There’s no healing advice just for the knee, so the general rules for healing apply here too — with one feature that does belong to this spot. The wound sits across a joint, and a joint is not something you can put down for six weeks.
The benchmark first. A wound is called non-healing if it has not started to heal in 2 weeks or has not completely healed in 6 weeks. That is the measure to apply before anything else.
On movement, be careful not to assume too much. Obesity, which slows healing, can also put tension on stitches, which can make them break open. Bending a joint is a separate question, and this article won’t claim it does the same. What is certain, and is a reason to contact your provider right away, is the outcome: a wound that has come open or the stitches or staples have come out too soon. Whatever caused it, that is a reason to make contact rather than to watch.
If the wound is a surgical one that was left open on purpose, slow is the plan, not a failure. If your surgeon does not close your wound again with sutures, you will need to care for it at home, since it may take time to heal. The wound will heal from the inside to the outside. A dressing helps absorb drainage and keeps the skin from closing before the wound underneath fills in. Knowing whether yours was closed or left open changes what counts as too slow.
Two rules matter for a knee: do not wear tight clothing that rubs against the incision while it is healing, and do not pull at your stitches or try to remove them on your own.
Then the general reasons, which apply here as anywhere: infection, diabetes, poor blood flow, obesity, age, heavy alcohol use, stress, certain medicines — corticosteroids, NSAIDs and some chemotherapy medicines — and smoking, plus nerve damage, bone infection, immobility, a weak immune system, poor nutrition and a foreign body left in the wound. A wound care team will examine and measure your wound, check the blood flow in the area around the wound, determine why it’s not healing, and create a treatment plan.