<s>[INST] I have a hard almost boney lump on the posterior side of my ankle.\On top of a tendon that goes around the back of the ankle bone coming up from the arch. had an injury but it was not debilitating and I kept playing basketball... It almost went away when I was on vacation last summer after three weeks but when I started playing basketball and volleyball aainnit came back got larger and harder... Not rest does not seem to reduce it s size. I have little pain and can still un and jump but it looks like I have two ankle bones on the side. Any idea what it is? Or what I should do? [/INST] this sounds like you have a ganglion. There are many small bags filled with gelatin like fluid around joints to reduce friction. these enlarge on activity and may subside a little when long periods of rest are given to the joint. If this is the case it is not something u should worry much but it increases in size or causes pain during your activites it can be removed with a small surgical procedure. but again this may reoccur in some cases. you should get it examined by a local surgeon or a bone specialist to confirm because examination might reveal something that may need to be investigated but otherwise does not sound like something u should worry. </s>