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1.There can be a scar tissue formation after healing wound - possibly you are feeling it as lump, as there is no pain as you mentioned.
2.The next possible cause could be
ganglion formation from the joint space.
3.These ganglions are generally from the joint space
cartilage, tendon and so on, which does not need any treatment but followup.
4.Apply anti inflammatory cream if you feel any soreness or oedematous.
5.If not responding - let it get examined by your GP, then further action can be taken according to the examination.
Good luck.
Hope i have answered your query,
any thing to ask ? do not hesitate to ask.
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