bruise on knee

Knee injuries typical of falls, impacts, or friction against a hard surface. The knees are covered in bruises (hematomas), and the skin may be swollen with purple, blue, or yellowish patches due to damage to the subcutaneous blood vessels. There may also be superficial scrapes where the top layer of skin (epidermis) is worn away, sometimes with visible blood or serous fluid. The wounds can be contaminated with dirt or gravel, especially if the fall occurred on asphalt or rough ground.