I had a lateral release on my knee 5 months ago, got cellulitis immediately after surgery and now my knee is warm to the touch. could it be infected?

Yes.: Go back to your surgeon to have it examined. It may not be, but the risk of waiting is not worth it.

Possibly: Difficult to say without an exam. Usually celulitis will resolve with oral antibiotics. The question is whether your knee warmth is due to inflamation or a low simmering infection. Certain blood tests as well as possibly drawing fluid from the knee for culture might be necessary. I would check back with your surgeon for re-evaluation.

Possible: Certainly sounds possible- let your surgeon take a look at it.