"According to the American Orthopaedic Foot and Ankle Society, people take an average of 10,000 steps a day. High heels shift the force of each of those steps so that the most pressure ends up on the ball of the foot and on the bones at the base of the toes. (If you wear flats, the entire foot would absorb this impact.) A 3-inch heel -- most experts consider a heel "high" at 2 inches or more -- creates three to six times more stress on the front of the foot than a shoe with a modest one-inch heel.
As a result, heels can lead to bunions, heel pain, toe deformities, shortened Achilles tendons, and trapped nerves. In fact, women account for about 90% of the nearly 800,000 operations each year for bunions, hammertoes (a permanent deformity of the toe joint in which the toe bends up slightly and then curls downward, resting on its tip), and trapped nerves, and most of these surgeries can be linked back to their high-heeled shoe choice.
The problems can travel upward, too. The ankle, knee, and hip joints can all suffer from your footwear preferences. When you walk in flats, the muscles of the leg and thigh have an opportunity to contract as well as to stretch out. However, when wearing your high-heeled shoes, the foot is held in a downward position as you walk. This keeps the knee, hip, and low back in a somewhat flexed position, which prevents the muscles that cross the backside of these joints to stretch out as they normally would. Over time, this can lead to stiffness, pain, and injury. High heels can also cause lower back strain, because the heel causes your body to pitch forward more than normal, putting excess pressure on the back."