Have sinivitis pigmentosa behind knee, have painful muscle pull in calf, swollen ankle. Worried

My husband (72) suffered with sinivitis pigmentosa behind his left knee and had several surgeries for it over a number of years, but it always came back. About 16 years ago he had a procedure done at Baylor University Hospital, Houston that involved nuclear treatments and he has been asymptomatic since. A couple of weeks ago he pulled a muscle in his calf - it was painful, and his ankle has been swelling up since. His calf hurts. A visit to our Family Practice Physician determined that he probably strained his calf muscle and an ultrasound showed no blood clot. He is very worried about the sinivitis recurring and asked me to see what I could find out, What are the chances, or is he overly worried?