Dark spots on the knees are usually caused by a hyperpigmentation that occurs when the skin is too thick or dry. You can get rid of these dark spots by taking time each week to give your knees the care that they need to stop looking so dark, dry and rough, and go back to looking supple and flesh-colored. Use items you likely already have to treat and remove your dark knee spots.
Cut a lemon in half, and rub the pulp and juice over the darkened spots on your knees. Avoid any open cuts or sores, as the acidity of the lemon will sting the skin. Leave the lemon juice on the knees for 10 minutes and let it stay on your skin as you proceed to the next step.
Exfoliate the dead skin from your knees. The darkness is likely caused by your skin becoming thick and dry in that area. The skin on your knees, elbows and feet is naturally thicker and drier than elsewhere on your body because of the amount of strain these areas go through. Use a store-bough exfoliating cream or mix one yourself from brown sugar and olive oil. Rub in circular motions and rinse away.
Rinse away the lemon juice and exfoliating cream. Pat dry with a towel, then apply a rich, emollient moisturizer that's especially formulated for extra dry skin. When the area has been coated, cover it with plastic wrap to make sure that the lotion is completely absorbed by the skin. When it has absorbed, remove the plastic wrap and discard.