Hi, Purple bruising on the back of the knee can be caused by several factors, including trauma or injury to the area, bleeding disorders, or underlying medical conditions. The bright white spot you describe when pressure is applied is likely a sign of decreased blood flow to the area, known as blanching. This can be a concerning sign and should prompt further evaluation by a medical professional. Some possible causes of purple bruising and blanching on the back of the knee include: - Trauma or injury: A direct blow or impact to the knee can cause bruising and discoloration. This is usually accompanied by pain, swelling, and tenderness in the affected area. - Bleeding disorders: Some people may have bleeding disorders that cause them to bruise easily or bleed excessively. These conditions can be hereditary or acquired and can cause bleeding in the joints and muscles. - Deep vein thrombosis (DVT): DVT is a blood clot that forms in a deep vein, usually in the leg. Symptoms can include pain, swelling, and discoloration of the affected area. DVT can be a serious condition that requires prompt medical attention. - Vasculitis: Vasculitis is a group of conditions that cause inflammation of the blood vessels. This can lead to damage to the vessel walls, which can cause bleeding and bruising. Other symptoms of vasculitis can include fever, fatigue, and joint pain. - Medications: Some medications, such as blood thinners or corticosteroids, can cause bruising or bleeding. If your husband is experiencing purple bruising and blanching on the back of the knee, he should see a healthcare provider for further evaluation. The provider may recommend blood tests, imaging studies, or other diagnostic tests to determine the underlying cause of the symptoms. Treatment will depend on the underlying cause and may include medications, lifestyle changes, or other interventions. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician