Hi Sal,

Interesting case. The most common lateral (outside) knee pain in runners is Iliotibial band friction syndrome which is pretty much what your friend was talking about. Not sure if its the cause here given that you say the pain can radiate down half your lower leg as well but could well be the reason. Did you do much work on your ITB's while resting or did you just not run?

To get a better idea of whats going on you'd need to answer the following:
Was the pain something that came on suddenly or did it build gradually over a period of time? What type of pain is it (i.e. Is it a sharp shooting pain or more of a generalised ache, etc)? Does the pain feel deep inside the knee or to the surface (ie just under the skin). Have you any back pain or stiffness at the moment? Do you only get pain with running or do other loading exercises cause pain (jumping jacks, hops on spot).

Answer those and it'll help get a better picture.