Our son had ACL surgery 3 weeks ago and started to get a rash about a week ago around the knee which is very red swollen and itchy. What to do?

?allergy to sutures. this should be seen by his surgeon.give him benadryl (diphenhydramine) for itching,keep leg elevated but see his dr.
ACL. Rash starting 2weeks after acl: consider infection, local cellulitis, irritation from tapes, glues, cleaning solutions. Check with orthopedic surgeon. Keep the area cleaned with soap & water to remove irritants.
It could be a. Dermatitis caused by the adhesive in the bandage. Contact the surgeon's office and be sure to make a note of any other symptoms, like fever, bruising, etc.