If you have pain under the big toe joint, it could be an injury called sesamoiditis. Sesamoid bones are like a pair of tiny little kneecaps under the big toe joint. They are about the size of kidney beans. If irritated enough, sesamoid can develop stress fractures.

Any inflammation of the sesamoid bones is called sesamoiditis. 

But pain in the sesamoid area can also result from inflammation of the tendon sheath that goes around the flexor tendon. The flexor tendon sheath is just a tube around the tendon that actually helps the tendon glide as your big toe moves up and down. 

The flexor tendon sheath is very close to the sesamoids.  Sometimes it is hard for a runner to tell the two conditions apart.

There's a big difference between the two conditions and a big difference between the way that you would treat them.

What's the difference between flexor hallucis longus tenosynovitis and sesamoiditis? 

Well, that's what we're talking about today on the Doc On The Run Podcast.