Is it rare to have reflex sympathetic dystrophy in the knee?

Yes: Rsd or chronic regional pain syndrome is usually seen in the upper or lower extremities and usually involves a wider area than the knee itself. For instance, we may see it involving the calf, ankle and foot or hand wrist and forearm. I have heard of this diagnosis being made in a single joint like the knee but I have never seen it myself.

Yes: Rsd affects larger areas such as the ankle and foot or an area from the knee down to the foot. I have even seen the entire leg affected. Upper extremities can also be affected. An isolated area such as the knee would be very uncommon for rsd.

Not at all: RSD commonly affects extremities, particularly in locations susceptible to trauma. The knee may be involved secondary to a blunt trauma or sports injury, and after surgery such as arthroscopy or joint replacement.