Enthesitis, otherwise known as enthesiopathy is where supporting structures attach onto a bone.
There are loads of entheses in the body, but the ones that are most often effected in the foot are the Achilles tendon, plantar fascia,tibialis posterior, peroneus brevis and tibialis anterior.
When you have enthesitis as a result of doing too much, then supports, exercises, anti-inflammatories, activity pacing and other strategies can be very effective and can quickly settle your symptoms.
If your symptoms are seemingly without a mechanical cause (idiopathic), then a more detailed history may be needed. Sometimes these conditions are the result of other problems you might have, such as psoriasis / IBS, some types of back pain, medicines you have taken or infections you have had recently.
The enthesis is the point at which ligaments and tendons attach to bones. Enthesitis can be due to activity, but also due to certain health conditions.