Point-Counterpoint: High Medial Arched Orthoses: New Innovation Or Older Technology?
Does maximum arch supination stabilization (MASS) theory change the way we think about custom orthoses? This author says the design of truly effective custom orthoses must consider orthotic height in relation to maximum corrective posture and the dynamics of individual gait.
By Ed Glaser, DPM
What do we mean by the term “high arched orthotics”? More importantly, to what is their height relative?
Maximum arch supination stabilization (MASS) posture is often misunderstood as being “high arched.” Certainly, in a flexible foot, MASS is higher than relaxed calcaneal stance position but that is not necessarily high relative to the ground. Most practitioners consider “high” or “low” in relation to the supporting surface, and this is a misconception.
The definition of MASS is the maximal amount of arch that one can comfortably achieve (following appropriate shoe break-in) at midstance with the heel and forefoot in full contact with the ground.1 Investigations have shown that foot orthoses based on this corrected position (or posture) provide relief of lower extremity musculoskeletal pain and improved economy of gait.2,3 In some individuals, this position may be quite high and in others, it is quite low in relation to the ground.
It would make much more sense to talk about the amount of “height” an orthotic has in relation to the most corrective posture. In other words, place the foot in the posture of optimal function and then determine how low you will allow the foot to drop before capturing its geometry for the manufacturing of orthotics. How much will you allow the foot to drop from optimal posture before it contacts the orthotic and a corrective force occurs? Most orthotics made today — especially those with a biomechanical model focused only on kinetic force distribution masquerading as tissue stress — are quite low in relation to the optimally corrective posture.
In 1896, Whitman made an important point that the “weak foot” is not necessarily a flatfoot.4 The weak foot has dropped from its correct “attitude” or posture to a point where its function is adversely affected. Naturally, Whitman tried to restore the foot to a more functional posture. As he stated, “The object of treatment is to change the weak foot, not only in contour, but in habitual attitudes and in power of voluntary motion to those of the normal foot, because a cure is impossible until function is regained.”
What You Should Know About Orthotic Arch Height And Individual Gait
Secondly, at what point in the gait cycle should one consider the height of the arch of an orthotic? If you are looking at the orthotic as it sits on a shelf, it may have one height. If you look at the orthotic as it exists during a particular step at midstance, it may be completely different. In the case of Whitman’s brace, being made of 18- to 20-gauge steel, the geometry does not change appreciably.4 That is the nature of a brace.
When an orthotic has a more flexible material, the posture may vary with the amount of force acting upon it. In the case of MASS posture orthotics, the shape will be considerably different when acted upon by the forces of body mass and differentially resisted by foot flexibility and momentum. That is why MASS posture orthotics are calibrated to deliver a range of forces that, to the greatest extent currently possible, overlap the range of downward forces exerted on the orthotic by the human body. Preferably the body’s downward force is slightly greater than the orthotic’s upward range of forces. This allows the orthotic to flex with the foot, eliminating disuse atrophy and allowing for functional control.
A better understanding of foot function, combined with engineering principles, would allow one to view the orthotic for what it actually is: a spring. This spring, usually of some sort of plastic (but not necessarily), is trying to apply a corrective force to the plantar surface of the foot. The foot has succumbed to the force of gravity and collapsed to a variable extent depending on its architecture, relative flexibility and geometry (among other factors).
So what geometry allows the application of the greatest corrective force while varying the spring constant (or flexibility) of the device?