Hi, thanks for writing to HCM.
As the swelling is hard to feel, it should be arising from the underlying bone.
If the swelling is painful, with local warmth over that area along with
fever, then it could be inflammatory in origin.
Painless bony swellings most propably will be bone tumours (don't get scared by this fact). Bone tumours can be Benign (relatively harmless) or Malignant (harmful cancers).
Benign bone tumours are usually slow growing in nature whereas malignant tumours are fast growing.
Clavicle is not the generally favoured site for malignant bone tumours ( hope this statement will bring down your
anxiety). So I personally feel that it could be a benign lesion.
You need to observe the swelling constantly. If the mass is growing fast or if there is any change in its consistency (feel), you need to consult an orthosurgeon immediately.
Any expanding bony lesion needs a detailed evaluation to know its histological nature.
Hope this information is helpful. Good day