Cause and origin

Behind the synonym "plantar heel spur" lies a wide variety of reactions to pain in the heel. A bony protrusion often develops at the base of the tendons – identifiable as a spur in an X-ray – but the majority of pain is caused by excessive pull on the muscles and tendons attached to the calcaneus (heel bone).

Virtually all short foot muscles originate at the heel. The short toe muscles sit at the frontal side of the heel. If the toes are then forced to tense up, the pull on the calcaneus increases. Once again, special attention should be paid to the big toe.
The abductor hallucis sits exactly where the majority of heel spur pain occurs. If the big toe is then forced out of its natural position (hallux valgus), the pull of this muscle increases considerably. The periosteum (membrane covering the outside of the bone) at the heel is irritated to such an extent in this area that it is difficult to walk. However, the flexor digitorum brevis can also cause pain if the toes are dug in over a long period of time due to pain in the forefoot.

Depressing the longitudinal arch, and therefore extending the foot, has the same effect. 
This phenomenon occurs if unusually high weight is affecting the foot. Pregnancy can lead to flattening and extension of the foot by one shoe size.
The majority of people experience this flattening around the age of 50 due to age. A normal foot extends up to three sizes, a foot with a high arch up to four sizes, throughout the rest of their life.

The change in length happens very quickly, usually following extraordinary strain. The collapse considerably increases muscle and tendon tension at the heel, potentially causing sudden heel pain.

However, if the surface that comes into contact with the ground when stepping is squint, this can also cause plantar and dorsal heel pain (see achillodynia). This squintness is formed by a shoe with a soft heel or a heel that has been worn down at the side. Even one to two millimetres are enough to have a long-lasting effect. If the squintness is even greater, the effects are exponentiated.
Another reason for suffering periosteum irritation at the heel is wearing sandals or clogs with a deep footbed. For the majority of wearers, the curvature at the heel is too narrow, causing lateral rubbing on the heel bone with every step. The external indication of this maldistribution of stress is a wound around the heel. Natural walking causes the outside of the heel to be put under considerably more strain, generally causing lateral heel pain.