Hello,
Welcome to ehealthforum and thanks for writing
Knot like structure on the rib could be an enlarged lymph node often caused by an infection, allergic reactions, metabolic diseases or rarely cancer.If it is firm,tender and warm then could signify infectious cause.
Any cancerous knot/swelling is usually nontender,firm and matted in consistency and keeps on increasing over time.It is difficult to commnet without a proper examination.
FNAB (fine needle aspiration biopsy) of the lymph nodes and swollen glands is the best test. FNAB is aspiration of the material of the glands which is done by a fine gauge needle and a syringe. This will confirm the diagnosis.
Consider visiting a Surgeon for evaluation and if required get a Biopsy done for confirmation of disgnosis.
Take care!