What is a prescription orthotic?
A prescription orthotic is a custom-made device that fits in your shoes. It is designed to force your foot to function in a more normal or neutral position while you are using it.
How does a prescription orthotic work?
Prescription orthotics can be challenging to make, especially for certain foot types. If your foot problem is caused by the mechanical issues described below, and your orthotic prescription is not made aggressively enough, your foot problem will not go away. If they are made too aggressively, they’ll hurt you, and you won’t wear them. The art of making orthotics is to get your prescription between these two extremes and right for you.
In order to understand how a prescription orthotic works, it helps to have a basic understanding of how a ‘normal’ foot should function. Your foot needs to perform two very different functions each time you take a step. As your leg swings forward, and your heel makes contact with the ground, your foot needs to be somewhat flexible, to provide shock absorption. As you move forward over this foot, it needs to lose this flexibility to become a rigid lever to propel your body forward. The way the human foot accomplishes these two very different functions is by changing the position of a joint which is right below the ankle joint called the subtalar joint.
Movement of the subtalar joint is called pronation and supination. These terms are used to describe motion at other joints in the body such as the wrist, etc. Generally speaking, (there are exceptions to this), the human foot is more flexible when the subtalar joint is pronated and is more rigid when it is supinated.
As you might imagine, people vary in how much they pronate and supinate at the subtalar joint while they walk. Some people pronate too much and have feet that are too flexible, which can place strain on certain tendons, ligaments, joints, etc. Other people supinate too much and have feet that are overly rigid and lack flexibility, placing strain on a completely different group of tendons, ligaments, joints, etc.
If you pronate too much at the subtalar joint, your prescription orthotic would most likely be designed to provide stability and force your foot into a more subtalar ‘neutral’position. To be successful, it needs to be rigid enough to support your body weight, it needs to fit the contour of your foot, and the available range of motion in the joints of your foot need to be considered when your prescription is written.
If you supinate too much at the subtalar joint, your prescription orthotic would most likely be designed to provide some flexibility and redistribute your body weight more evenly on the bottom of your foot.
A prescription orthotic can also be designed to simply redistribute weight-bearing forces away from painful areas on the bottom of your foot.
What type of problem can be helped by a prescription orthotic?
If too much pronation or too much supination at the subtalar joint are contributing to your foot or lower extremity pain, a prescription orthotic can be designed to limit this abnormal motion. This will often help to decrease or completely relieve your symptoms.
If your pain is caused by a particular area of your foot that is overloaded by weight-bearing forces, a prescription orthotic can often be designed to redistribute these weight-bearing forces away from that area.
How are prescription orthotics made?
There are a few different ways to make a prescription orthotic. If you went to 10 different doctors, you would likely end up with 10 different devices. In my opinion, the most accurate way is to take a non-weight-bearing plaster cast of your foot while it is held in a specific position. Certain foot problems require different casting positions. While you are being casted it is important that all the muscles in your leg and foot are completely relaxed so the casting position is not altered. This cast is then used to make a model of your foot which captures the forefoot to rearfoot relationship while your foot was held in the casting position. Modifications are made to this model and it is used to form the shape of your prescription orthotic.
What is the difference between an ‘over the counter’ arch support and a prescription orthotic?
There are many differences between an over the counter (OTC) arch support you might purchase in a store and a prescription orthotic. In certain cases, the OTC arch support would be the most appropriate choice, such as a patient with mild symptoms without any obvious mechanical issues, or an elderly person with symptoms caused by fat pad atrophy, etc.
OTC arch supports are produced in large quantities and are designed to accommodate a wide range of foot types. They are typically made of a softer material, and because of this, do little to alter the function of your foot while you walk. Many of these OTC arch supports are marketed to public as ‘orthotics’. If the arch support was already sitting in the store before you walked in, that is an OTC arch support.
A prescription orthotic is made from a mold of your foot and because of this, is able to be more aggressive. When you first start using an orthotic, you need to go through what’s called a ‘break in period’. I typically have my patients wear them 1 hour the first day, 2 hours the next day, 3 hours the next, etc.-adding an hour every day. The break-in period typically lasts about 2-3 weeks.
How long will they last?
Prescription orthotics are durable and will generally last about 5-10 years in an adult. In children, they need to be replaced when the child outgrows them. This all depends on the growth rate of the child, but typically occurs about every 1.5 to 2 years.
Are there certain types of shoes that I need to use them in?
Prescription orthotics work best in a sneaker or shoe that will hold your foot over the device. There is a sandal available that is designed to accommodate prescription orthotics.
