Hello,
Your symptom is indicative of arthrofibrosis, though you have only mentioned of a dark spot on the knee and not on how you got it(trauma,
injury, minor surgery, etc). Arthrofibrosis may cause
stiffness of the knee or leg, it may limit your motion and cause substantial pain. It is due to excessive amount of scar tissue that forms around the knee. You are suggested to get clinically examined by an orthopedic and get required blood and imaging tests done.
Arthrofibrosis can be treated with corticosteroid injection and NSAIDS.
Physical therapy is equally effective. Sometimes, the treating doctor may suggest surgery or
cryotherapy. However, other medical conditions that can cause similar symptoms are RA, OA, get anti-CCP, CRP,
ESR, etc., done to detect if you have RA or OA.
Take care. Hope I have answered your question. Let me know if I can assist you further.
Regards,
Dr. Nupur K., General & Family Physician