Why do knee injuries (like on your skin type, not muscular) take so long to heal? like, months for a little scratch to go away? everything else heals fast/normally but my knees take at least 6 weeks for a simple nick. anything i can do to help it?

Knees: I know it. I have a wound on my knee that reminds of this since I was a child. Knees are thick skinned and the joint gets a lot of stress. There for poor blood supply and tension. More difficult for scar tissue to appropriately do its job. Vitamin A, copper and zinc along with vitamin C will support better wound healing. Also keep all knee injuries covered. Protection and warmth help too!