by Edward S Glaser1 and David Fleming2*
1 – Founder and CEO of Sole Supports, Inc.
2 – Sole Supports, Inc.
* – Correspondence: firstname.lastname@example.org
We read Dr. Phillips letter regarding our article Foot Posture Biomechanics and MASS Theory in the November issue with careful regard. While our article had some defects the acts were not as egregious as they were made out to be. The letter was structured well with numbered questions in three different sections, and we would like to address them as such.
The first section addresses “some of the outright misstatements about the theories of Merton L. Root”
- We would like to thank Dr. Phillips for the scholarly references showing that our statement in the article is supported by some of the greatest minds in foot biomechanics, and is consistent with others who have been looking. We would like to thank Dr. Phillips for the historical correction regarding giving Root credit for making the observation that rearfoot varus predominates when the patient is in prone and held in “neutral” position.
- We chose the 17 measurements because they were the ones Dr. Phillips and Kevin Kirby showed had horrible inter-rater reliability. “Static” refers to the fact that the body is static on the treatment table as opposed to a dynamic study where the patient is walking, running, turning, jumping etc. The line “Root recommended taking 17 measurements called the Static Biomechanical Exam” should be edited to “Root recommended taking 17 measurements, now called the Static Biomechanical Exam” we apologize for the error.
- This is not only what Dr. Glaser was taught at NYCPM as Root biomechanics, but is a direct correlation between the biomechanical examination and the design of the orthotic. Measure 4 degrees of rearfoot varus and put a 4 degree post. This presumes 100% efficiency of the part of the orthotic and the foot, which is a physics impossibility. If treatment was aimed at stabilizing the midtarsal joint, it failed. This is due to the foot will collapsing its posture until something stops it. Much like John Weed’s seven theorems (allow us to credit Weed here although we know there were other authors) states that if the calcaneus everts more than 2 degrees, the heel will fall through into full pronation (with associated calcaneal eversion). By the time the midtarsal joint touches the orthotic, the pronation is almost complete; the foot is already in a collapsed posture. It was precisely because of the rigid materials Root chose (remember, he was a lab owner, like Dr. Glaser) he had to lower the arch to make the orthotics tolerable. However, as for the forefoot post, we would like to thank Dr. Phillips for the historical clarity he has provided and by pointing out that we gave to much credit to Root regarding therapeutic significance to forefoot posting. We were not trying to give a complete and accurate time line of Root’s life and discoveries, instead our purpose was to offer the practitioner an alternative paradigm to base their biomechanical decision making, backed by observation, physics, and patient outcomes.
- Dr. Phillips states that we made an accurate statement. The rest of the objections are difficult to tie in to that statement. Root’s other “neutral” positions are off topic, of course there are other joints in the foot. Many axes dictate the posture of the foot. All except the Subtalar joint are addressed in Root’s corrective device. Root surely knew of all the axes of the foot that influence posture, but he failed to address the postural collapse in his orthotic.
- We would like to thank Dr. Phillips for expanding on our statement, we see no misrepresentation.
- A.) In Lee’s article, Root describes the epiphany in the shower when he came up with neutral subtalar joint position and describes it as “the key to my being able to contribute to podiatry.” Kirby also choose the sub talar joint axis “…during many weightbearing motions, the foot can be effectively modeled as a rigid body with the calcaneus, cuboid, and navicular all rotating as a single unit around the talus at the subtalar joint axis”
Lee, W. E. (2001). 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 in podiatric medicine and surgery,18(4), 564.
Kirby, K. A. (2001). Subtalar joint axis location and rotational equilibrium theory of foot function. Journal of the American Podiatric Medical Association, 91(9), 470.
- B.) There are no relevant comments for this statement.
- C.) Allow a clarification, by “partially pronated” we are using MASS posture as a reference. We are stating that STJ neutral is approximately 1/3 pronated from MASS posture, which is the beginning of postural collapse. The rest of your comments are predicated on this misunderstanding.
The second section address, “some of the poor representation of the literature used to support the authors’ contentions that the theories of Root should be discarded.”
- Dr. Phillips states that they discarded Elftman’s theory prior to 1977, but it is stated in Root’s book, Normal and Abnormal Function of the Foot – Clinical Biomechanics Volume II, on page 80.
- Where the body’s momentum intersects the transverse plane of the sub talar joint, the joint has nothing to do with the fact that the force vector intersects the sub talar joint axis. Frictional moments are far more significant around the heel rocker axis than the sub talar joint axis. Hence the calcaneus “hits the ground in forward rolling motion.” Southerland’s seven theorems starts.
- We would like to thank Dr. Phillips for the historical information.
- In no way are we making the assumption that all ADLs require the same amount of pronation or supination. We are simply stating that, since every step is different and applies a different force. Therefore, one must look at a range of forces when performing calibration.
- Dr. Phillips is absolutely correct. Here is a link to the video: http://youtu.be/OapU4rr2WUM
- Dr. Phillips is correct, the references were double referenced, and Higbie was misspelled. Higbie et al had already tested almost every large central fabrication US custom orthotic laboratory and found that PAL’s orthotic as described made the greatest positive kinematic change. PAL was therefore selected so as to represent the best functioning Rootian orthoses on the market in 1999. According to actual data collected. If they had chosen a more representative Rootian orthotic the results would have shown even more difference.
The final section address, “ways the authors make outlandish assumptions, demonstrate poor reasoning, and write what can be best called “mechano-babble”.”
- The middle facet is on a shelf of bone that protrudes medially, the Sustentaculum tali. The middle facet would have negligible effect here regardless of its relative surface area. When there is no anterior facet there is considerable potential for hyper-pronation unless ligament strength is exceptional. The more vertical the STJ axis, the greater the torque will be applied by transverse plane rotation of the tibia. Who is measuring in the frontal plane only? Is this a criticism of Root? Dr. Phillips’ description of torque during propulsion is exactly what would happen if the foot was in an ideal posture. He is advocating that we should put the foot in its best posture for propulsion. We are also in full agreement that ligamentous strain is occurring when the posture collapses and are therefore attempting a simple, elegant solution. Thank you for pointing out the dangers of allowing the foot to collapse its posture.
- We are sorry that Dr. Phillips finds fault with Hammel’s study. We are not sure any of the authors are much different in their analysis of STJ motion even though most used skin markers to assist interosseous STJ motion analysis. Then Dr. Phillips goes on to state that Root agrees with us on everything. Dr. Phillips’ description is accurate and we agree with it. His statement does not disagree in any way with MASS Posture theory. Your description and Roots are sequentially the same as we described. Root states a slight amount of STJ rotation occurs prior to heel contact and the vast majority of postural collapse of the foot occurs after forefoot contact. That is exactly what the Hammel‘s article showed, and what we observed as well.
- The human foot has no reference coordinate system so we used two vertically oriented cushions of 1” thick poron and placed on vertically angulated plastic sheets affixed to the simultaneously narrowing sides of a Hewlett Packard paper tray from an old printer. It is built to center paper on a tray so each side is designed to move toward the middle equally. The medial and lateral surfaces of the calcaneus are covered with indentations of usually less than 3 mm in depth, thus making the selection of individual points for reference meaningless. Therefore, we chose a mechanically induced average of medial and lateral points. Any slight error induced by the mechanical averaging of the rough sides of the calcaneus are more than made up for by the large sample size in the study. This can also be done mathematically if the surfaces were imaged in 3D. This data has already been gathered using a specially constructed structured light 3D lofting system our engineering team built and programmed. We went back to the Smithsonian and imaged all six sides of the calcaneus on the specimens. We plan on publishing those findings within the next year, time permitting.
Like all studies of bones, which is the best way to assess the relative geometric positions of large numbers of articular facets, the ligaments are not present. Since the talus has no muscular attachments, its movement, within the limitations of joint capsule and ligaments, can be predicted by the direction and magnitude of forces applied to facets whose geometry is known. We disagree with Dr. Phillips. The rotational forces generated down the leg are generated by the trunk of the body ratcheting around the stance phase leg as the swinging limb advances. The most important thing to understand here is that the head of talus is experiencing a rotational moment to externally rotate with the tibia, but the talar head has a steep incline to climb while experiencing the full body weight of the patient as he/she passes through midstance. When the anterior facet is everted during postural collapse, resupination becomes much more difficult for the patient. Preventing the foot from reaching the depths of pronation with kinematic control of the foot’s posture, makes resupination almost effortless and the subtalar joint can then act to externally rotate primarily in the transverse plane. When you put the head of the talus on a level anterior facet, this prevents sagittal plane motion between the talus and calcaneus; thus facilitating efficient propulsion. The section of your criticism where you describe the medial and lateral displacement that occurs throughout the gait cycle is the core reason that mapping the singular STJ axis placement in one posture, taken with no real frame of reference, off weight bearing is a meaningless exercise. A person can have a medially deviated STJ axis in one posture and a laterally deviated STJ axis in another posture. Thus, we are lead to the conclusion that posture the key to controlling foot function.
- MASS posture orthotics are used to describe any orthoses which is made according to the principles detailed in the exact sentence quoted by Dr. Phillips. The physics principles of Leaf springs apply the same for single and multilaminate springs. The difference between single axis theories (like Root and Kirby) and Postural theory (Glaser and Fleming) is that in MASS Posture Theory, the geometry of the plastic shell is taken from a dynamic cast of the foot with a calibrated foam which evenly compresses the soft tissues while passing force through the foot in as close to an ideal gait cycle the individual can attain with their current ranges of joint motion. Often more aggressive correction can be achieved after the patient has functioned around a more elevated posture for a few weeks or months, so it is wise to choose a heat adjustable material. Root did have full contact between the foot and his orthotics but at a much lower posture. Our consistent experience has been that lowering the arch about 8 mm will cause arch pain that appears to be caused by the repetitive impact of the foot as it pronates into the rigid device. Arch fill is almost universal for Rootian orthotics, although, as you point out, it did emanate from plaster modifications that Root himself made to the cast.
We asses full contact in our lab with an F-scan. It is not perfect during all phases of the gait cycle, but it is a major improvement over the hard flat tilted plates that Merton Root called orthotics. We are sorry that your MASS posture orthotics were uncomfortable, but we do remember that you began modifying them immediately without even giving them a chance to break-in. We think this single failure can be attributed to personal bias.
In conclusion, Dr. Phillips is an expert on Rootian History. He told Dr. Glaser that he and his father attended, recorded and transcribed personally every lecture that Merton Root ever delivered. What this article does is give many of the pieces of the puzzle that we call foot biomechanics. It gives the clinician a viable alternative to Root theory that chooses to address the collapse of the foot’s posture rather than a series of off weight bearing static measurements that have neither inter-rater reliability nor correlation to the kinematics of gait. It is better to find the posture that most closely mimics the beginning of the foot’s postural range of motion, with the soft tissues evenly compressed and use that geometry for a calibrated leaf spring to resist collapse of the foot’s posture throughout the gait cycle. RCCT’s like E. Higbie et al, demonstrate the measurable positive influence MASS posture orthoses can have on the gait cycle. There are other labs that use the MASS geometry but no one that I know of has copied calibration yet, although it is taught in Dr. Glaser’s lectures and on videos posted on Youtube (solesupportstv) exactly how the device is constructed, and how the math is done to recreate calibration. MASS Theory, MASS Posture, MASS Posture casting technique, or even calibration is patented or trademarked, just as Root never trademarked “Neutral Position”. The Neutral Position of rotation around the STJ axis was his gift to Podiatry. MASS Posture is ours.
Edward S. Glaser, D.P.M
David C. Fleming