<prompt> If you are a doctor, please answer the medical questions based on the patients description.About a week ago i fell and hit my knee. It did not bruise, but my knee hurts when I kneel. I looked at my knee today and noticed a bubble of sorts that hurts when I touch it. Is this pooled blood? If so, do I have to have it drained or do I just wait it out?  <response>: Hi, In your case, there are few possible causes and if there was no injury then some other chronic disorder may be present. Without more information it is not enough to determine the diagnosis. It could be a hematoma bleeding in the tissues or a swollen knee joint capsule. If its in the back of the knee then it could be a Bakers cyst. Clinical examination and perhaps fluid aspiration if theres any would help to determine the diagnosis. Either an orthopedics specialist or your primary care physician can do that. Until then, you can try to apply ice packs not directly on the skin - wrap them with a towel and perhaps use some painkillers starting with paracetamol acetaminophen and advancing to NSAID if paracetamol is not enough and theres no contraindication for NSAID. Hope I have answered your query. Let me know if I can assist you further. 