Floating bones - Discussion

Correspondence with Steven Levin

Dear Tim,

Thank you for putting some of the arguments against ‘floating bones’ and for compression loaded joints in one place, http://hexdome.com/essays/floating_bones/, so they may be discussed in a reasoned and professional manor. Since you single me out as the main protagonist of biotensegrity then I feel obligated to reply. I hope you will see fit to post my response on your website.

As a practicing orthopedic surgeon, I, too, was a firm believer in what I had been taught during my training in orthopedics and biomechanics, that the bones in the body compressed one another, the skeleton was the frame upon which the soft tissues draped, the discs were cushions transmitting compression load from one vertebra to the next, etc. However, after a post-grad year studying anatomy with Prof. Michael Harty (internationally recognized anatomist) at the U of Pennsylvania, and at surgery, when I actually looked in joints and questioned what I saw, all sorts of problems arose in my mind and I had to do some rethinking. The questioning started early; the tensegrity part came years later. Lets start with the disks as you do.

Pressure is not the same as load. Pressure is omni-directional. The pressure in an automobile tire is the same whether the car is up on jacks or the full weight of the loaded vehicle bears down on it. Where the rubber meets the road is load, and has a direction, and the tire pressure has nothing to do with it, just the weight of the automobile. It is astounding to me that Nachemson didn’t know better and everyone else let him get away with it – ‘the emperor’s new clothes’. What was measured by Nachemson and, later, Wilke (in only one subject), was pressure and therefore does not really indicate what the load is on the inferior vertebra. I am not arguing that the pressure doesn’t change, just that pressure gives no indication of load and, therefore, tells us nothing about the load on the vertebrae. One also has to question Wilke’s work as in his one subject study, the pressure standing up from a chair is the same as when lying supine and throws into question any of his findings, no matter how they are interpreted. (It is always the exception that is the most important observation). Obviously, when going from lying to standing the muscle tone of the entire body increases, and this could account for the increased pressure in the disk as the pressure in all the soft tissues increases as the tone increases. If you stand up suddenly and the muscle tone does not get up to snuff fast enough, you may get orthostatic hypotension, a drop in blood pressure, and even pass out. Obviously, an increase in BP doesn’t hold you up, although a drop will make you fall. We must also recognize that the disk functions in quadrupeds (and when we crawl as infants) as a couple, connecting the two vertebrae, and discs of quadrupeds and bipeds seem to be structurally the same and, in fact, quadruped disks of pigs and sheep are used in modeling biped disks by many biomechanics studying disc mechanics. As you are aware, the mechanics of a pillar and the mechanics of a beam are quite different with different internal stresses. How could a disk evolve for quadruped function and instantly adapt to biped function the first day you stand as an infant? How could you use a pig disk and have any confidence that it represented a human disk function?

The Knee next.
As far as I know, there are no in vivo (live) studies of loads in normal joints and all the loads are theoretical and calculated and based on the assumption that these joints are bone on bone compression. I know, you say the menisci in the knee distribute the load, but I, nor anyone else that I know of, have ever seen a meniscus in a normal joint distorted by the supposed crushing loads that are calculated. Standing MRIs and arthrograms of the knee (xray opaque dye is injected that coats the surfaces) clearly show no distortion of the menisci (about as soft as your ear cartilage), which must happen if the body weight is squeezing down on them, and there is clearly a visible gap between the joint surfaces of a mm or two, an accepted phenomenon. The usual explanation for the gap is that the joints are held apart by hydrostatic pressure. First, if we accept that the joints are kept apart by hydrostatic pressure, then pressure is evenly distributed on all the joint surfaces (not this much medial and that much lateral, Pascal’s principle) so that any calculation showing more load on one side than another must be wrong. Second, since the synovial walls of the joint are not rigid like the cartilage-covered bone, they would blow out. The normal amount of synovial fluid in a knee joint is about 5 cc, but the joint can easily hold 150cc+, so there is a lot of room, and the hydrostatic pressure cannot be raised to support the calculated loads so the joint cannot be held apart by hydrostatic pressure. I myself, have loaded joints in vivo under direct vision and with the joints opened to equal pressure inside and out and demonstrated the space. Hydrostatic pressure can’t do it. The bones are discontinuous.

Another problem that is not even on the radar screen of most biomechanics is that the joints of the body are slippery slopes that are near frictionless. If the joint is horizontal and flat, one might make the case that the loads can be normalized (at right angles to the articular surface), but what if the joint is tilted? Most joints of the body are vertical or nearly vertical during some time of their functioning, (the facet joints of the spine, which supposedly bear 15-20% of the compressive load of the spine are vertical almost all the time). The proximal bone would slide off the distal bone like a skier on frictionless skis sliding down a vertical ice face. In these situations, mathematically, there is little or no compression across the joint. Just get into a semi squat and your hips are angled so that the center of gravity of your torso would spin you around your hip joint, your knee and ankle joints are angled greater that 450 and you would be sliding off them. Since none of the muscles in the sliding mass could stop you (it would be lifting yourself off the ground by your own bootstraps) you must fall on your face. It is possible that both systems, columnar loading and tensegrity, exist, but that is highly unlikely, as evolution would favor the most efficient and the most widely adaptable and the other would disappear. The compressive loading would have to be in very special circumstances, with the body perfectly aligned over the joints. Even breathing would be destabilizing and a fart would blow you across the room. As noted, there is no direct evidence, and by now there certainly should be if it were true, that the bones of the body line up as a column.

The several references you site are not scientific articles but simplified information blurbs for lay people that are not literature referenced. Several of them are trying to sell some procedure for profit, such as the very controversial artificial disc. I tried to dig into some of the statements and all I could find were the same old stuff based on ‘free body’ calculations and no in vivo studies to back them up. Free body calculations have been discredited in the biomechanics literature (Hatze) as they fail to account for the interconnectedness of the body, such as the feedback loops involving two-joint muscles that leave the ‘free body’ being studied. Huijing has shown that there is no such thing as agonist and antagonist muscles and that all the connective tissue in the body is interconnected ((continuous tension) and Knott-Tate and Levin have demonstrated that this interconnectedness extends into the interstices of bone.

None of this proves the biotensegrity model, but it does disprove the concept that joints are compressive weight bearing. I have lots of stuff that supports my thesis that the mechanics of biologic structures is tensegrity mechanics, too much to go into here. I had extensive discussions with Ed Applewhite a few years ago and he thought that what I presented made sense and fully accepted my thesis. I even had a brief discussion with Fuller about it and he was very supportive of the idea and said he had worked with Ida Rolfe on just that concept, although it was never fully developed by them. I am unhappy that a student of Fuller, such as you, would have difficulty following the logic and mechanics of biotensegrity. I would hope that I could supply enough information that you would accept the concept.

I hope this generates a scientific discussion, and if it does, I will be a willing participant.

Steve

Stephen M. Levin, MD, FACS
Ezekiel Biomechanics Group
8608 Dixie Place
McLean, VA 22102 USA
[snip email]
www.biotensegrity.com


Stephen M. Levin wrote:

> Pressure is not the same as load. Pressure is omni-
> directional. The pressure in an automobile tire is the same
> whether the car is up on jacks or the full weight of the
> loaded vehicle bears down on it.

That is not true. The road causes a deflection in the
lower tyre, which causes the air inside the tyre to
be confined in a smaller space - so its pressure increases.

This pressure increase is of critical importance in
supporting the car - without it the car rests on its rims.

> Where the rubber meets the road is load, and has a
> direction, and the tire pressure has nothing to do with it,
> just the weight of the automobile.

The if the tyre pressure is low, the tyre deforms,
increasing the pressure in the tyre and increasing
the area where it contacts the road, until the car
is supported pneumatically, or the rims hit the ground.

The situation with intervertebral discs is simpler in
some respects: the contact area with the bone is of
fixed area - so only the pressure varies, which it does
roughly in proportion to the applied downward force.

> It is astounding to me that Nachemson didn’t know better
> and everyone else let him get away with it – ‘the emperor’s
> new clothes’. What was measured by Nachemson and, later,
> Wilke (in only one subject), was pressure and therefore
> does not really indicate what the load is on the inferior
> vertebra. I am not arguing that the pressure doesn’t
> change, just that pressure gives no indication of load and,
> therefore, tells us nothing about the load on the
> vertebrae.

I don't see the problem. The discs have a fibrous element,
so modeling them as liquid-filled bags will underestimate
the forces they can apply in compression. However, they
/mostly/ behave like liquid filled bags - so obviously
the pressure in them is highly relevant.

> Obviously, when going from lying to standing the muscle
> tone of the entire body increases, and this could account
> for the increased pressure in the disk as the pressure in
> all the soft tissues increases as the tone increases.

Tension in the body may increase the forces in the
spine, meaning that 110% of the weight above a
given vertebrae must be supported.

There is nothing between the intervertebral disc and
the vertebrae on either side of them that could possibly
insulate either from the forces applied by the other -
they are joined straight on to one another.

As to the idea that the discs are directly compressed by
muscles - that seems pretty silly. What muscles? The
front of the spine joins straght onto the lungs through
much of its length - a region of negative pressure, since
the lungs are sucked onto the walls of the rib cage.
The muscles that curve the spine forwards are on
the front of the body - nowhere near the discs.

[snip]

> The Knee next.
>
> As far as I know, there are no in vivo (live) studies of
> loads in normal joints and all the loads are theoretical and
> calculated and based on the assumption that these joints are
> bone on bone compression. I know, you say the menisci in the
> knee distribute the load, but I, nor anyone else that I know
> of, have ever seen a meniscus in a normal joint distorted by
> the supposed crushing loads that are calculated. Standing
> MRIs and arthrograms of the knee (xray opaque dye is
> injected that coats the surfaces) clearly show no distortion
> of the menisci (about as soft as your ear cartilage), which
> must happen if the body weight is squeezing down on them,
> and there is clearly a visible gap between the joint
> surfaces of a mm or two, an accepted phenomenon. The usual
> explanation for the gap is that the joints are held apart by
> hydrostatic pressure. First, if we accept that the joints
> are kept apart by hydrostatic pressure, then pressure is
> evenly distributed on all the joint surfaces (not this much
> medial and that much lateral, Pascal’s principle) so that
> any calculation showing more load on one side than another
> must be wrong. Second, since the synovial walls of the joint
> are not rigid like the cartilage-covered bone, they would
> blow out. The normal amount of synovial fluid in a knee
> joint is about 5 cc, but the joint can easily hold 150cc+,
> so there is a lot of room, and the hydrostatic pressure
> cannot be raised to support the calculated loads so the
> joint cannot be held apart by hydrostatic pressure. I
> myself, have loaded joints in vivo under direct vision and
> with the joints opened to equal pressure inside and out and
> demonstrated the space. Hydrostatic pressure can’t do it.
> The bones are discontinuous.

The 'usual explanation' is that the knee menisci carry the
force - e.g.:

``Menisci
  These are cartilaginous elements within the knee joint which
  serve to protect the ends of the bones from rubbing on each
  other and to effectively deepen the tibial sockets into
  which the femur attaches.''

- http://en.wikipedia.org/wiki/Knee

We know that the menisci carry the force because of what
happens when they are surgically removed - e.g. the quote
from my original article:

``The important role of the meniscus in force transmission can
  be seen when the menisci are removed.

  If the menisci are removed, the forces are no longer
  distributed over a wide area of the tibia. Without the
  medial meniscus, the tibial contact area is decreased 50 -
  70%. This means the same forces from the femur are
  concentrated on a smaller area of the tibia.

  When the lateral meniscus is removed, there is a 45 - 50%
  decrease in contact area. This results in a 200 - 300%
  increase in contact pressure, which can eventually damage
  the cartilage on the ends of the bones. This can lead to
  degenerative arthritis.

  In the 1960s and 1970s, it was common to remove a damaged
  meniscus entirely. This frequently led to early degenerative
  arthritis in many patients.''

- http://www.leadingmd.com/patientEd/meniscus/overview.asp

I am not clear on where you have got the 'hydrostatic'
theory you mention from.

> Another problem that is not even on the radar screen of most
> biomechanics is that the joints of the body are slippery
> slopes that are near frictionless. If the joint is
> horizontal and flat, one might make the case that the loads
> can be normalized (at right angles to the articular
> surface), but what if the joint is tilted? Most joints of
> the body are vertical or nearly vertical during some time of
> their functioning, (the facet joints of the spine, which
> supposedly bear 15-20% of the compressive load of the spine
> are vertical almost all the time). The proximal bone would
> slide off the distal bone like a skier on frictionless skis
> sliding down a vertical ice face. In these situations,
> mathematically, there is little or no compression across the
> joint.

I've not encountered the idea that much weight is
supported by compressive forces across the facet
joints of the spine.

However, it is not necessarily correct to claim that these
joints are not in compression, just because they are near
vertical.

Most joints are usually held in compression by prestress
in the ligaments that surround them.

> It is possible that both systems, columnar loading and
> tensegrity, exist, but that is highly unlikely, as
> evolution would favor the most efficient and the most
> widely adaptable and the other would disappear.

That does not seem very relevant in the case of the human
spine. Humans have grown larger and assumed an upright
posture only in the last half-a-dozen million years - not
enough time for major anatomical rearrangements to a
structure as basic as the spine to take place. As a
result we suffer from all manner of ailments - lordosis,
kyphosis, sciatica, hernia, disc ruptures, etc.

Evolution in general shows little love for "floating strut"
tensegrities. What it /does/ seem to make extensive use of
are hinges and ball-and-socket joints.

My guess is that these are used for much the same reasons
engineers like to use them - they are simple, neat,
effective, strong, permit a large range of motion, and
require little maintenance.

> The compressive loading would have to be in very
> special circumstances, with the body perfectly aligned over
> the joints.

I don't see why. I don't see much wrong with the naive view
that joint surfaces in compression can resist forces applied
by gravity according to the sine of the angle they make with
the horizontal.

> As noted, there is no direct evidence, and by now there
> certainly should be if it were true, that the bones of the
> body line up as a column.

There are disc pressure measurements in a variety of
positions from many individuals. How much more direct
could you possibly get?

> The several references you site are not scientific articles
> but simplified information blurbs for lay people that are
> not literature referenced. Several of them are trying to
> sell some procedure for profit, such as the very
> controversial artificial disc. I tried to dig into some of
> the statements and all I could find were the same old stuff
> based on ‘free body’ calculations and no in vivo studies to
> back them up. Free body calculations have been discredited
> in the biomechanics literature (Hatze) as they fail to
> account for the interconnectedness of the body, such as the
> feedback loops involving two-joint muscles that leave the
> ‘free body’ being studied. Huijing has shown that there is
> no such thing as agonist and antagonist muscles and that all
> the connective tissue in the body is interconnected
> ((continuous tension) and Knott-Tate and Levin have
> demonstrated that this interconnectedness extends into the
> interstices of bone.

My first reference cited:

H-J. Wilke, P. Neef, M. Caimi, T. Hoogland and
L. E. Claes, Spine 24, #8, pp. 755-762, 1999.

Wilke's work is covered in this 1999 article:

''New in vivo measurements of pressures in the
intervertebral disc in daily life''

- http://calorierestriction.org/pmid/?n=10222525

My second reference cited the work of Nachemson - e.g.:

''Disc pressure measurements''

- http://calorierestriction.org/pmid/?n=7209680

I do not claim to have restricted my sources to
peer-reviewed scientific studies - but either
I or my sources did in fact cite a number of
these.

> None of this proves the biotensegrity model, but it does
> disprove the concept that joints are compressive weight
> bearing. [snip]

That is not true. The anterior column of the spine
certainly /does/ bear weight in compression - and it
is both well known and widely accepted that it does
so. Similarly with the knee joint.

Because of the significance of anatomy to personal
health and well being, I do not favour people
teaching their own personal unconventional theories
of anatomy - at least without prominent disclaimers.

The misguided notion that vertebrae are supported solely
by tensile elements has the potential to cause harm
by causing people to underestimate the compressive
forces in their intervertebral discs - and may
result in medical problems among those sucked in.

With such issues in mind, I encourage you to sort
yourself out and stop promoting these mistaken views.

Best wishes,
--
__________
 |im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply.


On Nov 13, 2006, at 7:52 AM, Tim Tyler wrote:

> Stephen M. Levin wrote:
>
> > Pressure is not the same as load. Pressure is omni-
> > directional. The pressure in an automobile tire is the same
> > whether the car is up on jacks or the full weight of the
> > loaded vehicle bears down on it.
>
> That is not true. The road causes a deflection in the
> lower tyre, which causes the air inside the tyre to
> be confined in a smaller space - so its pressure increases.

Easy to test. Go out to your auto and jack up your car and test the tyre pressure, then lower the car and read the tyre pressure again. The heart and soul of science is experimental proof, not just mathematical conjecture. If I am right, Nachemson and Wilke are wrong.

> The situation with intervertebral discs is simpler in
> some respects: the contact area with the bone is of
> fixed area - so only the pressure varies, which it does
> roughly in proportion to the applied downward force.

The nucleus of the disk is encapsulated in fibrous tissue and is very muck like a belted tyre.

> I don't see the problem. The discs have a fibrous element,
> so modeling them as liquid-filled bags will underestimate
> the forces they can apply in compression. However, they
> /mostly/ behave like liquid filled bags - so obviously
> the pressure in them is highly relevant

It is only relevant if contained pressure (omnidirectional) is related to load (sense, unidirectional).

> There is nothing between the intervertebral disc and
> the vertebrae on either side of them that could possibly
> insulate either from the forces applied by the other -
> they are joined straight on to one another.

All the bones are encased within a muscle-tendon-ligament-fascia network, It is the anatomy.

> As to the idea that the discs are directly compressed by
> muscles - that seems pretty silly. What muscles? The
> front of the spine joins straght onto the lungs through
> much of its length - a region of negative pressure, since
> the lungs are sucked onto the walls of the rib cage.
> The muscles that curve the spine forwards are on
> the front of the body - nowhere near the discs.

Near or remote, it is part of a network. All the fascial tissue. muscle, etc. are connected, experimentally demonstrated by Huijing et al, and it is impossible to contract only one muscle. The tone of the entire system, including the fibers of the disk are, all working as one. As the tone anywhere rises, the whole system increases tone.This is not theory but proven by experiment by a internationally recognized researcher.

> ``Menisci
> These are cartilaginous elements within the knee joint which
> serve to protect the ends of the bones from rubbing on each
> other and to effectively deepen the tibial sockets into
> which the femur attaches.''
>
> - http://en.wikipedia.org/wiki/Knee

That is theoretical conjecture with no experimental proof. No one has put a pressure gage or load tester (scale) in the knee. As I pointed out, the meniscus should distort and the space between articular surfaces, clearly demonstrable, must close if there is direct compression loading across the joint. Most joints do not have menisci to 'distribute ' the load, and the cartilage survives.
>
> We know that the menisci carry the force because of what
> happens when they are surgically removed - e.g. the quote
> from my original article:
>
> ``The important role of the meniscus in force transmission can
> be seen when the menisci are removed.

I removed many a cartilage in my early days of surgery, and most did very well. Some did not, but that proves nothing, as the knee was damaged before I did the surgery. Not every partial menisectomy does well, either.

> When the lateral meniscus is removed, there is a 45 - 50%
> decrease in contact area. This results in a 200 - 300%
> increase in contact pressure, which can eventually damage
> the cartilage on the ends of the bones. This can lead to
> degenerative arthritis.

Conjecture. Joints without menisci do perfectly well. Just about all joints in the body are incongruous, there is no perfect fit, so the contact surfaces would be very small and it would be like driving a spike into the soft cartilage. This was one of the reasons I doubted the conventional wisdom. At surgery, articular cartilage is very soft, indents easily, and cannot withstand shear forces.

> In the 1960s and 1970s, it was common to remove a damaged
> meniscus entirely. This frequently led to early degenerative
> arthritis in many patients.''

See above.

> - http://www.leadingmd.com/patientEd/meniscus/overview.asp
>
> I am not clear on where you have got the 'hydrostatic'
> theory you mention from.

It is in every text on biomechanics. Punjabi & White in Orthopedic Biomechanics give a whole chapter on it.

> I've not encountered the idea that much weight is
> supported by compressive forces across the facet
> joints of the spine.

I am quoting you here. One of the articles you site clearly states that 15-20% of spinal load is though the facets.

> However, it is not necessarily correct to claim that these
> joints are not in compression, just because they are near
> vertical.
>
> Most joints are usually held in compression by prestress
> in the ligaments that surround them.

Shake your wrist. Now tell me that the ligaments are pre-stressed and compress the joints and hold them stiff. If I shake you shoulders I could demonstrate the same in the neck and I could do the same at many joints, ankle, shoulder, etc.. Experiment, not conjecture.

> That does not seem very relevant in the case of the human
> spine. Humans have grown larger and assumed an upright
> posture only in the last half-a-dozen million years - not
> enough time for major anatomical rearrangements to a
> structure as basic as the spine to take place. As a
> result we suffer from all manner of ailments - lordosis,
> kyphosis, sciatica, hernia, disc ruptures, etc.

It is sink or swim. Either it works the first day, or it doesn't survive. It is nonsense to blame everything on upright posture. Any Vet will tell you, there are a lot of quadrupeds that have spine problems, too, including HNPs. Most people do not have significant backache, and when they do, it is usually self-limiting. We get pneumonia, asthma, bronchitis etc., a variety of heart diseases, etc. and no one blames the poor design of the lungs, heart, etc. The remarkable thing is that we do as well as we do. Most engineers would give their eye teeth to get a machine that lasts so long with such few problems, uses so little energy, and repairs itself.

> My guess is that these are used for much the same reasons
> engineers like to use them - they are simple, neat,
> effective, strong, permit a large range of motion, and
> require little maintenance.

There are not many engineered joints built of soft material like cartilage and bone, that can last 100+ years.

> I don't see why. I don't see much wrong with the naive view
> that joint surfaces in compression can resist forces applied
> by gravity according to the sine of the angle they make with
> the horizontal.

As the joints are essentially frictionless,any angle would cause the upper mass to slide. Bodies are accelerating to earth at about 9m/sec/sec. A dressed stone (CoF 0 .75) on stone will start sliding at about 35 degrees, a joint should slide at <1 degree. As the joint approaches vertical, as most joints do in some part of their normal function like squatting, bending, running, etc., the angle approaches 90 degrees and the sine of 90 degrees is 1, the mass is in free fall and there can be no compression across the joint. Anything less than 90 degrees and not horizontal will mean the joint load would be less that the mass weight. As I have noted, it is a physical law that a falling mass cannot be stopped except by an externally acting force. Therefore, the muscles within the falling body cannot stop the slide. The muscles below can only pull you down, destabilizing further. Friction at the joint would have to increase to a CoF of 1.0 and the joint would crush under such forces.

> > As noted, there is no direct evidence, and by now there
> > certainly should be if it were true, that the bones of the
> > body line up as a column.
>
> There are disc pressure measurements in a variety of
> positions from many individuals. How much more direct
> could you possibly get?

It is time to go out and put your car up on a jack.

> My first reference cited:
>
> H-J. Wilke, P. Neef, M. Caimi, T. Hoogland and
> L. E. Claes, Spine 24, #8, pp. 755-762, 1999.
>
> Wilke's work is covered in this 1999 article:
>
> ''New in vivo measurements of pressures in the
> intervertebral disc in daily life''
>
> - http://calorierestriction.org/pmid/?n=10222525
>
> My second reference cited the work of Nachemson - e.g.:
>
> ''Disc pressure measurements''
>
> - http://calorierestriction.org/pmid/?n=7209680

If I am right about the jack, the above references are worthless.

> That is not true. The anterior column of the spine
> certainly /does/ bear weight in compression - and it
> is both well known and widely accepted that it does
> so. Similarly with the knee joint.

Saying it is so does not make it so. It took 400 years to accept that the earth revolved around the sun, almost 100 years to accept evolution, etc. You are talking about flat-earth scientists. Where is the experimental proof. I have given proven reasons why it is not so.

> Because of the significance of anatomy to personal
> health and well being, I do not favour people
> teaching their own personal unconventional theories
> of anatomy - at least without prominent disclaimers.
>
> The misguided notion that vertebrae are supported solely
> by tensile elements has the potential to cause harm
> by causing people to underestimate the compressive
> forces in their intervertebral discs - and may
> result in medical problems among those sucked in.
>
> With such issues in mind, I encourage you to sort
> yourself out and stop promoting these mistaken views

Prove me wrong and the joint compression people right and I will retract my statements. I would expect the same from you.

Steve


Stephen M. Levin wrote:
> On Nov 13, 2006, at 7:52 AM, Tim Tyler wrote:
> > Stephen M. Levin wrote:

> > > Pressure is not the same as load. Pressure is omni-
> > > directional. The pressure in an automobile tire is the same
> > > whether the car is up on jacks or the full weight of the
> > > loaded vehicle bears down on it.
> >
> > That is not true. The road causes a deflection in the
> > lower tyre, which causes the air inside the tyre to
> > be confined in a smaller space - so its pressure increases.
>
> Easy to test. Go out to your auto and jack up your car and
> test the tyre pressure, then lower the car and read the tyre
> pressure again. The heart and soul of science is
> experimental proof, not just mathematical conjecture. If I
> am right, Nachemson and Wilke are wrong.

So, you choose to argue with basic mechanics. In my
book, that makes you ignorant.

> > ``Menisci
> > These are cartilaginous elements within the knee joint which
> > serve to protect the ends of the bones from rubbing on each
> > other and to effectively deepen the tibial sockets into
> > which the femur attaches.''
> >
> > - http://en.wikipedia.org/wiki/Knee
>
> That is theoretical conjecture with no experimental proof.
> No one has put a pressure gage or load tester (scale) in the
> knee.

Nonsense. Many people have done that.

I've put together a page of references to their work:

http://hexdome.com/essays/floating_bones/knee/

> Most joints do not have menisci to 'distribute ' the
> load, and the cartilage survives.

Most joints don't face the same degree of load as the
knee joint.

> > We know that the menisci carry the force because of what
> > happens when they are surgically removed - e.g. the quote
> > from my original article:
> >
> > ``The important role of the meniscus in force transmission can
> > be seen when the menisci are removed.
>
> I removed many a cartilage in my early days of surgery,
> and most did very well. Some did not, but that proves
> nothing, as the knee was damaged before I did the surgery.
> Not every partial menisectomy does well, either.
>
> > When the lateral meniscus is removed, there is a 45 - 50%
> > decrease in contact area. This results in a 200 - 300%
> > increase in contact pressure, which can eventually damage
> > the cartilage on the ends of the bones. This can lead to
> > degenerative arthritis.
>
> Conjecture. Joints without menisci do perfectly well.

The truth is different:

``Approximately 80% of patients with a whole meniscus removed
  develop significant arthritis in that compartment of the
  knee within 20 years.''

- http://www.sportsdoc.umn.edu/Patients_Folder/Knee/meniscal%20allograft/meniscalallograft.htm

> > - http://www.leadingmd.com/patientEd/meniscus/overview.asp
> >
> > I am not clear on where you have got the 'hydrostatic'
> > theory you mention from.
>
> It is in every text on biomechanics. Punjabi & White in
> Orthopedic Biomechanics give a whole chapter on it.

Well, I have never heard of it - and your presentation of
it seems totally ridiculous. Perhaps you are misrepresenting
the theory.

> > I've not encountered the idea that much weight is
> > supported by compressive forces across the facet
> > joints of the spine.
>
> I am quoting you here. One of the articles you site
> clearly states that 15-20% of spinal load is though the
> facets.

Which one? If that is a reference to:

``Furthermore, under normal circumstances, intervertebral
  discs support approximately 70-80% of axial loads imposed
  upon the lumbar spine, whereas the rest of such axial loads
  fall on spinal structures including, among others, the facet
  joints.''

``Biomechanical studies demonstrate that the anterior spinal
  column consisting of vertebral bodies and intervertebral
  discs bear most of the body weight in the upright position
  while the facet joints bear up to 16% of the axial load.''

...then you are misunderstanding the sentences by summarising
them as:

``the facet joints of the spine, which supposedly bear 15-20%
  of the compressive load of the spine''

> > However, it is not necessarily correct to claim that these
> > joints are not in compression, just because they are near
> > vertical.
> >
> > Most joints are usually held in compression by prestress
> > in the ligaments that surround them.
>
> Shake your wrist. Now tell me that the ligaments are pre-
> stressed and compress the joints and hold them stiff. If I
> shake you shoulders I could demonstrate the same in the neck
> and I could do the same at many joints, ankle, shoulder,
> etc.. Experiment, not conjecture.

The ligaments are pre-stressed and compress the joints. I
never claimed the joints were necessarily 'stiff'.

> > That does not seem very relevant in the case of the human
> > spine. Humans have grown larger and assumed an upright
> > posture only in the last half-a-dozen million years - not
> > enough time for major anatomical rearrangements to a
> > structure as basic as the spine to take place. As a
> > result we suffer from all manner of ailments - lordosis,
> > kyphosis, sciatica, hernia, disc ruptures, etc.
>
> It is sink or swim. Either it works the first day, or it
> doesn't survive.

A poor charactisation of the evolutionary process in
this context.

> It is nonsense to blame everything on upright posture.

I was not doing that.

> As the joints are essentially frictionless,any angle would
> cause the upper mass to slide.

A ridiculous assertion - since joints are bound together by ligaments.

> > My first reference cited:
> >
> > H-J. Wilke, P. Neef, M. Caimi, T. Hoogland and
> > L. E. Claes, Spine 24, #8, pp. 755-762, 1999.
> >
> > Wilke's work is covered in this 1999 article:
> >
> > ''New in vivo measurements of pressures in the
> > intervertebral disc in daily life''
> >
> > - http://calorierestriction.org/pmid/?n=10222525
> >
> > My second reference cited the work of Nachemson - e.g.:
> >
> > ''Disc pressure measurements''
> >
> > - http://calorierestriction.org/pmid/?n=7209680
>
> If I am right about the jack, the above references are worthless.

You've already dug your own grave on that issue.

> > Because of the significance of anatomy to personal
> > health and well being, I do not favour people
> > teaching their own personal unconventional theories
> > of anatomy - at least without prominent disclaimers.
> >
> > The misguided notion that vertebrae are supported solely
> > by tensile elements has the potential to cause harm
> > by causing people to underestimate the compressive
> > forces in their intervertebral discs - and may
> > result in medical problems among those sucked in.
> >
> > With such issues in mind, I encourage you to sort
> > yourself out and stop promoting these mistaken views
>
> Prove me wrong and the joint compression people right
> and I will retract my statements. I would expect the same
> from you.

I've proved you wrong many times over. You just refuse
to acknowledge it.
--
__________
 |im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply.



Tim,

Getting nasty and personal is not in the best interest of science. You raise reasonable questions that have every right to be addressed. I have reasoned responses to your challenges and I am familiar with the work you reference done on dead and disarticulated joints. I am interested in what happens in live joints as dead muscles work about as well as dead bowels; for example -- try testing how the muscles stiffen a wrist in a dead subject. So far, no one has figured out how to do that. I can address each and every point you raise and maybe I am wrong, and I am willing to put the biotensegrity theory to the test, but supposing I am right? I think that you, as a scientist, particularly one who is interested in tensegrity, would want to hear what I have to say and see if it is testable. I have an extensive background in biology, anatomy, surgery and a reasonable understanding of mechanics. I had a successful clinical practice of orthopedic surgery for 30+ years and have had several academic appointments and positions. What I propose is testable and, therefore, true science. Obviously, your mind is made up and you are not interested in a dialog, just a diatribe. If you keep this conversation civil, I can respond and you respond in turn. You arguments would become more valid if you could break down my arguments and counter arguments with testable facts. You cannot think that I have been writing on biotensegrity all these years without coming across your arguments before and addressing these issues as they have plagued me from day one. I want to hear your arguments and I think I can counter them and present a strong case, but I have no interest in doing so if the argument becomes personal, as you have made it.

Too bad -- it could have been fun and enlightening for both of us.

Did you jack up your car?

Steve

[snip by Tim Tyler of appended message history]


Stephen M. Levin wrote:

> Getting nasty and personal is not in the best interest of
> science.

Is that a reference to my describing you as 'ignorant'?

I had already tried pointing out your mistake and
explaining why it was wrong.

Perhaps I expected thanks - and an apology for wasting
my time with such nonsense.

Instead what I received was a failure to recognise the
mistake - and a message telling *me* to check my *own*
understanding.

At that point my message for you was necessarily of the
form: 'you do not have the faintest idea what you are
talking about'. IMO, there is no terribly nice way to
convey such a message.

I see little hope for the 'scientific discussion' that
you say you want when you make this kind of fluff up
in your own examples, and then go on to fail to
recognise your mistake when it is pointed out to you.

At this stage, my recommendation to you is to go away,
learn some of the basics about how pressure increases
with load in pneumatic systems. Then see if you can
work through your criticism of the relevance of the
work by Nachemson and Wilke, and see if you can make
any sense out of it.

> You raise reasonable questions that have every right to be
> addressed. I have reasoned responses to your challenges and
> I am familiar with the work you reference done on dead and
> disarticulated joints. I am interested in what happens in
> live joints as dead muscles work about as well as dead
> bowels; for example -- try testing how the muscles stiffen
> a wrist in a dead subject. So far, no one has figured out
> how to do that.

Being aware of these studies and failing to recognise their
impact on your hypothesis doesn't seem significantly better
than not knowing they existed to me.

> I can address each and every point you raise and maybe I am
> wrong, and I am willing to put the biotensegrity theory to
> the test, but supposing I am right?

Why would anyone bother supposing such a ridiculous thing?

> I think that you, as a scientist, particularly one
> who is interested in tensegrity, would want to hear what I
> have to say and see if it is testable.

I'm sure it's perfectly testable.

> I have an extensive background in biology, anatomy, surgery
> and a reasonable understanding of mechanics. I had a
> successful clinical practice of orthopedic surgery for 30+
> years and have had several academic appointments and
> positions.

I've been criticising your position. Your credentials are
of little concern to me - unless you attempt to use
argument from authority.

> What I propose is testable and, therefore, true science.

My criticism is not that your hypothesis is untestable.

My criticism is that it is evidently wrong.

> Obviously, your mind is made up and you are not interested
> in a dialog, just a diatribe. If you keep this conversation
> civil, I can respond and you respond in turn. You arguments
> would become more valid if you could break down my
> arguments and counter arguments with testable facts.

My arguments are valid as they stand, thank you.

> You cannot think that I have been writing on biotensegrity all
> these years without coming across your arguments before and
> addressing these issues as they have plagued me from day one.

How you came to your delusions is of little interest to me.

The fact that you have sustained them for so long represents
a poor reflection on your critical faculties, IMO.

> I want to hear your arguments and I think I can counter
> them and present a strong case, but I have no interest in
> doing so if the argument becomes personal, as you have made
> it. Too bad -- it could have been fun and enlightening for
> both of us.

It sounds as though you are out of here.

Goodbye, then - and best wishes,
--
__________
 |im |yler http://timtyler.org/ tim@tt1lock.org Remove lock to reply.


Tim,

i really urge you to test your tyre pressure, jack up your car, and test it again.

I am not so 'ignorant' that I would have made a public statement like that, so counterintuitive, without testing it myself.

Steve


On Nov 15, 2006, at 3:37 AM, Tim Tyler wrote:

> Is that a reference to my describing you as 'ignorant'?
>
> I had already tried pointing out your mistake and
> explaining why it was wrong.
>
> Perhaps I expected thanks - and an apology for wasting
> my time with such nonsense.

The deformation of the lower tyre into a more oval
cross-section reduces the volume enclosed by the
tyre - and thus increases the pressure.

Which causes the rest of the tire to expand until the volume and pressure were what they were in the first place.

You might also consider that, if I was correct with the tire pressure, I might also know something that you don't know about disc pressure.

Steve