I see it all the time that well-worn comfy pair of shoes that many of the patients come in with on a regular basis. I ask the patients how old are these shoes? They say years… but as I go into my explanation about comfort vs proper function and it doesn’t matter if you are talking about a running, dress or a casual everyday shoe. The research shows that about every 300 to 400 miles the shoes should be replaced, even though they may not seem to be worn out. Shoes will show small wear patterns in the heel and mid/outsoles that can cause pain, dysfunction and stress on your lower joints (Ankle, Knees and Hips) and spine.
As an 8,000 to 10,000 steps a day walker myself, my workout and dress shoes are replaced about every 3 to 4 months. While this may not seem financially reasonable, it is the best thing for your shoes and of course your joints and back. The reason for this is that shoes will show minor wear patterns due to the force is generated in the heel of your foot when it hits/scrapes the ground. There may be additional signs with large creases in the mid to outsole showing at the shoe is wearing out. You may have additional aches and pains that creep up in your feet, ankles, knees, hips and lower back this is indication as something is wrong. This is your body's way of telling you that the shoe has been past its prime and looks along with comfort can be deceiving. It doesn't matter if it is a running/workout or a dress shoe as all those miles add up on each of the shoes differently. Easiest way to do understand this is to try to compare a new shoe to the old one as it would just feel secure to the heel and stable.
As a chiropractor, there are different wear patterns that I look for. These are in terms of how the foot/heel hits the ground and one leg could be shorter than the other one (which is very common), which will show a different wear pattern on the heel.
Excessive foot mileage on a shoe can create abnormal compensations or wear patterns on heel and soles of foot that lead to stressors on your joints and spine this is just like a tire with different wear pattern on the tread. This causes pain, joint dysfunction or even re-injury. Not that you have to try to calculate your exact daily steps (Most phones have a App that does this), but just see how many steps you do in a day, multiply the numbers out for a week and then plan on getting a new pair of shoes depending on how many steps you do per day. Your feet and back will truly appreciate you taken a little bit better care of your body.