Design of Cork and Injection Molded Heel Lifts
With this blog just beginning, I feel it might be important for the readers to get a better understanding of why our heel lifts are designed the way they are.
Thirty years ago when we started manufacturing our own injection molded heel lifts, we knew that about 25% of the height of the lift was lost if the measurement was taken from the back of the heel, since the inferior part of the calcaneus strikes the heel of the shoe approximately in the center of the radius of the heel counter, not at the back of the heel counter.
That is to say, the weight of the body is supported the approximate center of the heel-bone. In other words, if you have a tapered heel lift that is marked 9mm as its size, which measures 9mm at the very rearmost edge of the lift, you are only receiving about 75% of the effective height of the heel lift.
An article published in The Foot, September 2006, verified this concept. By using other vendors’ heel lifts measured at the most posterior part of the lift, they found that the actual amount of elevation increase was only 76.4%. of the nominal height.
Design of Cork Heel Lifts
Forty years ago the beveled cork heel lift was born. We felt that a slight bevel around the edge of the lift would be better because it would allow the lift to lie flat in the shoe and not attempt to curl up around the edge. Remember, the majority of shoes at that time did not allow you to lift the insole to slide a shoe pad or heel lift under it, much less remove the insole and replace it with a more comfortable one. Shoe components were glued and sewn together at that time.
Our cork lifts have an area at the advertised height at the center radius of the lift, then taper smoothly down into the arch of the foot, making a smooth indetectable transition underfoot.
Dense cork is an excellent material for in-shoe lifts. It is lightweight, and compresses very little. (Our tests reveal less than 1mm compression after a year of constant use). Our cork lifts have a smooth vinyl top covering to protect them from abrasion and prolong their life. Cork lifts are a particularly good alternative for fashion or dress shoes, due to their light weight, and the ability to put them on the top of the insole of the shoe. Also, the cork is just soft enough to feel a little better than other types of lifts when placed on top of the insole directly underfoot.
Cork lifts are not as durable as injection molded lifts, but when used in dress shoes, or permanently placed in a shoe, they really don’t have to be. The need for durability is only an issue if you are going to be changing the lift from shoe to shoe.
Design of Injection Molded Heel Lifts
When we designed the molds for our injection molded lifts, we made them longer than had previously been practiced, tapered them back to front on a long slope, and designed the advertised height at the center of the rounded radius of the lift. By doing so, the calcaneus rests on that area and the full mechanical advantage of the lift is transferred up the leg. Hence, if the patient needs 9mm of lift to compensate for leg deficiency, they are getting 9mm in height advantage from the lift.
The long taper of the lift into the mid foot makes a smooth and comfortable transition from heel strike to toe off when standing, walking, or running.The injection molding process, compared to pouring material into an open-topped cavity mold, ensures consistent height, with no voids or defects in the lift. It also requires having as many as 25 different costly chrome-plated steel molds to produce the various width and height combinations.
We use a latex free PVC (vinyl) material with a durometer of 50-60 which results in strength, flexibility, and no compression with use. Our lifts can be easily trimmed with a razor blade, scissors, or sander if necessary.
All of our heel lifts are available in several different heights (3mm, 5mm, 7mm, 9mm, and 12mm) as well as 6 different widths in order to accommodate any shoe size.
Greater than 12mm height in an in-shoe lift is simply not realistic; the wearer will walk out of the shoe and become prone to ankle injuries due to poor stabilization in the shoe.
The content of this Blog is designed primarily for use by qualified physicians and healthcare providers. The information contained herein should not be used as a substitute for the advice of an appropriately qualified and licensed physician or other healthcare provider. The information provided here is for educational and informational purposes only. In no way should it be considered as offering medical advice. Heel lifts should always be used after evaluation and prescription by a qualified health care professional.