Hello, Thanks for writing to us Without a clinical evaluation it would be difficult to determine the cause of the lump. Possibilities that may need to be considered include enlarged bursa, baker s cysts, growths from underlying connective tissue etc. Numbness of skin is worrisome. I would suggest getting this evaluated by an orthopedician for an accurate diagnosis and appropriate management. You may get the X-ray of the area affected and FNAC (fine needle aspiration cytology) of lump under his/her guidance. I do hope that you have found something helpful and I will be glad to answer any further query.