How To Tell When It's Time For New Orthotics
For many people, orthotics are temporary tools needed for recovery from an injury or for treatment for a condition that can be healed. For others, however, orthotics are long-term features that they need to use constantly. It can be difficult to tell exactly when those orthotics need to be replaced, however, because orthotic "failure" can be gradual.
Age, to a Point
Most orthotics have what you could call a shelf-life. They are expected to eventually wear out, so after a certain amount of use, you need to start checking the orthotics to see if they've reached the point where they need to be replaced. Something like simple shoe inserts might have an expected life span of a year or two, depending on how much walking you do, while shoes could last four or five years. At that point, you want to start inspecting the orthotics for signs if you haven't already seen any.
Note that an expected shelf-life does not have to occur on time; it can be late. If you take care of the orthotics, if you have several pairs that you alternate (e.g., regularly choosing from among five pairs of shoes, all with orthotic insoles, instead of using only one specific pair of shoes all the time), or if you don't walk that much, you could make them last a lot longer.
Say, however, that you want to ensure your orthotics are actually lasting as long as they're supposed to. Start inspecting them regularly after you've used them for maybe half their expected lifespan. Look for signs of wear, such as holes in insoles (you'll see these form at spots where your feet press into the insoles), and check the soles of the shoes, especially around the heel. Look for worn tread (replace orthotic shoes immediately if the tread has been smoothed out completely) and also signs of uneven wear, which may require a consultation with your doctor to ensure you have the correct step technique given your foot issues.
Fewer Noticeable Benefits or Increased Pain
Also a sign it's time to replace the orthotics is a decline in benefit. Say you have to wear insoles because of foot or leg pain, and you notice that you're having more pain, or at least less relief. That could be because the insoles are finally wearing out.
Orthotics that are well-made and well taken care of should last a substantial amount of time. However, do keep an eye on them to ensure you replace them promptly when they reach the end of their lifespan.