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?

   Obviously, the geometry of the orthotic should most closely mimic the geometry of the foot with the soft tissues compressed as they will be during orthotic wear when held in its most corrective posture. Otherwise, the foot will drop down and hit the orthotic with a certain impact force. Then the orthotic is limited to only dampening the final impact of the force of pronation itself, usually via soft tissue compression. This is often enough to relieve symptoms but no kinematic or functional change is detectable (without a lab full of biomechanical measurement equipment beyond the scope and availability of most clinical practitioners). Without functional change, deformity continues to develop. Any arch fill divorces the geometry of the orthotic from that of the foot.

   Full contact, on the other hand, allows for a more even redistribution of force per unit area. This eliminates hot spots and allows the application of a far greater corrective force while remaining comfortable to the patient. Therefore, arch height is irrelevant without proper calibration of the orthotic shell unless a brace is desirable. For example, an extremely high arched orthosis that is calibrated far too low (applying little upward force) will not be a high arched orthosis at midstance when the patient wears it.
Any prefab, as confirmed by numerous randomized controlled trials, can accomplish terminal impact dampening as well as most standard podiatric orthoses.

In Conclusion

Podiatry is at a decision point. Will we accept kinetic force dampening (as well as a drugstore prefab) or will we aspire to kinematic functional changes? When I speak of kinematic functional changes, I am talking about changes that influence function and thereby reverse deformity, improve performance, reduce injury and, by the way, also relieve pain.

   I believe it is the duty of every podiatrist to deliver the most functional device possible. This sets us apart as the custom devices we provide go beyond prefabs in a way that is uniquely and visibly functional. That is why I invented the first MASS posture orthotics that are calibrated to each person’s body weight, foot flexibility and momentum. These orthotics are custom to the foot (full contact), custom to the available postural range of motion, custom calibrated to each patient’s force parameters and custom designed for each patient’s shoes, activity level and function. That, as a complete paradigm, is very new.

   Dr. Glaser is the CEO of Sole Supports, Inc. He was previously in private practice for 13 years.

References
1. Glaser ES, Bursch D, Currie SJ. Theory, practice combine for custom orthoses. Biomechanics. 2006;13(9):33-43.
2. Trotter LC, Pierrynowski MR. The short-term effectiveness of full-contact custom-made foot orthoses and prefabricated shoe inserts on lower-extremity musculoskeletal pain: a randomized clinical trial. J Am Podiatr Med Assoc. 2008; 98(5):357-63.
3. Trotter LC, Pierrynowski MR. Changes in gait economy between full-contact custom-made foot orthoses and prefabricated inserts in patients with musculoskeletal pain: a randomized clinical trial. J Am Podiatr Med Assoc. 2008; 98(6):429-35.
4. Whitman R. A study of the weak foot, with references to its causes, its diagnosis, and its cure: with an analysis of a thousdand cases of so-called flat-foot. J Bone Joint Surg Am. 1896; 8:42-77.

Questioning the notion of inducing forefoot to rearfoot stability by pronating the midtarsal joint, this author summarizes key Root fundamentals, the effect of polypropylene use in orthotics and the relationship between arch flexibility and the midtarsal joint.

By Robert D. Phillips, DPM

As one looks at the basic postulates of Root theory in creating orthoses, Root made two very important fundamental points.1 The first was that there was a neutral position of the subtalar joint, very similar in description to a “non-pronated” state of the foot first described by Lovett and Cotton in 1898.2 This neutral position was not necessarily vertical to the ground. A review of the literature shows that Root’s first public paper was published one month before the paper by Wright and colleagues, who defined neutral subtalar joint position as one in which the heel was vertical.3,4

   The advantage of the Root neutral position was that it allowed people to be in a state of pronation or supination or neither when their heel bone was vertical with the ground. This meant that no longer was “heel vertical” the yardstick by which people were considered to have a normal functioning foot. It meant that some people with heel vertical function may complain of symptoms related to abnormal pronation and other people with heel vertical function may complain of symptoms related to abnormal supination.

   Root felt that when the subtalar joint was in neutral position, there was maximum congruity of the joint surfaces on the medial and lateral sides. This in turn would minimize the total tension in the ligamentous restraints and it would also create an equalization of the passive tension in the foot inverting muscles and the foot everting muscles.

   These conclusions are implied but not stated in the Root descriptions of subtalar joint neutral position. Since I was personally trained by Root in the Root casting technique, I can personally vouch that Root never advocated the palpation of the talonavicular joint for congruity when determining subtalar joint neutral position. The palpation of the talonavicular joint for congruity was more commonly taught by the East Coast biomechanics advocates. No one has shown that it is or is not identical to the Root position although it is highly likely that it is very close.

What You Should Know About Midtarsal Stability

The other basic postulate of the Root theory was that the midtarsal joint was in its most stable state when it was in its maximally pronated position.

   This was highly controversial in Root’s circles. Schuster outright rejected this postulate, stating that no joint should ever function at the end of its range of motion.5 He felt that the midtarsal joint should function in the middle of its range of motion. Due to these differences in philosophy, the West Coast practitioners measured the forefoot to rearfoot relationship with the midtarsal joint fully pronated. They also took impression molds of the foot with the midtarsal joint fully pronated. On the other hand, the East Coast practitioners measured and casted the foot with the midtarsal joint in a resting state.

   The Root idea about midtarsal stability was that by being fully pronated, the foot could easily transfer weight across the forefoot with the peroneals lifting the foot off the ground from lateral to medial. Root stated that if the midtarsal joint was not fully pronated, then the patient would be literally falling as the heel was lifting from the ground. Keep in mind that Root was saying nothing about the orthotic preventing the arch from collapsing.

   To the Root disciple then, the stability of the foot during propulsion was the key to prevention of much pathology, especially in the forefoot. Root followed the Manter concept of midtarsal joint stability. Manter illustrated that as the subtalar joint moves from a supinated to a pronated state, the range of motion of the midtarsal joint increased.6 Phillips and colleagues showed that this increase may be an exponential increase.7

   Root had noted that as the subtalar joint pronated, the midtarsal joint had to supinate on the frontal plane to maintain forefoot contact with the ground. The paper by Phillips and colleagues suggested that the frontal plane compensation of inversion of the forefoot for rearfoot eversion would be an exponential inversion from its maximally stable (i.e. fully pronated) position as the subtalar joint pronates in stance.7 Therefore, one could best maintain forefoot stability by making a mold of the foot with the subtalar joint in a neutral position and the forefoot maximally everted against the rearfoot.

   The model of forefoot to rearfoot mobility dependency on subtalar position suggested by Phillips and colleagues led to a subsequent work by Phillips, who proposed that the Root orthotic does not control the subtalar joint by producing a direct inversion moment on the calcaneus but instead controls the subtalar joint by an indirect method.7,8 For example, if the forefoot is prevented from inverting against the rearfoot in stance phase, then the rearfoot cannot evert relative to the ground.

Understanding The Impact Of Polypropylene In Orthotic Materials

The Root concept of foot motion stated that the subtalar joint must actually pronate some during early stance and failure to pronate will result in pathology as well.1 The Root orthotic made allowance for this pronation during contact by flaring the orthotic away from the medial arch. This flaring away of the orthotic was designed to bring the height of the orthotic medial to the medial band of the plantar fascia to the same height that the arch of the foot would be when it had pronated about 4 degrees.

   The Root orthotic relied on the use of a “rigid” material to have its effect. Root serendipitously had found Rohadur, which patients tolerated well when it was used with his casting and manufacturing technique. Unfortunately, this material was subsequently modified and has been totally unavailable from the manufacturing for the past 20 years.

   Today, most Root orthotics are made from polypropylene. Orthotic companies prefer this material because it is much cheaper than acrylics or composites. However, this material is also much more flexible than acrylics or composites. Therefore, it is very questionable whether polypropylene can hold the same shape when a patient stands on it in comparison to the shape a more rigid orthotic can hold when a patient stands on it.

Key Considerations With Arch Flexibility And The Midtarsal Joint

What I find particularly noteworthy is the fact that the medial arch is higher than the lateral arch. Accordingly, the lateral arch of the orthotic should be more flexible than the medial arch. If the lateral arch is more flexible, then the orthotic may not be able to fully pronate the midtarsal joint when the patient stands on it. Without the pronation of the midtarsal joint, the orthotic will be unable to prevent the subtalar joint from pronating, which will result in many orthotics being less than therapeutic.

   The response to this is the promotion of a system of casting the foot in which the forefoot is maximally supinated in the cast. The orthotic is then manufactured from a polyethylene material and is thinned out to allow the device to flex to the point where the midtarsal joint is pronated. If the orthotic does not flex to this degree, then it becomes a rock under the mid-arch and is very uncomfortable for the patient. I have clinically experimented with this type of orthotic but have found it to be as unpredictable as any other device it is purported to supplant.

   The concept of the midtarsal joint being maximally stabilized when it is in its fully pronated state has not been disproven. However, application of the Root casting system and current application of his concept using semi-rigid materials is suspect.
I recently reviewed an upcoming paper (submitted for publication), in which the authors demonstrated on bone replicants that pronation of the midtarsal joint tightens the ligaments across the midtarsal joint and creates stability of the forefoot to the rearfoot. The authors of the paper note that this would subsequently allow the foot to function as a second-class lever for propulsive purposes.

Final Notes

I am of the opinion that much work has yet to be done in proving whether forefoot to rearfoot stability can be induced by pronating the midtarsal joint. Then there is the work yet to be done in making a device that can produce this function during the midstance and propulsive periods of gait.

   Dr. Phillips is affiliated with the Orlando Veterans Affairs Medical Center in Orlando, Fla.

References

1. Root ML, Orien WP, Weed JH. Normal and abnormal function of the foot. Clinical Biomechanics Corp. Los Angeles, 1977.
2. Lovett RW, Cotton FJ. Pronation of the foot, considered from an anatomical standpoint. J Boston Soc Med Sci. 1898; 2(9):155-61.
3. Root ML. An approach to foot orthopedics. J Am Podiatry Assoc. 1964; 54:115-18.
4. Wright DG, Desai SM, Henderson WH. Action of the subtalar and ankle joint complex during the stance phase of walking. J Bone Joint Surg. 1964; 46A:361.
5. Lee WE. Podiatric biomechanics: an historical appraisal and discussion of the Root model as a clinical system of approach in the present context of theoretical uncertainty. Clinics Pod Med Surg 18(4):555-684, 2001.
6. Manter JT. Movements of the subtalar and transverse tarsal joints. Anat Rec. 1941; 80:397-410.
7. Phillips RD, Christeck R, Phillips RL. Clinical measurement of the axis of the subtalar joint. J Am Podiatr Med Assoc. 1985;75(3):119-31.
8. Phillips RD, Lidtke RH. Clinical determination of the linear equation for the subtalar joint axis. J Am Podiatr Med Assoc. 1992:82(1):1-20.

Additional Reference

9. Levitz SJ, Sobel E. Reappraisal of the negative impression cast and the subtalar joint neutral position revisited. J Am Podiatr Med Assoc. 1997; 87(1):193.