Asymmetrical leg function is known, for example due to the foot in human (http://dx.doi.org/10.1016/j.jtbi.2014.01.029) or due to inclined posture in birds (https://www.researchgate.net/publication/267932115_Trunk_orientation_causes_asymmetries_in_leg_function_in_small_bird_terrestrial_locomotion). In the second paper I mention we suggest that leg asymmetry is necessary for an inclined trunk to stabilize the trunk.

There are different methods of measuring the effective leg length during locomotion, none of which is the most correct one nor the wrong one, for example between hip-foot tip, between hip-middle foot or between hip-Center of Pressure (COP), or even between Center of Mass (COM)-foot. None of these methods are wrong; it's simply a matter of what question do you want to adress with these methods.

Article Trunk orientation causes asymmetries in leg function in smal...

First there are many factors to consider when limb length asymmetry is considered, pelvic obliquity is one and fixed adduced or abducted limb is the a second, as theses may cause apparent asymmetry. In day to day practice direct measurement or block method are best used. However in asymmetry less than 2 cm quantitative asymmetry measurement is mainly used -at least in our context here- only for medico-legal reasons. i hope understood the question well.

Excellent comments by both.

The key points that I am trying to make are:

1. The subject of asymmetry is so much bigger than LLD. That is why some with a small LLD have large symptoms and some with huge LLD have none.

My paradigm shift is that It is the existence of the symptoms of unequal limbs that need to be evaluated more than the cause.

All bees are insects but not all insects are bees!

A women carries her handbag, her children and groceries on one side. A person runs on an inclined circular road 10 miles a day in one direction. A sport or exercise is one side dominated creating a larger muscle mass left to right (think racquet sports). A person has a one sided injury (a tendo Achilles rupture). A person is born with scoliosis to the left side that shifts the center of gravity to one side creating the effect an LLD.

These and more cause a shift in the posture with compensation regardless of the length of the leg bones that cannot be discerned or treated by examining lengths of legs with x-rays.

2. Lopsidedness causes pathological shifts in sway, perturbation and balance. It causes problems with fascial plane orientation as well as CNS performance (try to spend a week with a 15 pound weight you carry on one side of your body}.

Most of us are lopsided and in need of balancing

The problems with asymmetry are caused by what I am calling "The Inclined Posture" of which LLD is but one factor.

We should be testing for the existence of this posture (FEJA Testing  --- see my recent publication) clinically and confirming with confirmatory testing (the existence of a one sided bunion or a one sided heel,knee or hip pain pointing to the longer functioning side, or asymmetry in muscle mass or n=1 having different shoe sizes or ???) and correct for that. We should be having less concern for why n=1 is tipped or lopsided on the frontal plane once diagnosed and more concerned with reducing or eliminating the lopsidedness.

I have been practicing this paradigm shift when dealing with lopsidedness for 35 years that clinically is very effective and may be valuable to millions while you are ordering radiography with metal rulers of the bones of the lower extremity or taking F-scans or ???.

I submitted my paper to Gait and Posture decades ago and was rejected because it was theoretical gobbledygook. Sorry this has taken so long to surface but await your responses. 

Dennis

Some years ago I noted the leg length changes that occur with common low back pain. These are accompanied with a dysfunction in anterior rotation of the innominates on the sacrum and changes in the height of PSIS.  I devised a method of measuring the height of the PSIS before and after correction with manual posterior innominate rotation. I noted a movement of the PSIS cephalad and laterally with dysfunction and caudad and medially with correction averaging 1-1.5 cm.  One extreme case with a 2.0 cm leg length difference measured 2.5 cm at the PSIS after correction. 

The cephalad PSIS movement also puts a vertical shear on the sacral x axis that will cause a separation of the ilial origin of the piriformis from its sacral origin at the superior margin of the greater sciatic notch and also of the ilial origin of the gluteus maximus from its sacral origin (on a line from beneath the PSIS across the butt to the trochanter)  This is palpable.

The primary location of pain in these cases is at the PIIS.

Reversible pelvic asymmetry is a commonly overlooked cause of low back pain and should always be corrected with a manual posterior innominate rotation, which gives immediate relief of pain and shortens the leg length. 

DonTigny RL:  Measuring PSIS movement. Clinical Management. 10:43-44, 1990

I investigated lower limb asymmetries in elite distance runners using MRI, trying to correlate asymmetries with the cost of transport, but I didn't find any correlation, probably because the asymmetries were very small. Only differences higher than 2 cm can influence the energetic. Here the paper if it can be useful also for the references maybe.

Anatomically Asymmetrical Runners Move More Asymmetrically at the Same Metabolic Cost PLOS ONE. http://dx.doi.org/10.1371/journal.pone.0074134

Article Anatomically Asymmetrical Runners Move More Asymmetrically a...

Take a look at my research on the Short Leg Syndrome. I believe you will find it very helpful.

http://www.iarpt.com/short-leg-sydrome.html

Professor Rothbart

One of these prerequisites is that ‘optimal’ calcaneal motion and pronation of the foot occurs and for this movement to be transferred to the tibia, femur and then further up the kinetic chain. Some advocates of this approach have attempted to reliably ‘map’ throughout the body the complex regional relationships even promoting causative ‘injury prediction’ based on ‘sub optimal’ mechanics further down the chain.

Some of the questions the critical mind may ask about this approach are:

“What is optimal movement to begin with?”

“Are deviations just normal variations?”

“Have sub optimal mechanics reliably been shown to be causative of injury or pain?”

“Does pain change our biomechanics or do biomechanical variations cause pain?”

Abstract

Several interactive pelvic axes occur during activities of weight bearing and ambulation. Flexion and extension of the symmetrical innominates occur on the sacral x axis with weight bearing. Normal asymmetric innominate rotation occurs on the innominate axis at the pubic symphysis during weight bearing with normal ambulation. Oblique sacral movement occurs on an oblique sacral axis concurrent with asymmetric innominate movement.

Acute and chronic low back pain is commonly caused by a bilateral symmetrical or oblique anterior innominate rotation on the sacrum on an acetabular axis, usually while lifting, bending, lowering, shoveling, sweeping, a pendulous abdomen, during pregnancy or with a postural forward head. The innominates are caused to sublux slightly cephalad and laterally on the sacral x axis at the posterior inferior ilia

c spine. This is a measurable movement that puts a rotational shear on the bilateral sacral x axis and separates the sacral origins of both the gluteus maximus and the piriformis from their ilial origins resulting in pain across the mid–buttocks into the trochanter, down the tensor fascia lata into the lateral knee causing piriformis syndrome, pain across the buttock from the PIIS to the trochanter, a sciatic neuritis or a pseudo sciatica.

In all probability true sciatica is probably not from the disk but rather caused where the sciatic nerve exits just below or sometimes through the compromised piriformis. A specific abdominal pain may also accompany acute or chronic low back pain as may an idiopathic scoliosis. An associated posterior movement of the ischial tuberosities can approximate the distal sacrum, loosen muscles of the pelvic floor, decrease kinetic tension on the sacrotuberous ligaments and cause some degree of incontinence.

Dysfunction is all initiated at the sacral x axes. This is corrected effectively simply with a manual bilateral posterior innominate rotation that reverses all and various symptoms leaving the patient free of pain. Many areas of dysfunction are described, but not all.

Ralph

“Does pain change our biomechanics or do biomechanical variations cause pain?”

The answer unfortunately is one or both on a case to case basis and one or the other is dominant in each case. It is the life work of any biomedical architect or engineer of the lower extremity to appreciate both and determine which are in play n=1.

If one has plantar fascitis from overuse (i.e Marathon Running), the pain will cause biomechanical compensations that predictably will affect the postural and performance chains.

I one has a grandmother and mother and sister with bunions, treating the underpinning biomechanical variations will deter or prevent bunion formation in that individual

Dennis

Does pain change bio-mechanics? Sometimes.

Do bio-mechanical variations cause pain? Sometimes.

With normal gait, the innominate on the side of the rising leg will rotate posteriorly, causing the sacrum to flex laterally, but will not cause pain. And the innominate on the contralateral side will rotate anteriorly, to lengthen the stride, but will not cause pain.

With relaxed standing and symmetrical innominates, if you shift your line of gravity anteriorly the innominates rotate anteriorly on an acetabular axis and the PSIS will rise and make the legs seem longer, but will not cause pain EXCEPT if the normal ROM is exceeded.

Richard:

I have an open mind about the validity and applicability of your posting until you define "normal" when referring to normal gait. Please define for us.

Clinically, my experience has been that each of us has a range of optimal functional gaits that is different from everyone else.

Furthermore, each of us changes optimal gait many hundreds of times a day that is different day to day and left foot to right depending on many variables.

I counter your statement with one of my own; "we are snowflakes not clones so when it comes to gait, there is no normal gait to pattern or measure".

Dennis

Excellent answer, Dennis. I don't believe anyone has asked me that before. I surely have not answered it properly.

How about calling it 'upright" gait to allow for the flexibility or lack thereof in the pelvis, which initiates various, optimal, functional, normal, human, upright gaits.

In comparing the movement of a snowflake with optimal, functional normal, human, military, upright gait, I fail completely.. How about a 'march' step or a goose step or normal human ambulation?

Cordially,

Richard

Dennis Shavelson

Anyone can "make predictions that [may] will affect the postural and performance chains."

The point is really is, how reliable are those predictions?

Have you seen my live, weight-bearing X-rays of pelvic movement in the extreme long straddle position, with counter-rotation, right and left, with each foot forward, with movement at the symphysis axis, oblique lateral sacral movement on the oblique right sacral X axis and oblique, lateral, sacral, movement on the oblique left sacral X axis demonstrating about 20 degrees or more of sacral movement?

I think it may be the first in vivo demonstration of 'normal' sacral movement.

Leg length inequality increases stress across the sacroiliac joint created by uneven ligament strain. Kiapour et al. examined various loads across the sacroiliac joint created by different amounts of leg length discrepancy and various physiological motions (spinal flexion, extension, rotation). They demonstrated that as the leg length inequality increases, mechanical alignment decreases and loads and peak stresses increase. Rotational shearing forces were show to increase on the side of long leg, and by a lesser amount, increase the compressive forces on the short leg side. (Kiapour A et al. J Orthop Res 2012).

Leg length inequality varies with pelvic obliquity. An anteriorly rotated innominate will cause the leg on that side to measure longer measured with the subject supine and non-weight-bearing . The iliac crest will measure higher when that subject is standing and weight- bearing.

A posteriorly rotated innominate will cause the leg on that side to measure shorter when the patient is supine and non-weight-bearing. The iliac crest will measure lower when that subject is standing and weight-bearing.

When the subject is erect, the pelvic ligaments are kinetically loaded and balanced. When the subject is standing the first innominate movement is posterior rotation which puts a posterior lateral stress on the sacrum. The lateral sacral stress initiates counter rotation to decrease loading stress on the femoral head with loading.

15. Gajdosik R, Simpson R, Smith R, DonTigny RL: Pelvic Tilt: Intratester reliability of measuring the standing position and range of motion. Phys Ther 65:168-174, 1985

19. DonTigny, RL: Measuring PSIS movement. Clinical Management 10:43-44, 1990

Ralph:

You ask: “What is optimal movement to begin with?

I instead ask: ”What determines optimal human movement in closed chain and where does that control begin?

Optimal Human Movement in closed chain begins from the ground up. It is a qualitative concept that currently cannot be measured or researched quantitatively at a high level. That is our common sandbox, like it or not.

The human movement system must have structural and functional reserves that can deal with stressful, potentially pathological stance and movement are required.

The CNS, the muscle engines, the proprioceptive system and the myofacial and soft tissue connective tissue system are all poorly or misunderstood and not capable of being high level evidenced.

Optimal Movement in closed chain begins foundationally with the feet meeting the ground. This fact (or let's debate that) defies high level, valid and applicable research. t

Once a foot is structurally too rigid (overvaulted) or too collapsed (undervaulted) when weighted; injury, performance issues, deformity and degeneration are predictable up and down the posture.

The segments of the foot must have be capable of being optimally posed and capable of both structural flexibility and rigidity, optimal ranges of motions and the ability to control them via muscle engine function and soft tissue balance and efficiency in order to perform efficiently and injury free.

Bio-architecture and Bio-engineering that seemingly defy Newton's Primary Laws are in play as well as variables in n=1's weight, age, sex, activity level, wearables and fitness and health levels that make developing cohorts for high level quantitative research almost impossible.

My work in foot typing and the inclined posture relies on qualitative data and the existing quantitative evidence that has served to develop improved research cohorts and clinical outcomes.

Foot Typing and TIP has been used by numerous clinicians and centers for decades as their starting platforms to improved clinical diagnosis and treatment protocols while you and others are waiting for 3 or more decades for consensus, well defined language (think optimal, normal, pronation, etc) and high level evidence to surface.

One thing I am confident of Richard. My predictions for prevention, performance enhancement, injury reduction and quality of life upgrades when t comes to human movement issues of the patient/client sitting in front of me is better than yours because that is what I have done in successful practice for 40 years.

Dennis

I did not ask. " “What is optimal movement to begin with? "

You asked. “ ”What determines optimal human movement in closed chain and where does that control begin?

My answer is that optimal human movement in a closed chain begins at the erect pelvis with a posterior innominate rotation.

Dennis Shavelson

”What determines optimal human movement in closed chain and where does that control begin?

Well of course it's the equal and opposite reaction law, could be termed, ground impact reaction force and so the Pelvis for example is way down the chain, in terms of 'beginning'.

First principles, you've heard of him, Issac Newton.

Of course that depends upon what you mean by control and how closed you want the chain?

It's more than that. The posterior innominate rotation causes a lateral sacral flexion, which initiates the counter rotation of the trunk, which, in turn, protects the femoral head from the forces of impact loading. All of this occurs prior to the leg lift, swing through and heel strike.

Richard Louis Dontigny

now that's an interesting point, is there any research showing what happens on with paediatric gait and if the priori weight-bearing gait action is learnt?

I have not investigated that, but I think it is built into the pelvis.

Dennis Enix

Similar shearing and compression forces are created at the level of the foot when there are inherited biomechanical foot type specific pathology that go up the legs to the pelvis and back that impact one or both legs, etc, on a case to case basis.

Loss of stability, support, strength, symmetry and balance of the feet as we stand or move affect one or both sides of the entire postural chain FROM "THE GROUND UP", not from "THE PELVIS DOWN" my colleagues.

Ralph Samwell

You keyboard:

"Well of course it's the equal and opposite reaction law, could be termed, ground impact reaction force and so the Pelvis for example is "way down" the chain, in terms of 'beginning'.

and add: "First principles, you've heard of him, Issac Newton".

1. Actually, there are two other forces that produce pathological moments that must be compensated when in closed chain to prevent injury, deformity and degeneration; the Earth's gravity and shoes in a civilized society.

2. I stated the primary laws of Sir Isaac. If I take equal masses of gold, feathers and a bird and drop them from the same height, the inanimate gold and feathers ground at the same time and the bird flies away seemingly defying Newtonian Physics. We must add secondary and tertiary laws of aerodynamics, etc to explain the birds biological magic trick.

When you add bio to architecture, engineering, mechanics, etc you enter a black hole that dampens & stagnates its research.

3. Is it from the Feet Up or the Pelvis Down? Actually the Pelvis is "way up" the chain in terms of 'beginning'.

We both have a bias here but yours is less scientific and evidence based IMHO and mine develops better cohorts and predictable outcomes. I openmindedly see the huge importance of yours and you seem more close minded towards mine

Collaboration is the way out of the black hole, my colleagues.

I welcome personal contact from any and all to discuss further.

Richard Louis Dontigny

You keyboarded:

"optimal human movement in a closed chain begins at the erect pelvis with a posterior innominate rotation"

Actually, your statement holds true only in open chain such as if we lived in water.

Optimal human movement in closed chain begins with optimal structure and function of the foot and optimal function of the muscle engines that work it.

That is the basis for my evidence based biomechanical theory called Foot Centering and the research it has and will continue produce with or without collaboration.

Dennis Shavelson

1. Agreed

2. Not so much a black-hole, (although philosophically probably true) biological life fits between the niche or goldilocks zones, between gravity and motion, repulsion and attraction. The human has an “anti-gravity suit.” We love to mechanicalise foot locomotion but the truth is, it’s a compromise rather than a thing, a zero sum game if you will. A balancing system between top down and bottom up forces. As human life exploits the space between those two forces but; “…Over and over again a violent struggle rages between these two basic aspirations Symbiosis and Autonomy … the very fabric of the drama of human existence.” Ruppert F.

In terms of Sir Roger Penrose, “function is the emergence of opposing forces” but function is not the forces themselves. The whole is greater than the sum of the parts. In medicine we love to pick on some joint and mechanical action as the source of dysfunction, (it makes us look clever in front of the patient) yet blithely ignore complexity and anatomical variant. A bias to look as clinical disease as the reason and a pattern and a diagnosis to be reeled out to other patients, rather than a symptom for that unique person.Truth is, just like nature, we tinker, we add a corrective orthosis and claim brilliance for our insight. We come up with a pet theory that works for that circumstance and then publish a paper. All we’ve really done is shift the burden of proof. We still don’t really know why it worked and ignore the times in which it doesn’t (or worse, come up with yet another pet theory as to why it doesn’t work on that anomaly). All one can ever say is, “it worked for that time and these are the possible reasons why and it may work again.”

3. Possibly the other way around? I take account of top down and bottom up, add them together and get zero, a much more open-minded approach. It leaves possibilities, it leaves emergence and therefore evolutionary creativity, which can lead to ultimate variability within the laws of physics of this universe. “The universe is not just stranger than we suppose, it’s stranger than we can suppose.” Or as Voltaire put it; “Doubt maybe uncomfortable but certitude is ridiculous.” Predictable outcomes is the academics bias but Penrose or James Gleick to name but two add in Chaos theory, some stuff just is random. A cohort of the ‘normal’ human being is bias; I prefer the overwhelming weight of evidence that this is a mutant planet with every known mutation and ecological niche, often in a single species.

Ralph:

1. ditto with one addition. We also have a "kryptonite-like gravity suit" that never-endingly and predictably cripples, deforms and sucks the life out of us from the ground up.

2. ditto

3. ditto

We have much more in common than not.

Dennis

You have a point, but I you may have missed the effect of the kinetic loading of the primary pelvic ligaments. This system will not work under water.

40. DonTigny, RL: The Sacral X Axis: Location, Structure, Movement, Parallel Kinetic Ligamentous Loading, Function, Biotensegrity Technology and Pathology. The Essential Pieces of the Low Back Pain Puzzle. (June 18, 2017). Available at SSRN: https://ssrn.com/abstract=2988680. This is a free site.

I believe you are overlooking the major effect of parallel and alternate kinetic loading of the ligaments on the function.

40. DonTigny, RL: The Sacral X Axis: Location, Structure, Movement, Parallel Kinetic Ligamentous Loading, Function, Biotensegrity Technology and Pathology. The Essential Pieces of the Low Back Pain Puzzle. (June 18, 2017). Available at SSRN: https://ssrn.com/abstract=2988680. This is a free site.

I am sure that my response, in that it makes a point, also inherently carries with it the potential for the reader to choose to take offense. Nothing is shared in the spirit of arrogance or petulance, but with the certainty of one who has smacked my palm to my own forehead over my own ignorance.

1. Newton never said "equal and opposite and identical". The ankle possesses DRL, or divergent reactive leverage. In the direction of gravity, it manifests as a class 2 lever. In the reactive direction known in physics by the term "normal force" it manifests simultaneously as a class 1 lever. Both must be modeled accurately in motion analysis.

Question: are these truths not self-evident? If so, then if any research draws any conclusion based upon modeling that excludes either type of leverage, is not that research merely validated by flawed premises, and thus its soundness cannot be assumed?

2. Pain leads to biomechanical changes. This was proved by Pohl 2015 trying to replicate an earlier gait analysis of lesser glute weakening and inquiring about compensatory trunk lean. While kinematic changes were noted in the earlier study, none were seen in Pohl. He told me that there was tremendous resistance to him publishing due to... well... due to people not knowing everything about everything. You see, the earlier study used painful hypersaline injections to weaken the lesser glutes, but Pohl used a painless nerve block. While the other study showed changes, there was no kinematic change in Pohl's subjects. Now, before everyone gets their collective knickers in a twist, understand that Jacquie Perry got it wrong. There isn't one gait paradigm; there are two. Just like the new Chevy truck with a V8 that can also run as a 4 cylinder depending on terrain, the human body has TDGC, or terrain-dependent gait configurations. Only on level terrain do we fully extend the hip and knee in normal gait. Both gastroc and TFL require full extension to be allowed to participate. Where was Pohl's study? In a gait lab on level ground. Have the subjects walk down a hill and things change drastically.

3. Asymmetry leads to biomechanical asymmetry. Whether LLD or muscle, there will be an impact. Give it long enough and Davis' Law can mess with you and cause pain. Bell 2013 looked at short transfemoral amputees and long transfemoral amputees. Both walked with the same gait efficiency, but the short limbs had more trunk lean. While Bell stuck with "compensatory motions are inefficient", her data proves that the truth is "compensatory motions effectively preserve gait efficiency". But here's the point... at what cost? Does the greater trunk lean of the shorter TF amputee lead to back pain sooner? We don't know because Bell had the wrong assumptions.

Gentlemen, one cannot use a linear process in a situation with reactive elements. And everything with gait reacts. We must engage in abductive reasoning prior to either inductive or deductive reasoning. In the words of Carlo Rovelli, the theoretical physicist, "Before measurements, calculations, and meticulous deductions, science is above all about visions. Science begins with a vision. Scientific thought is fed by the capacity to "see" things differently than they have previously been seen."

What are you gentlemen missing? Perhaps that biomechanics itself is limited in its vision. Page 491 of Neumann's kinesiology textbook tells us that with the hip, regardless of whether it is the pelvis or the femur moving, we see the hip osteokinematics in anatomical position. Perfect! You see the pelvis as a class 1 lever. Except... if you have the capacity for vision, you might turn your head sideways 90 degrees and see the femur as a class 3 lever.

And folks... if you've never done that, you don't know what you're missing. You see, the hip is not the class 1 lever espoused by the AAOS and the ASB. It is a UCL, or a unified compound lever, which is multiple levers that are simultaneously supported by a ball fulcrum. For is not the femoral head a circle? Why must you limit your vision to only vertical when the very model violates Archimedes' Law of the Lever (glutes attach to femur, which is the fulcrum-thus the distance value is zero. The hip is mathematically irrational allowing it to include only vertical forces).

Or perhaps it's that biomechanics only utilizes a single simple machine when there are six from which to choose. For the man whose only tool is a hammer, the whole world is a nail. For the researcher whose only tool is a lever... but there is also a wedge, a pulley, an inclined plane, a wheel and axle, and a screw. If your only tool is a lever, you must protect it, you must limit it, you must isolate it. This is the case with "closed chain" movement. Dennis Shavelson , you will find this JOSPT editorial fascinating Article Making jargon from kinetic and kinematic chains

Trust me... I know... because during transfemoral amputation, the IT band which holds everything in place is cut. Suddenly, the self-neutralizing horizontal forces acting at the hip manifest. And the answer of the AAOS was to remove the IT band and weaken the hip abductors in the name of "balance". Forever my patients have struggled missing 30% of hip power (Ryser 1988)".

Is there more? Yes... but I think I've said enough for today. With those facepalm epiphanies, I've come to be far more aware of unnecessary patient suffering.

My apologies if this appears disjointed. The flawed assumptions in biomechanics are so numerous that it makes it difficult to only address one. Suffice it to say that if your initial approach includes a fatal flaw, everything thereafter is vulnerable as well. While the actions of biomechanics are organisms... unless you are pushing against someone's foot instead of against the ground... those reactions are mechanisms and very different in nature than the organism. And the reactive nature of mechanisms, while foreign to most in healthcare, is all we know in prosthetics.

Thomas Cutler:

I sense that I have found a brother in arms in you.

I will respond to your posting one segment at a time.

1. Hypothetically, in a vacuum, if we drop three objects having the same mass, feathers, gold and a bird, the feathers and gold will land at the same time, and the bird will fly away. Biomechanics, bioarchitecture, biomedical engineering, etc, when researched and practiced and taught by engineers, architects, etc. will be full of flaws.

I can stop rolling down a hill anytime I want.

2. The misconception that if I want to learn to run fast, this task will be blindly supported by my brain, CNS, , peripheral nervous system, myofascial organ and proprioceptors is a crippling mistake wrong. They must be shut down, rebooted and given a new default to learn.

3.

Article The Inclined Posture (TIP): A New Clinical Entity

Dennis

Clinically I believe the 0.5 cm, instrumentally by x-ray on a squared slab even 1 mm. But the symptomatic cut-off is uniformly accepted as 1 cm. However, the instrumental value is always indicative compared to the clinic: there are patients who have pain with 0.5 cm and patients who do not have pain with 1.5 cm. Other factors to consider are essentially: valgus of the hindfoot, asymmetry of the pelvis, coxa vara / coxa valga and the presence of scoliosis.

Before you can comprehend the bio-mechanics of the pelvis you MUST have the sacral X axis, which is at the posterior inferior iliac spines. When the pelvis is symmetrical the X axis is transverse. When the pelvis is asymmetrical the X axis alternates obliquely with each step. The sacrum moves with lateral

flexion toward the side of loading to decrease loading to the femoral head.

Movement is about 25 degrees. I have X rays of the front of the loaded pelvis in the long straddle position demonstrating movement of the sacrum on the oblique

axis.

Gabriele Colo

By keyboarding "valgus of the hindfoot" you encourage the continued blind acceptance of the major myth/falsehood/unproven in the literature axium of lower extremity biomechanics, PRONATION that has been passed on for generations.

In reality, rearfoot valgus as a primary pathomechanical entity only exists in a modest 12-17% of all feet when typed using The Functional Foot Typing System. Classified the Flexible Rearfoot Functional Foot Type, calcaneovalgus has remained a poorly understood and relatively untreatable entity. The primary and most existing pathomechanical entity of lower extremity biomechanics is "varus of the forefoot" or The Flexible Forefoot Functional Foot Type which exists in almost 70% or more of all feet.

Dennis

It is years since I have commented on the importance of diagnosing and treating small amounts of limb length discrepancy.

With the increase in ankle, knee and hip replacements being performed, I am seeing more post op complications of these procedures causing a difference in the length of bone being removed and the replacement implant length causing changes in limb length asymmetry that need correction.

The Inclined Posture is working well in these cases.

Acute and chronic back pain is essentially all caused by a bilateral anterior innominate rotation , usually symmetrical (lifting, bending , lowering, shoveling, sweeping, pregnancy or a postural forward head) that causes the innominates to rotate cephalad and laterally at the PIIS. This is a measurable movement that puts a vertical shear on the lateral x axis points and separates the sacral origins of both the gluteus maximus and the piriformis from their ilial origins resulting pain across the mid –buttocks into the trochanter, down the TFL into the lateral knee causing piriformis syndrome and a pseudo sciatica.(4) In all probability true sciatica is probably not from the disk but probably caused when the sciatic nerve exits just below or sometimes through the compromised piriformis.

Dysfunction is all initiated at the sacral x axes. This is corrected effectively simply with a manual bilateral posterior innominate rotation that reverses all symptoms leaving the patient free of pain. Measurement of movement in the PSIS before and after correction with a manual posterior innominate rotation was from 1-1.5cm with an extreme of 2.5 cm in an acute SIJ dysfunction. Leg length is increased with anterior innominate rotation and decreased with manual posterior innominate rotation.

RichardTo say that LLD is ALL caused by innomate rotation reveals a fairly large lack of understanding of closed chain function IMHO

You would be correct if we libed in water or on the moon

GRF and gravity work from the ground up on Earth

Dr Sha

Asymmetrical anterior innominate rotation can result in a functional leg length discrepancy. This was the conclusion of a paper I published in the JAMPA. But I agree with Dr Shavelson that there are other etiologies for a FLLD.

• Rothbart BA 2006. Relationship of Functional Leg-Length Discrepancy to Abnormal Pronation. Journal American Podiatric Medical Association;96(6):499-507

Currently a discussion on AIS is running on the Podiatry forum. Your input would be appreciated. The thread is available at:

Adolescent Ideopathic Scliosis linked to Abnormal Pronation | Podiatry Arena ( https://podiatryarena.com/index.php?threads/adolescent-ideopathic-scliosis-linked-to-abnormal-pronation.112913/

Anterior innominate rotation will increase leg length usually from 1-1.5cm.

measured from the sacral x axis before and after manual posterior innominate rotation to correct. If the rotation is equal on each side the change in functional leg length will be equal

Richard: My point is that IMHO, often closed chain root cause treatment will be at least in part at the level of the foot.

What is your treatment for AIR and does it result in a cure or is treatment ongoing (needing skilled maintenance)?

Anterior innominate rotation is a common result of abnormal (gravity drive) (Rothbart 2004). In order to reverse this forward rotation of the innominates, you need to determine the cause of the abnormal pronation.

Both the PreClinical Clubfoot Deformity and Metatarsus Primus Varus foot structure (both congenital foot structures) will cause abnormal (gravity drive) pronation (Rothbart 2010).

Appropriately dimensioned proprioceptive insoles are used to effectively reduce the abnormal pronation in both of these foot structures. This does not involve an ongoing maintenance.

• Rothbart BA 2004. Postural Distortions. The foot connection. Online Journal of Orthodontics, May 10; 6(1): 1-8
• Rothbart BA 2010. The Primus Metatarsus Supinatus (Rothbarts) Foot and the PreClinical Clubfoot Deformity.Podiatry Review, Vol. 67(1):

Both Dr Rothbart & I agree that the innominate pathology is a compensation of gravity driven forces as the foot weights into the ground.

However, I disagree that these forces are pronatory in nature as Dr Rothbard suggests. Often, they are supinatory forces generated by the forefoot in the flexible forefoot functional foot typing system (my bias as I invented and patented this system (see diagram).

The key is that Richard does not understand weightbearing biomechanics and does not seem to wish to confront that.

Hi Dr Shavelson,

The foot types you have delineated are seen clinically, without a doubt. My question, what is the etiology of these foot types.

I have proposed a classification system based on the embryological development of the foot. The 4 genetic foot types are: Clubfoot Deformity, PreClinical Clubfoot Deformity, Primus Metatarsus Supinatus and Plantargrade.

In a pure ascending pattern (no descending disruptions), I believe the foot types you have described are compensations that occur in either the PreClinical Clubfoot Deformity or the Primus Metatarsus Supinatus foot structures.

Consider coming on the Podiatry forum. I have started a thread on AIS. Would very much appreciate your input. The URL is: https://podiatryarena.com/index.php?forums/biomechanics-sports-and-foot-orthoses.3/

The discussion is: Adolescent Ideopathic Scoliosis Linked to Abnormal Pronation

Genetic and Endogenous factors I would summarize, different for every n=1.

Grandma had bunions, mom had bunions, how do we keep her daughter from getting bunions?