In what way is my knee injured?

It sounds like a fracture or at least it was. If this was the case, the bone could have healed the wrong way causing your pain now. Go to an orthopedic surgeon. They will definitely want to do xrays and feel your knee. If they cannot find the cause of your pain after xrays and an MRI, they might consider doing an arthroscope to look around and see whats wrong.