Hello, Marc. I am one of the swan veterniarians for The Regal Swan Foundation. I am not sure what you mean by the term "blown out" knee, and I am not certain where the lesion is on the feet of the swan you have pictured. I presume the swan is limping? Sheila Bolin had given some advice about the possibility of a slipped tendon. A slipped tendon occurs in very young waterfowl, typically under 3 or 4 weeks of age. The swan in your picture does not have a slipped tendon, but needs to be examined by a veterinarian. X-Rays may be necessary, especially if the problem involves the bone.

Good luck with your swan. -- Christopher W. Brown, DVM