It's associated with feet which over pronate. I had two in my left foot. Temporarily controlled by steroid injections. Then I saw a good podiatrist, someone who taught at the local college of podiatry. I needed shoes engineered for stability and inserts (orthotic insoles) which had a "met pad" which kept the bones of the forefoot separated. All can be found at a very good shoe store where the staff is trained to know what you need.