I Had UGS Followed by Regular Sclerotherapy and Now I Have a Large (Hand Sized) Reddened Area onKnee? (photo)

The pictures look like matting but since you have persistence of the problem and since you had a post sclerotherapy complication, I would recommend a full venous evaluation with a venous reflux exam.  I would also look for underlying reticular or feeding open vessels.  You should see a vein specialist.

This is phlebitis after sclerotherapy and is a classic presentation after injecting large superficial veins that are very close to the skin. The natural history is that there will be painful and the redness will subside but there will be some hyperpigmentation that may be permanent. I recommend something called Phlebitis PAK and also ibuprofen and a creme to minimize the hyperpigmentation and this is what I use for my patients, whenter phlebitis follows sclerotherapy or occurs spontaneoulsy (without sclerotherapy). Phlebitis PAK and a creme called VenoLucent.

The findings in the photo are typical for matting. Matting is the growth of very small red veins after a cluster of varicose veins or larger veins are treated. If the matting doesn't go away, it can be effectively treated with a vascular called pulsed dye laser . It is likely to resolve with 1-3 treatments.