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Spring mass theory orthotic casting: Debating Foot Centering Theory with Tissue Stress Theory

This occurs at or near the end range of motion in subtalar supination. Interval measurement of the angle of calcaneal facets: A historical postmortem study.

Matthew Cox
Wednesday, May 12, 2021
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  • Measuring calcaneal motion into eversion allows the examiner to determine whether a rearfoot deformity is compensated or uncompensated Figure A large portion of the time what stops pronation will be medial forefoot contact.

  • A power lifter, for example, may want an orthotic calibrated to resist his entire weight plus the weight he is deadlifting or squatting. Kirby, K.

  • In the future, there will be places and times when the impact of a podiatric biomechanical education and practice will be necessary to assess unsuccessful outcomes and alternatives to MASS, before, during or after using MASS.

  • I am comfortable with this as an accurate and understandable appraisal of Wellness vs. We're operating at fast turnarounds and are ready to take orders today!

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Pronation and supination are defined in orthoic the open and closed chains as rotations spring mass theory orthotic casting this singular axis. Such a spring calibrated to deliver an equal and opposite range of forces to those applied by the body, encourages the foot into a more functional foot posture that may reverse deformity. Biomechanics of the subtalar joint complex. Postural elevation makes further elevation easier and postural collapse makes further postural collapse easier. Only an approximation is necessary or possible.

Measurements taken of the geometry of the three facets on over calcanei in The Terry Castinf at the Smithsonian Institute yielded one consistent observation: when the anterior facet of the STJ is level in the frontal plane, the calcaneus is inverted [12]. Composite Leaf Spring Since the downward and deforming force of intermittent compression causes postural collapse, a corrective force would have to be applied in the opposite direction if functional change is desired. Pronation and supination are defined in both the open and closed chains as rotations around this singular axis. Posture is simply stepping back and looking at the foot as a whole and observing the way elevation of the longitudinal arches causes bones to nest into each other in a more closed pack position. Postural collapse is the cause of functional impairment in the majority of foot patients and often leads to pain, pathology, and deformity.

Repetitive over stressing of the soft tissues can orthptic to bony malalignments that we refer to as foot deformities; hallux abducto valgus or hammertoes. At this point the orthotic contacts the foot in the arch and the soft tissue compression dampen the final impact. There are two ways that such a leaf spring can be applied to the human foot. Huerta, J. As the downward force of the human body moves lateral to the foot, the propensity of inversion ankle sprain will increase due to a rotational moment created in that direction. This model concerns itself with the distribution of kinetic forces and their perpendicular distance to this one axis. Journal of the American Podiatric Medical Association99 5 ,

This is where a foot orthotic device comes in. Foot massager Bridget ThomasJul 5,in forum: Introductions. Oh let the man alone. Excellent success was attained in most cases with the reduction of symptoms that gained this model of foot biomechanics broad acceptance.

For example, a forefoot varus deformity of 3 degrees with a poor MTJ locking mechanism may be symptomatic, whereas an 8-degree forefoot varus deformity with a normal MTJ locking mechanism may not be. Glasers reply. Foam Impression. Daryl, I think I remember John Weed teacing that the calcaneus would stop at vertical. Thank you for your replies. Take care, Daryl.

  • Typically, foot orthotic orders will be back in your hands within two weeksand AFO braces are within three weeks.

  • MASS posture has several elements.

  • I think that Langer produced a pamphlet on some degree of predictativity with various Root types.

  • Application of a calibrated leaf spring to resist collapse of foot posture can often make early visible changes in the gait cycle. Whatever the rotational axis of the calcaneocuboid, the talonavicular joint will always find a parallel axis.

The Lower Extremity 2, 31 Perry, J. These orthotic casting, flat, smooth, invented, generic-shaped orthoses with their various theogy, skives, grooves, lumps, and bumps are simply herding the terminal tissue stresses around the bottom of the foot to mask symptoms with no appreciable change in kinematics. Proudly powered by WordPress. No singular axis can even begin to describe the motion that occurs during ambulation or simply the elevation and collapse of the arches of the foot. MASS posture has several elements.

As the foot goes into further elevation of its posture, there is a zone where, according to Orthotic casting, there is no significant rotation around the STJ axis in any plane [17]. You can find STJ neutral in a broad range of foot postures both in the open and closed kinetic chain. The talocalcaneal motion, which is a posterior and slightly lateral slide along the cone-shaped posterior facet, is accompanied by a small amount of rotation around the STJ axis. As the bladder expands, it fully contacts the orthotic and begins to flex it. Symptoms become less evident when the amplitude of each tissue stressing event is decreased by soft tissue compression. Subtalar pronation is not synonymous with postural collapse, but it is a predicating factor. Posture is the All Axis Model.

Learning Objectives

Inversion occurs ideally at heel strike. Gait analysis: normal and pathological function. Therefore, an essential element of capturing the foot in this elevated posture is that the soft tissues must be evenly compressed as they will be during use.

  • So much is lost in the world of the written blog word.

  • Jacqueline Perry describes the axis of translation as the heel rocker mechanism [15].

  • For larger limb length differences, knee flexion of the longer limb is often used to minimize asymmetry. References Root, M.

The thumb and index finger of the other hand grasp the fourth and fifth metatarsal heads, moving the foot casting an arc of adduction and inversion supination and abduction and eversion pronation. Isaac Newton supplied the answer with his third law of motion: for every action there is an equal and opposite reaction. Daryl, it would be helpful if you started out stating what the postulate is. STN is the point where the talar head is equally prominent anteromedially and anterolaterally. The viscoelastic plantar fat pad absorbs some of the energy generated between IC and LR.

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The reasoning behind this, is in physics, when a force is applied theory orthotic one side of an axis it causes rotation in one direction, as it moves to the other side of the axis rotation occurs in the opposite direction. Flexion can then be captured digitally either via liner encoder or optics. Hodgson, B. Therefore, subtalar rotation and postural collapse are independent events occurring at different times in the gait cycle. It stands to reason that it would similarly follow restored function in the direction of health and reversal of deformity.

Journal of Sport Rehabilitation spring mass theory orthotic casting, 15 1. Five, being the most rigid, is less than five degrees of total rotation of the forefoot on the rearfoot. The bouncing mechanism itself results in a confinement of the free parameter space where solutions can be found. At this point the orthotic contacts the foot in the arch and the soft tissue compression dampen the final impact. Conclusion Posture controls function. If we observe the foot at heel strike through midstance, we see a huge forward and plantar grade translation of the STJ axis.

NewsBot Mar 19, Their test was skewed to favor Glaser casting castiny Glaser really doesn't believe in forefoot varus or valgus deformities, he basically tries advanced body slimming cast such out. Goniometric measurements of the non—weight-bearing examination assess the rearfoot with respect to STN position, as well as STJ mobility, based on calcaneal positioning in the frontal plane. Glaser: I remain respectful of you and your work. The use of foot orthoses as an effective treatment tool for biomechanical dysfunction of the feet evolved during the twentieth century and continues to be the subject of research and technology.

I have to agree with Dennis here and in the past have posted proof of where Ed sells his insoles theroy chain shoe store pedorthists branded under a different www CBAS. Kirby, K. I sense that part of my edge comes from the fact that that you and others call for me to live in a well proven, black and white well defined biomechanical universe while allowing yourselves to live in an unproven one that allows for grey. Within the podiatric biomechanics community during the past fifteen years, there has been a gradual shift away from using the SJN Theory as a theoretical basis for mechanical foot therapy.

These low, spring mass theory orthotic casting, smooth, invented, generic-shaped orthoses with their various tilts, skives, grooves, lumps, and bumps are simply herding the terminal tissue stresses around the bottom of the foot to mask symptoms with no appreciable change in kinematics. Orthotkc of the muscles of the foot. The STJ axis exits the foot at the same point; the momentum down the leg similarly passes its force vector down the center of the dome of the talus thereby intersecting the STJ axis. Clinical orthopaedics and related research, What causes the downward force of the human body onto the orthotic? As foot posture elevates beyond the Dysfunctional Zone the anterior facet of the STJ approaches level in the transverse plane.

The bouncing mechanism itself results in a confinement of the free parameter space where solutions can be found. Flexion can then be captured digitally either via liner encoder or sprjng. Therefore, an essential element of capturing the foot in this elevated posture is that the soft tissues must be evenly compressed as they will be during use. The effect of 2 different custom-molded corrective orthotics on plantar pressure. The idea is simple. What causes the downward force of the human body onto the orthotic? The most flexible feet, that usually collapse the most, can rotate the forefoot around the fifth metatarsal more than 85 degrees and are graded a one.

As the foot reaches the end of its postural range of motion, ligaments are tightening up and the velocity masz final impact is slowing down. Obviously, body weight is a major factor. Sarrafian calls it the Acetabulum Pedis hip socket of the foot [10]. This allows us to hit the ground from any angle, forward or backward and apply the appropriate axis based on the direction of heel rotation with every step.

The closer the anterior facet is to level, the easier the subtalar rotation occurs and the rearfoot locks in the sagittal plane facilitating efficient propulsion. Search Search for:. Trotter, L. One way to grade foot flexibility is to rotate the forefoot around the fifth metatarsal.

Foot orthoses that attempt to elevate posture into this zone often cause medial longitudinal arch pain as the foot repeatedly thwory down to impact the orthotic. Microtrauma occurring in this zone of foot posture causes symptoms. Thus, this decreased the range of motion and parallelism of the axes, results in increased range of motion. Foot flexibility is another factor. A corrective force applied after the motion has occurred can only mitigate the damage caused by the impact. The STJ axis is placed in an orientation that passes through the major forces entering the foot at heel contact, other than the force of friction which is horizontal and causes the forward roll of the calcaneus. Foot flexibility can be measured in different ways.

Pronation and supination are defined in both the open and closed chains as rotations around this singular axis. This means that when the arch is raised, the first ray not only comes down and lateral, but additionally increases its purchase. This explains an important contradiction. During the last few degrees of postural collapse tissue stresses are highest. Low velocity impacts cause little or no damage to the car because the bumper dampens the impact.

  • Shavelson can be invited to produce a similar lecture. The foot and ankle complex has three major functions in the gait cycle: attenuating the impact forces, maintaining equilibrium, and transmitting propulsive forces.

  • MASS posture is an aggressive approach to foot biomechanics.

  • Place your order Continue Shopping. What I want to see from you some mathematical logic and not broad sweeping statements about the foot being centered.

  • Obviously, body weight is a major factor.

During the last few degrees of postural collapse tissue orthohic are highest. Thank you for that compliment. It will pronate until something stops it. When the STJ cannot adequately pronate to accommodate an inverted forefoot, an uncompensated forefoot varus is present. Who do you use for shipping? That's probably just a reflection of me rather than anything else.

Such a twisting would put more force on the first metatarsal head at toe off, per Root [1]. I've actually come to think in CKC, whenever the heel everts from perpendicular, the forefoot has to invert to the reaarfoot. Replies: 7 Views: 1, The foot has 26 bones and 35 joints, all of which move in some way. The examiner grasps the calcaneus in one hand, fully inverts it in the frontal plane until end ROM is achieved, and then takes a goniometric measurement. How do you know that those stipulations are true from the data. Foot flexibility is another factor.

Blocking any one component of triplanar motion in a single cardinal plane prevents movement in the other two planes as well. Hallux ortjotic HAV is a progressive, acquired deformity of the first MTP joint that eventually results in a valgus subluxation of the hallux. FC begins with a foot typing and no questions are asked until the foot type is known. Kind regards Mark Russell. I think you will find some articles showing prediction of certain of the Root measurements with certain pathologies.

The effect of 2 different custom-molded spring mass theory orthotic casting orthotics on plantar pressure. No singular axis can even begin to describe acsting motion that occurs during ambulation or simply the elevation and collapse of the arches of the foot. This simple grading system is not meant to be accurate. The feet that are on the flexible side of normal will rotate between 60 and 85 degrees and are graded a two. Composite Leaf Spring Since the downward and deforming force of intermittent compression causes postural collapse, a corrective force would have to be applied in the opposite direction if functional change is desired.

Such a twisting would put more force on the first metatarsal head at toe off, per Root [1]. At this point the orthotic contacts the foot in the arch and the soft spring mass theory orthotic casting compression dampen the final impact. Evolution of foot orthoses in sports. Application of a calibrated leaf spring to resist collapse of foot posture can often make early visible changes in the gait cycle. Differences between single axis and postural models of foot biomechanics are explored. Merton Root, John Weed, and Bill Orien [2] did a thorough analysis of the motions that occur in the foot, analyzed muscle firing patterns, and did a magnificent job analyzing many of the most common, and therefore important, biomechanical foot deformities.

Sarrafian, S. This always generates a spring mass theory orthotic casting of discussion and always receives good feedback. One way to grade foot flexibility is to rotate the cating around the fifth metatarsal. I also like using devices of the MASS position in those who have a large amount of forefoot supinatus as the position allows for maximum correction. The effect of 2 different custom-molded corrective orthotics on plantar pressure. Elftman, H. A foot orthotic is a very simple machine.

Theory orthotic casting Arch Supination Stabilization MASS posture is proposed as the geometry of a composite leaf spring that applies a calibrated, more evenly distributed, force per unit area opposing the postural collapse that occurs as the foot is intermittently compressed during ambulation. That would tell the manufacturer that the foot is more flexible, and thus, make the orthotic more rigid. Variability of neutral-position casting of the foot.

Lrthotic stationary arm of the goniometer is positioned along the medial first metatarsal and the mobile arm along the spring mass theory orthotic casting proximal phalanx of the hallux. If not rejected, the caster is a Master. He wants to have a play with Ed. Alternative compensatory motion, extrinsic to the STJ, is necessary to achieve weight bearing on the medial aspect of the foot. The theoretical model of biomechanical foot and ankle examination is based on the work of Root and colleagues.

  • I would refer you to Eric Lee for a very good discussion of the tautological definition of neutral position. Discuss controversy related to traditional orthotic theory.

  • Root recommended taking 17 measurements called the Static Biomechanical Exam [2].

  • Upgrade your orthotic lab to Kevin.

  • It is the combination of full contact redistribution of force per unit area eliminating hot spots and the lack of repetitive impact that allow such a spring to apply a rather large corrective force while remaining comfortable to most patients. Search Search for:.

  • What causes the downward force of the human body onto the orthotic? The foot can be graded from one to five [20].

Treatment was aimed at correcting what was viewed as a frontal plane deformity with frontal casying correction of the rearfoot and forefoot, called posts, designed to encourage the foot into a more neutral rotational position around the subtalar joint STJ axis. I propose that the locking mechanism of the midfoot is multifaceted. The posture of the foot is divided into zones of postural collapse. According to Dr.

I will make xpring following conclusions: 1 Root theory is not complete theory. You can choose mold management on the prescription or email us to set standards for your account. Shav, I was purposely aiming for a brief position statement focusing on the what more so than how, who and why. I come up with similar problems. He infers that in that respect, all theories are one and the same.

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Only an approximation is necessary or possible. Regardless, of what they taught, can you provide an explanation of why the heel should stop at vertical? It is a composite leaf spring.

  • STJ supination is a compensatory mechanism for both deformities. The TCJ must be maintained in a neutral to slightly dorsiflexed position while measuring to lock it in a closed-packed position and better isolate STJ motion.

  • Several lever arms in the foot increase and decrease to accomplish this. What are these forces?

  • Most clinicians do not keep track of their treatement success-failure ratio.

  • Whatever the rotational axis of the calcaneocuboid, the talonavicular joint will always find a parallel axis.

Trotter, L. The basic difference between single axis models, such as the Orhotic Neutral Model, and a postural spring mass theory orthotic casting is that single axis models, by definition, ignore the rest of the foot. Biomechanics of the subtalar joint complex. All of these models are posture based [13]. Symptoms become less evident when the amplitude of each tissue stressing event is decreased by soft tissue compression.

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Subtalar supination is not synonymous with postural elevation but is spring mass theory orthotic casting beneficial for efficient propulsion. In this situation ground reaction force is proportional to specific contact time and total displacement is proportional to the square of the step duration. This dampening can mask symptoms without making a significant functional change in the gait cycle. The STJ axis exits the foot at the same point; the momentum down the leg similarly passes its force vector down the center of the dome of the talus thereby intersecting the STJ axis. Publication types Research Support, Non-U.

Only a few parameters, such as the vector of the specific landing velocity and the specific leg length, are sufficient to determine the point of spring mass theory orthotic casting of the system. Five, being the most rigid, is less than five degrees of total rotation of the forefoot on the rearfoot. If the clinician is unsure of whether a patient is a one or three for example, it is best to report the smaller number. The soft tissues between the orthotic and the bones compress unevenly. As the foot goes into further elevation of its posture, there is a zone where, according to Hammel, there is no significant rotation around the STJ axis in any plane [17]. These measurements are performed in the same medium to get comparable soft tissue compression in both casts.

Orien, J. Unless you know something I don't The viscoelastic plantar fat pad absorbs some of the energy generated between IC and LR. I validated Dr Root's postulates, like so many of us, for many years with clinical success, until I found developed postualates that worked even better for me.

The ICCs for intertester reliability were. Variability of neutral-position casting of the foot. Quote: Dr. And that to me is the key: across this world there are any number of people putting forward their ideas on how to treat foot and lower limb problems. Gait analysis: normal and pathological function. Only Ed can truly know the reason for this but I don't think it takes a genius level I. I can appreciate it is probably clearer in your own mind but a times we can be too close to the wood to appreciate the trees.

Treatment was aimed at correcting what was viewed as a frontal plane deformity with frontal plane correction of the rearfoot theroy forefoot, called posts, designed to encourage the foot into a more neutral rotational position around soring subtalar joint STJ axis. How much vertical force should this leaf spring apply to the foot in an evenly distributed manner? Beyond the Functional Zone, there is a zone that is not always present, where the foot can be put into so much supination that it becomes laterally unstable. These measurements are performed in the same medium to get comparable soft tissue compression in both casts. During running and hopping animals use flat angles of the landing velocity resulting in maximum contact length. MASS posture theory is proposed, which is a plastic leaf spring that is in full contact with the foot in the highest posture that a person can attain at mid-stance with the heel and forefoot in contact with the ground and the soft tissues evenly compressed. A composite leaf spring, or orthotic, must begin to resist pathologic motion or postural collapse before that motion occurs.

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A, Talus; B, calcaneus; C, cuboid; D, the cuneiforms. WB does not rely on the orthotic device alone. Evolution of foot orthotics part 2: research reshapes longstanding theory. Also pictured is the triplanar axis of the subtalar joint.

The FINAL purpose of the device being primarily kinematic again spring mass theory orthotic casting are back to your Roots and calling for one protocol for all feet and you use the word "final" where I would use the word "momentary"thus facilitating LE kinetics to function within physiological parameters, as best as can be determined and taking into account other variables e. Some of the vertical GRF is attributed to acceleration of the centers of mass of the foot and shank of the leg. Clinical Biomechanics Corporation, Los Angeles, Join the most innovative team for access to resources and discounts that will benefit your practice! A foot orthotic is a very simple machine. Enjoy our support!

By profiling all feet into subgroups with common characteristic weaknesses and strengths, the practitioner can casying a more aggressive, tailored program intrapersonally. It says that if you were to do the same examination in a cross section of similar genetic pool that you should find the average person to have the same result as Root said they should. An ineffective locking mechanism at the MTJ is often more clinically significant than the absolute degree of forefoot deformity. For some people, the prefab comes so close to the shape of the neutral foot, you can't get much better.

Foot Ankle Online J. Effect of 7-degree spring mass theory orthotic casting varus and valgus wedging on rearfoot kinematics and kinetics during the stance phase of walking. He reports a statistically significant change in the angle of gait of less than 1. As the foot reaches the end of its postural range of motion, ligaments are tightening up and the velocity of final impact is slowing down. Dysfunctional Zone postures are lowered to pathologic zone postures by arch fill.

Interestingly enough, none of the literature reported used the Root lab except I believe Rich Blake may have used them for his initial paper. Please do. Tibiofibular varum values are larger in RCS than in the STN position because of the combined effects of osseous malalignment and varus leg alignment associated with compensatory STJ pronation in stance. In the normal closed chain STN position, the calcaneus is in 1 to 4 degrees of varus inversion. The orthotics are being used much like a car bumper.

  • The examiner looks for evidence of genu recurvatum or excessive knee flexion, navicular drop, talar bulge, and inadequate or excessive height of the longitudinal arch.

  • This slope correlates to the spring constant, which allows each orthotic to be calibrated. That same athlete will need a different pair of orthotics for his ADL.

  • Difficult for the lab to know if it is an accurate cast of the right posture I guess? Figure A, In relaxed calcaneal stance, compensation for a forefoot varus deformity is normally subtalar joint pronation, resulting in an everted calcaneus.

  • It attempts to restore as close to an ideal posture to the foot as each foot can tolerate with its individual anatomy.

Momentum mass times velocity is the third factor that affects the magnitude of the downward force of the body. Huerta, J. Adequate plantarflex of the first ray must be present for conversion from flexible forefoot to a rigid lever. I have reviewed most of the literature on orthotic therapy and find it to be quite variable in the reports.

Arising from the medial process of the calcanean tuberosity, it passes distally along the plantar aspect of the foot, then divides into five spring mass theory orthotic casting for its distal psring at the base of the proximal phalanges by the plantar pads. It requires a practitioner of biomechanics as a participant in the process. Jones, P. I probably should have published some myself. Early on, foot orthoses were used to redistribute plantar surface foot forces to alleviate discomfort in pressure- sensitive areas of the foot.

I will respond after dinner later this evening. I validated Dr Root's postulates, like so many of us, for many years with clinical success, until I found developed postualates that worked even better for me. One of the reasons why many podiatrists have moved away from the SJN Theory is due to some of the inherent problems and inconsistencies with this theory of mechanical foot therapy.

Clinical Biomechanics Boot Camps. Only an approximation is necessary or possible. The most flexible feet, that usually collapse the most, can rotate the forefoot around the fifth metatarsal more than 85 degrees and are graded a one. Flexion can then be captured digitally either via liner encoder or optics.

Functional hallux limitus disrupts the normal windlass mechanism previously described. Plantarflexion and dorsiflexion and abduction and adduction are the predominant movements around the oblique MTJ axis, with little concomitant inversion and eversion. Normal rearfoot position is one in which STN is 1 to 4 degrees of varus. Several important articulations of the foot talocrural, subtalar, midtarsal, first and fifth rays are triplanar; the axis of rotation in these joints is not perpendicular to any of the cardinal planes sagittal, horizontal, frontal of the human body. The STJ must have an equal amount of compensatory pronation to lower the medial condyle to the ground for a vertical calcaneus. It requires a practitioner of biomechanics as a participant in the process. Even Dananberg uses basic Root casting techniques modified by Langer with his kinetic wedges.

The orthotics are being used much like a car bumper. In this prthotic ground reaction force is proportional to specific contact time and total displacement is proportional to the square of the step duration. Journal of the American Podiatric Medical Association98 6 The most significant postural collapse occurs at this time. Higby measured the force distribution on the metatarsal heads at toe off [23].

Normally, first spring mass theory orthotic casting movement is at least one thumb width above and below the plane of the other metatarsal heads. Ready to order theoyr Kevin Orthopedic? How do you feel about words that clinicians use every day in practice such as healthy and fit and better? This model concerns itself with the distribution of kinetic forces and their perpendicular distance to this one axis. Jacqueline Perry describes the axis of translation as the heel rocker mechanism [15]. Figure Non—weight-bearing goniometric technique. I can send you my most recent review of the literature which I submitted last year as part of an NSF grant.

Describe effects of extrinsic and intrinsic deformities and of abnormal pronation on the function of the foot during the various phases of gait. Very interesting material! About Dr. A composite leaf spring, or orthotic, must begin to resist pathologic motion or postural collapse before that motion occurs.

This allows subtalar rotation to occur. This allows us to hit the ground from any angle, forward or backward and apply the appropriate axis based on the direction of heel rotation with every step. A force curve plotting flexion against pressure gives us a slope. As the downward force of the human body moves lateral to the foot, the propensity of inversion ankle sprain will increase due to a rotational moment created in that direction.

Orthotic casting may have been the first to have actually made the observation that foot posture controls its function. Hamel, A. Springer New York. One calibration method is explained. Measuring the upward force delivered by the orthotic is difficult. That does not mean that one position is right and one is wrong. The challenge now is to come up with better clinical assessments to derive the prescription variable of which position to model the foot in.

And if you know me, Dieter, I also use pre-fabs for some of my patients. In a spring mass theory orthotic casting posture the anterior facet of the STJ levels allowing transverse plane sprig of the talar head which carries with it the medial column of the foot which rides over the lateral column further restricting midfoot dorsiflexion. STN position is calculated to be at 5 degrees calcaneal inversion, one third of the distance from its fully everted position. The reasoning behind this, is in physics, when a force is applied onto one side of an axis it causes rotation in one direction, as it moves to the other side of the axis rotation occurs in the opposite direction.

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