June 1995
BIOMECHANICAL FUNCTIONS OF THE "INTACT" PLANTAR FASCIA
If I were an inflamed plantar fascia, I would be afraid to enter many podiatrists' offices these days.
Why?
Because there are so many podiatrists cutting on the plantar fascia to relieve plantar fasciitis that it is scary.
Don't these doctors realize that there are other ways of treating plantar fasciitis that don't permanently alter the structure and function of the foot?
The plantar fascia is very important to proper foot function because it is the retaining cable of the plantar longitudinal arch of the foot.
From its origin on the calcaneal tubercle to its insertions on the proximal phalanges of the digits, it has very definite and important biomechanical functions.
In order for the plantar fascia to serve its important functions in the human foot, it must, however, remain intact.
To make it very clear that major permanent biomechanical changes occur in the foot with surgical transection of the plantar fascia, I have developed a list of seven of the most important biomechanical functions of the plantar fascia.
I suggest that before a plantar fasciotomy is performed these vital functions of the plantar fascia be reviewed to make sure the potential harm of the fasciotomy is not greater than the potential benefit.
1.
The plantar fascia serves to hold the medial longitudinal arch in a higher arched position during standing and walking.
Even though the plantar fascia is not a muscle, it does have the ability to prevent medial longitudinal arch collapse during weightbearing activities.
Because of its attachments on the calcaneal tubercle and the bases of the proximal phalanges of the digits it can directly limit elongation of the medial longitudinal arch and therefore help prevent arch collapse.
2.
The plantar fascia assists in resupination of the subtalar joint during the propulsive phase of walking gait.
Since the medial band of the plantar fascia attaches to the sesamoids and then onto the base of the proximal phalanx of the hallux, dorsiflexion of the hallux will produce an arch raising effect (better known as the Windlass Effect of Hicks).
During propulsion, the hallux is dorsiflexed at the first metatarsophalangeal joint (MPJ) which causes a relative plantarflexion of the first ray which then, in turn, produces increases supination of the subtalar joint (STJ).
A foot without an intact plantar fascia will have limited resupination during propulsion and will have a less propulsive gait pattern.
3.
The plantar fascia assists the deep posterior compartment muscles by helping to limit STJ pronation during standing and walking activities.
An intact plantar fascia acts to cause a supination force on the STJ during weightbearing activities by limiting the collapse of the medial longitudinal arch.
The plantar fascia is under the greatest tension during the latter stages of midstance once the center of mass of the body has moved anterior to the ankle joint axis.
When the plantar fascia is intact, the posterior tibial, flexor digitorum longus and flexor hallucis longus muscles do not have to contract as vigorously to decelerate pronation or accelerate supination of the STJ.
4.
The plantar fascia assists the plantar intrinsic muscles.
The medial band of the plantar fascia specifically assists the abductor hallucis and flexor hallucis brevis muscles in limiting medial longitudinal arch collapse.
The lateral bands of the plantar fascia assist the more laterally located muscles of the plantar arch in limiting lateral longitudinal arch collapse.
Without an intact plantar fascia the plantar intrinsic muscles must contract much more vigorously to maintain arch height.
5.
The plantar fascia prevents excessive interosseous compression forces on the dorsal joint surfaces of the bones of the medial and lateral longitudinal arch.
By acting as a retaining ligament for the longitudinal arches of the foot, the plantar fascia directly decreases interosseous compression forces on the dorsal joint surfaces of the talo-navicular joint, navicular-cuneiform joints, cuneiform-metatarsal joints, calcaneo-cuboid joint and cuboid-metatarsal joints.
Without an intact plantar fascia the increased dorsal interosseous compression forces which result can cause painful dorsal midfoot arthralgia.
6.
The plantar fascia helps maintain purchase of the digits during standing and prevents "floating toes".
The plantar fascia inserts onto the bases of the proximal phalanx of the digits and causes a plantarflexion moment across the MPJs when the foot is loaded by ground reaction forces.
Without an intact plantar fascia some of the plantarflexion moment on the MPJs is lost during weightbearing activities and the digits will not purchase the ground as well as before.
7.
Because of its inherent elasticity, the plantar fascia acts to store energy within the arch structure of the foot during dynamic loading activities.
The plantar fascia is very important in dynamic activities such as running and jumping since it is an elastic structure.
The plantar fascia acts like a spring along the plantar arch of the foot to first absorb energy during arch collapse and then return that energy during propulsion when the arch is raising.
The Achilles tendon and plantar fascia work synergistically to add extra "spring" to running and jumping activities.
Plantar fasciotomies cause a loss in this "elastic energy" in the foot and should be considered only as a last resort for treatment in competitive or serious recreational athletes.
[Reprinted with permission from: Kirby KA.:
Foot and Lower Extremity Biomechanics:
A Ten Year Collecction of Precision Intricast Newsletters. Precision Intricast, Inc., Payson, AZ, 1997, pp. 45-46.]
Click to expand...