What Causes Lesions On Elbow And Upper Leg Post Knee Replacement Surgery?

I had a knee replacement about a year ago. Following that, I experienced a couple of previously unexperienced boil like lesions at a couple of places on my skin (one on elbow and one on upper leg) that soon ran there course and disappeared after about 2 weeks. Then about 6 months after the surgery I contracted cellulitous in my opposite leg which was treated with antibiotics and cured. Since that time, the cellulitous infected leg has occasionally experienced hotness under the skin. Anything to be concerned about?