Why Are My Knees Purple?

When we notice that our knees have turned purple, it is generally understood that this is due to external force applied to the knee, resulting in local tissue damage and injury to capillaries, causing bleeding. However, when these bloods are not absorbed promptly, they form bruises on the skin surface. Bruises on the knees can be treated with blood-activating and pain-relieving medications, and if not severe, they will not pose significant harm to the body.

1. Venous Compression: Venous compression can narrow or occlude the lumen, leading to obstructed blood flow and subsequent hematoma in the corresponding organs and tissues. For instance, hematoma in the lower extremities may occur due to compression of the iliac vein by a pregnant uterus.

2. Venous Luminal Blockage: This is commonly seen in venous thrombosis. Since veins have multiple branches, venous congestion only occurs when the lumen is blocked and blood flow cannot be diverted through collateral vessels.

3. Heart Failure: Left heart dysfunction caused by mitral valve disease or primary hypertension can lead to pulmonary congestion. Right heart dysfunction resulting from pulmonary heart disease can cause congestion in organs such as the liver, kidneys, and lower extremities, resulting in systemic congestion.

Macroscopically: Due to obstructed venous return, blood accumulates in dilated venules and capillaries, resulting in enlarged organs and tissues. Slow blood flow and hypoxia in the hematoma area lead to reduced oxygenated hemoglobin and increased reduced hemoglobin, giving the organs a dark red appearance.

Metabolism: Venous congestion prevents organs and tissues from receiving adequate oxygen and nutrients, reducing tissue metabolic rates and heat production, leading to lower temperatures in the affected areas. The hypoxic tissues have weakened metabolic functions.

Microscopically: Dilated venules and capillaries are filled with blood, showing hemorrhages and interstitial edema. The consequences of hematoma depend on the nature of the organ or tissue, the degree and duration of the hematoma. Short-term hematoma has minor consequences, while long-term hematoma can have more severe effects.

Long-term hematoma, also known as chronic congestion, can lead to atrophy, degeneration, and even death of parenchymal cells due to hypoxia, insufficient nutrient supply, and accumulation and stimulation of metabolic intermediates in local tissues. Proliferative interstitial fibrous tissue, coupled with collagenization of reticulated fibers within the tissue, gradually hardens the organ, resulting in congestive sclerosis.