Hi,Dear.Thanks for the query to HCM virtual clinic.
I studied your query in all its details and understood your health concerns.
Cause and Remedy-
In my opinion the cause of the painful
lump behind knee is related to 20 yrs truck accident,which lead to arthritis of knee joint.
The lump seems to be MB (Morant Baker's)
Cyst on back of the knee joint.
USG would fix its diagnosis.
Xray knee would confirm
knee arthritis.
This lump needs consultation from ER Ortho-Surgeon.
who would treat by medicines first or by surgical removal of the MB cyst lump.
Hope this would reply your query to your satisfaction.
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Welcome for any further query in this regard to HCM.
Have a Good Day.
Dr.Savaskar M.N.