Thanks for your query.
Without a clinical evaluation it would be difficult to determine the cause of the knot. Possibilities that may need to be considered include lipomas
, cysts, growths from underlying connective tissue
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.