Hard lump on hind leg half way between hock and fetlock??

[edwarf]

A small lump (about the size of a large pea) has appeared on the very back of my horse's hind lower leg (below the hock). After looking at the diagram below it, the lump in sitting on the superficial digital flexor tendon, and it points out toward the back.

http://2.bp.blogspot.com/_IcMoWTgbiZA/Swoh9fUMb_I/AAAAAAAAAFc/LuBus1vlFRc/s400/HindlegTendons.jpg

I pick his feet out daily and suddenly noticed it when running my hand down the back of his leg a couple of weeks ago. It seems to be causing him no pain at all, and he is completely sound. It is a very hard lump, which feels like bone. He's not had any accidents or old injuries there... unless he caught himself out in the field. He is totally healthy. But he is not in hard work at the moment.

What could this be? Any advice would be much appreciated!! thanks

 

[SS.89]

My old pony used to have something similar & it turned out to be a windgall which had gone hard.
My current ex racer is covered in lumps & bumps from his racing days and they are just old splints which cause him no lameness or pain

 

[Tnavas]

Does he wear boots or bandages when being worked? Sometimes if too tight lumps like this appear.

Windgalls are low down around and slightly above the fetlock joint.