Are You Aware Of The Twisted Plate Theory Of Foot Orthotics?

In 1999, I was asked to review a paper by Kogler and colleagues entitled, “The Influence of Medial and Lateral Placement of Orthotic Wedges on Loading of the Plantar Aponeurosis.”¹ The researchers studied the tension in the plantar fascia and which types of wedging (forefoot versus rearfoot and medial versus lateral) worked best to decrease that tension. As it turned out, lateral forefoot wedges reduced the strain in the central band of the plantar fascia better than medial wedging. 

Shortly after completing this article review, I started to make my own orthotics in my office utilizing an Amfit^® digitizer and the Amfit in-office CAD/CAM milling hardware. I made devices exclusively with ethylene vinyl acetate (EVA). I initially used a combination of medium- and high-density EVA. However, over time, I switched exclusively to high-density EVA. 

After having patients wear their EVA orthotics for anywhere from a few weeks to several months, I noticed that many of them came back with some persistent heel pain or other complaints. I also noticed most of these patients self-modified their EVA orthotics in a way I had never seen before with semi-rigid polypropylene devices. The EVA devices seemed to be twisting themselves somewhere between the forefoot and rearfoot. When I balanced their orthotics at the heel of the device on a flat surface, I could invariably see elevation at the lateral aspect of the EVA device.

This self-modification struck me as very odd and I asked a few people about this. Stanley Beekman, DPM helped me a lot back then and told me this was a common phenomenon with using softer material devices. He suggested that I just add some EVA under the lateral column of the existing devices to balance the forefoot to rearfoot relationship. Amazingly, that worked almost all of the time for these patients.

Many of you will think that this is counterintuitive. Perhaps you think that I should have added more of a varus heel modification to balance out this forefoot self-modification. I tried that with a few people and it did work anecdotally for me, but not as well as the lateral addition of the forefoot wedging. Patients often did not like the feel of the medial arch with an increased medial post versus a lateral forefoot post.

I then recalled the study by Kogler and colleagues, and things started to make a lot more sense to me. Over time, I found that I did not have to medial post my patients quite as much as I initially did in practice. The addition of lateral posting in the forefoot seemed to work amazingly well for me and my patients.

Little did I know that I had stumbled upon the “twisted plate theory,” which was first presented by Sarrafian many years before.² “In the plantigrade position when vertical loading and external rotation are simultaneously applied by the tibiotalar column on the foot, the hindfoot and the midfoot are supinated, and the forefoot is pronated. The medial longitudinal arch is higher, the foot is shorter, and the plantar aponeurosis is relaxed.”² To me, this makes perfect sense as does the aforementioned study by Kogler and coworkers.¹

Eventually, I wanted to figure out which patients needed to have lateral forefoot wedging and how much so I could get this addition right the first time and rarely have to make additional modifications to my devices. 

That will be the topic for my next blog post though and I hope that you will check back in for that.

Cheers!

Dr. Williams is a Past President and Fellow of the American Academy of Podiatric Sports Medicine. He is the Director of Breakthrough Sports Performance, LLC in Chicago. Dr. Williams has disclosed that is the Medical Director for Go 4-D and a consultant for HP FitStation.

References 

1. Kogler GF, Veer FB, Solomonidis SE, Paul JP. The influence of medial and lateral placement of orthotic wedges on loading of the plantar aponeurosis. J Bone Joint Surg Am. 1999;81(10):1403-1413.
2. Sarrafian SK. Functional characteristics of the foot and plantar aponeurosis under tibiotalar loading. Foot Ankle Int. 1987;8(1):4-18.