Have you always been flexible? Look up Beighton Score and see if Connective Tissue Disorder is the reason for your bruising. I am old and, although always flexible, did not know that I had the disorder until some related issues happened. If you can do the flexibility tests it is then possible that your knee is hyper-extended. I overused one leg after a bad operation and now have a knee that looks like your pic. The Xrays showed a total misalignment of the thigh and calf leg bones at the knee. Just had prolotherapy to tighten the ligaments within the knee and am hoping for excellent results.
Good luck finding your answers