Hello and welcome to HCM,
According to the history provided by you it seems that there is some movable lesion in your knee joint which moves in different directions as you move your knee.
This lesion is most probably due to a cyst
of the knee joint would help to know the character of the lesion- whether it is solid or cystic.
Cysts are common around the joints and they are commonly seen after inflammatory conditions e.g. osteochondritis
in your case.
The cysts can be removed arthroscopically.
Consult your orthopedician for clinical examination, investigations and management.
Thanks and take care
Dr Shailja P Wahal