I did a search and a long term problem with getting/maintaining an erection after KNEE surgery and epidural does not sound to be related. However, that he is having issues with the knee still, that does. The sensation of numbness would indicate some sort of nerve involvement unless it is related also to the swelling. To be honest, seems like a long time to have these issues post surgery. Has he been back to the surgeon? He needs to go and talk about the outcome of this surgery and if he is on track to full recovery. At that time, he should mention impotence. A lot of erection is mindset and psychological and if you can't feel your leg, still uncomfortable, etc. it may impact that. Talk to the doctor for root solutions . Go gentle on him. Still be intimate but in different ways. And then you can discuss a remedy with the doctor. It should sort out over time.