The foot, with its many bones, is a complicated part of the body and number of things can cause ankle pain includilng inflammation of one of the three tendons in the ankle (tendinitis), arthritis, a tear in one of the ligaments or an ankle strain. These are usually accompanied by swelling and redness, however.
You might want to try ice/heat and elevation along with anti-inflammatories and see if they help. If you pain does not diminish, though, you should see a doctor.
You might want to try the Check a Symptom program on HealthCentral to investigate Foot and ankle pain more.
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