flexes. Freedom of

movement in the midfoot depends on the position of the STJ.8,19,20

The two main articulations of the midfoot are the talonavicular

joint and the calcaneocuboid joint. The midfoot revolves around two

joint axes: the longitudinal midtarsal joint angle (LMJA) and the

oblique midtarsal joint angle (OMJA). Movement of the midfoot around

the LMJA consists of inversion (supination around the LMJA) or

eversion (pronation around the LMJA). Movement of the midfoot around

the OMJA consists of dorsiflexion and abduction (pronation around

the OMJA), and plantar flexion and adduction (supination around the

OMJA).

STJ pronation during loading response and into early midstance

causes the talonavicular joint to diverge and move distally to the

calcaneocuboid joint. This reconfiguration unlocks the midfoot,

allowing it to pronate around the OMJA. Pronation of the midfoot

around the OMJA will stretch the plantar fascia slightly as the MLA

is depressed, transforming the foot from a rigid lever into a mobile

adaptor that is better equipped to absorb ground reaction forces.

Shortly after early midstance, the STJ starts to resupinate and

should resupinate back to neutral before terminal stance. STJ

resupination causes the talonavicular joint to move proximally to

the calcaneonavicular joint, superimposing these joints and limiting

midfoot and forefoot ranges of motion. STJ resupination during

midstance locks the lateral column of the foot, including the

calcaneocuboid joint, allowing the muscles and fascia of the leg and

foot to function more efficiently in guiding the foot into toe-

off.8,19,20

The peroneus longus and the plantar fascia are actively involved in

preparing the foot for toe-off. The tendon of the peroneus longus

muscle passes over the outer, plantar aspect of the calcaneocuboid

joint and attaches to the undersurface of the base of the first

metatarsal. During late midstance, the calcaneocuboid joint

functions as a pulley for the tendon of the peroneus longus. This

allows the peroneus longus tendon to stabilize the base of the first

metatarsal and aid in transferring body weight medially over digits

one through three. The stability of the calcaneocuboid joint pulley

system depends on the STJ resupinating during midstance. Later,

during terminal stance, the metatarsophalangeal joint of the first

digit should dorsiflex to approximately 65 degrees , causing the

distal aspect of the plantar fascia to wrap around the

metatarsophalangeal joint. These coordinated movements that occur

during terminal stance have been termed a windlass mechanism.8,19,20

During this motion, tension on the distal aspect of the plantar

fascia is transmitted to its proximal attachment on the medial

aspect of the heel, causing the calcaneus to invert and the medial

arch to rise as the forefoot pulls back toward the

rearfoot.1,21,23,25

Studies have demonstrated that when 33% or more of the plantar

fascia is surgically released, the medial arch decreases in height

and the plantar fascia loses its ability to invert the

calcaneus.21,23,29 During late stance the dynamic action of the

peroneus longus and the plantar fascia prepares the foot for an

energy-efficient, high-gear toe-off that occurs in a horizontal line

over the metatarsophalangeal joints of digits one through three.

Inability of the STJ to resupinate to neutral before heel lift

places an increased load on the plantar fascia and peroneus longus

as they attempt to stabilize the foot for toe-off. This may

predispose the plantar fascia to injury and also result in a less

efficient, low-gear toe-off that occurs in an oblique line over the

metatarsophalangeal joints of digits three, four, and five.8

Other muscles that help stabilize the MLA and resupinate the foot

include the abductor hallucis, flexor digitorum brevis, flexor

digitorum longus, flexor hallucis longus, and tibialis posterior.

The abductor hallucis and flexor digitorum brevis aid in restoring

the MLA to its arched position and stabilizing the foot before toe-

off. The flexor digitorum longus, flexor hallucis longus, and the

tibialis posterior have tendinous attachment sites near the MLA. The

former two muscles are active in resisting pronation from midstance

to toe-off, and the tibialis posterior decelerates pronation from

loading response to early midstance.8,19,20

Under normal circumstances, the plantar fascia, plantar ligaments,

osseous architecture, and extrinsic and intrinsic muscles of the

foot and leg are able to absorb ground reaction forces without

incurring injury. However, structural abnormalities may lead to

faulty biomechanics of the rearfoot and midfoot. These abnormalities

may cause excessive and rapid pronation of the STJ during loading

response and into early midstance, or ill-timed pronation that

continues into terminal stance. This may lead to an increased strain

on the plantar fascia and other supporting structures of the foot,

predisposing a person to developing plantar fasciitis. Structural

abnormalities associated with excess, prolonged, or ill-timed

pronation may include ankle equinus, rearfoot varus, forefoot varus,

pes plano valgus, and pes cavus (see table, page 40).1,2,21,28,30

Other associated risk factors

Training errors contribute to most overuse injuries associated with

running. Properly progressed training programs allow the supporting

structures of the lower extremities to adapt to increased stresses.

Inappropriately increasing the intensity, duration, and frequency of

training runs, as well as incorporating hills on the training routes

too soon, may overload the supporting structures of the lower

extremity, eventually leading to injury.11,30,31

Excess weight, age-related degenerative changes, and occupations

requiring prolonged standing or ambulation contribute to the risk of

plantar fasciitis.1,3,5,11,30,32 Ground reaction forces acting on

the plantar fascia and other supporting structures of the foot can

reach 1.2 times body weight with walking, and 2.5 to three times

body weight with running.1,11,25 An injured recreational runner may

gain weight if he or she fails to cross train and/or follow proper

nutritional guidelines during periods of inactivity. Deconditioned,

heavier runners may be predisposed to injury if they progress their

training program inappropriately. Obese, sedentary individuals are

also predisposed to plantar fasciitis. Studies have indicated an

association between plantar fasciitis and those whose body mass

index is 30 kg/m2 or higher.28,30

Based on clinical experience, occupations that require prolonged

standing on unyielding surfaces predispose the plantar fascia and

other supporting structures of the MLA to repetitive tensile ground

reaction forces.13,14,32 Age-related degenerative changes to the

plantar fascia and to the fat pad of the heel may predispose older

people to injury by reducing the shock absorption capabilities of

the foot and the ability of the plantar fascia to dissipate tensile

forces.10,11

C. Dubin, DC, CSCS, is the owner of Dubin Chiropractic in

Quincy, MA. He has been a member of the Team USA Triathlon/Duathlon

International Triathlon Union medical staff since 1996.

This is part I of a two-part article. Next month, part II will look

at various treatment options for plantar fasciitis.

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