My little horse developed a strange lump at the back of her pastern, between her ergot and her heel bulbs as shown in the photo below. It first appeared last summer. It has never made her lame, and she has had her legs ultra sound scanned by my vet, who also ruled out any damage to her tendon sheath.The puzzling thing is whilst the lump appears overnight, although it no longer puffs up her fetlock or the any other sections of this pastern, it does disappear when she is exercised or turned out. It has puzzled every vet and farrier I have questioned about it and I just wondered if anyone out there has had anything similar happen to their horse. It is a tiny hard lump, feels almost like a ridge as if someone has inserted a very small rubber under the skin.