Question about acceptance

For years, I have struggled with a chronic knee injury and chronic knee pain. I am an athlete and it is definitely not something I want in my life. I have realized that my fighting against it, refusal to accept it, is magnifying the problem and my pain. So I am trying to work on acceptance.

My concern is that if I accept the fact that my knees hurt, it leads to the feelings of sadness and disappointment. And if I allow those to stay, it turns into despair. Despair doesn’t feel like a productive emotion, or a place where I want to spend much time.

Instead I want to accept that there will be times that my knee is more painful than others, and maybe grieve the situation that I have a knee that is injured, when in my heart I would love to be an athlete without physical limitations.

How do I accept something without indulging in unproductive emotions like despair?