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More than the lump the pain is a concern. The swelling could be due to an soft tissue injury or due to leakage of synovial fluid. But the pain from a soft tissue (non serious) injury should not last more than few days. A fracture of the metacarpals or carpel bones has to ruled out. You will need an xray of the hand. Meanwhile DO NOT move the wrist much and do not carry weights. Keep it in neutral rested position. A OTC pain medication like Ibuprofen can be taken.
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