Anatomical diagrams illustrating the components of the plantar fascia.
Dissection of the plantar aponeurosis:
LP, lateral part; CP, central part; MP, medial part; L, length; W, width.
Five central part plantar aponeurosis bundles.
The plantar fascia is a broad structure that spans between the medial calcaneal tubercle and the proximal phalanges of the toes. Recent studies suggest that the plantar fascia is actually an aponeurosis rather than true fascia. The Dorland’s Medical Dictionary defines an aponeurosis as: (i) a white, flattened or ribbon-like tendinous expansion, serving mainly to connect a muscle with the parts that it moves, (ii) a term formerly applied to certain fasciae. Further, it defines the plantar aponeurosis as bands of fibrous connective tissue radiating toward the bases of the toes from the medial process of the tuber calcanei (posterior half of the calcaneus).
The plantar fascia is made up of predominantly longitudinally oriented collagen fibers. There are three distinct structural components: the medial component, the central component (plantar aponeurosis), and the lateral component (see diagram at right). The central component is the largest and most prominent.
In younger people the plantar fascia is also intimately related to the Achilles tendon, with a continuous fascial connection between the two from the distal aspect of the Achilles to the origin of the plantar fascia at the calcaneal tubercle. However, the continuity of this connection decreases with age to a point that in the elderly there are few, if any, connecting fibers. There are also distinct attachments of the plantar fascia and the Achilles tendon to the calcaneus so the two do not directly contact each other. Nevertheless, there is an indirect relationship whereby if the toes are dorsiflexed, the plantar fascia tightens via the windlass mechanism. If a tensile force is then generated in the Achilles tendon it will increase tensile strain in the plantar fascia. Clinically, this relationship has been used as a basis for treatment for plantar fasciitis, with stretches and night stretch splinting being applied to the gastrocnemius/soleus muscle unit.