Not all orthotics are created equal and in my experience, not many of them are done properly where the goal is to intervene with a biomechanical solution for poor foot function.
If you, as the customer, are going to lay down some serious money for a custom-made device, let's make sure you understand the two major factors to look for - full contact with the arches and body mass-matched resistance.
Full Contact
This means the shape of the orthotic matches the shape of all 3 arches - medial, lateral and transverse -while the foot is positioned in "neutral" (subtalar neutral). It should "fit like a glove" to the sole of the foot.
The only way to create a perfect foot-orthotic fit is to take a 3-dimensional cast. Walking across a pressure mat or tracing your foot on paper won't represent the vertical dimension!
Body Mass-Matched
This means that the orthotic device serves to resist the force of body weight as it is transferred through the arch with each step.
This does NOT mean however, that the orthotic should be so rigid that there is no flex in the orthotic at all. What it does mean is that there is enough resistance to reduce the overall vertical drop of the medial arch AND to reduce the speed with which the arch drops. These are the factors that allow the soft tissues (muscle, tendon, ligaments) of the lower limb to experience less stress and over time, less damage.
The above case study is a typical example.
The left orthotic is made of laminated rubber and foam. With figure tip pressure the entire medial arch can be compressed flat against the table (see video). And even if that were not the case, the arch height measures only 18 mm at its maximum (apex), whereas the patient's neutral arch height is 33mm.
Here's a quick self-assessment to see if your foot orthoses are doing what they are supposed to.
Test #1: place your orthotic on a hard flat surface like a desk. Using your thumb, press at the medial arch and see whether it is compressible. If it flattens without any resistance, it's likely undercorrective for controlling the passage of weight with each step.
If it is impossible to compress, then it's likely too rigid and this type often hurts to use.
An orthotic needs to allow some natural pronation as shock absorption.
Just like adage in "Goldilocks and the Three Bears", there is such a thing as "just right" when it comes to orthotic flexibility. They should be neither too soft nor too rigid!
Test #2: with the orthotic on the floor and your foot on the orthotic, raise your heel slightly (2") off the floor, bringing the orthotic along with the heel like it would be inside your shoe. Look to see if there is a gap between the orthotic and your arch. If the orthotic does not reach, nor maintain, that maximal neutral medial arch posture, then how can it control the arch's descent from the neutral position?
The role of the orthosis inside the shoe is to create an environment that mimics ideal foot posture. This, of course, assumes a few things such as lack of rigid foot deformity and willingness to wear the orthoses in appropriate shoes. The above example is for those with a pes planus ("foot flat" in latin) when they stand/walk but these sure-footed humans are amongst the vast majority (ie. 80% of people who come to my clinic). I'll touch on pes cavus (foot high) people in another article but similar principles apply as far as the testing for contact and optimal flexibility.
If after reading/viewing this post, and testing your current orthoses, you think you may not be wearing an appropriate set, then let's take a look. You have nothing to lose but a piece of flat foam in your shoe.
Be sure you put your feet in the right place, then stand firm.
Abraham Lincoln