Floating bones

The idea

Stephen Levin is one of the proponents of the idea. He explains it as follows:

The support system of the spine, and indeed the remainder of the body as well, is a function of continuous tension, discontinuous compression, so that the skeleton, rather than being a frame of support to which the muscles and ligaments and tendons attach, has to be considered as compression components suspended within a continuous tension network.

The author developed a model of the spine in which the bones are not in contact with each other - and instead are supported by a tensile network, presenting it with the following abstract:

The commonly accepted 'tower of blocks' model for vertebrate spine mechanics is only useful when modeling a perfectly balanced, upright, immobile spine. Using that model, in any other position than perfectly upright, the forces generated will tear muscle, crush bone and exhaust energy. A new model of the spine uses a tensegrity-truss system that will model the spine right side up, upside-down or in any position, static or dynamic. In a tensegrity-truss model, the loads distribute through the system only in tension or compression. As in all truss systems, there are no levers and no moments at the joints. The model behaves non-linearly and is energy efficient. Unlike a tower of blocks, it is independent of gravity and functions equally well on land, at sea, in the air or in space and models the spines of fish and fowl, bird and beast.

He seems to show some understanding of how radical his proposal is:

A rigid, axial-loading, gravitationally oriented support system cannot be utilized as a model for animated structures, including the human spine. A model based on Buckminster Fuller’s tensegrity icosahedron, which demonstrates the principle of continuous tension, discontinuous compression, may also be utilized to demonstrate the structural integration of the body. All our previous concepts of biomechanics of the body will have to be reassessed in relation to the model and our therapeutic approaches to the musculo-skeletal system will have to be revised.

What about the fact that it is a well known anatomical fact that bones in the spine and legs bear weight in compression downwards?

Apparently, Stephen has been present at operations, and observed that the bones in quesion do not touch each other when axial compression forces are applied:

Although some of the rigid components of a tensegrity system may "kiss," it does not mean that they are in compressive opposition to one another. Axial loads were applied to joints in live subjects under anesthesia during surgical intervention for a variety of conditions. Joint studies included the knee, ankle, elbow and metatarsal-phalangal joints. In our studies at no time could the articular surfaces of these joints be forced into contact with one another as long as the ligaments remained intact. Although the study may lack elements of sophistication, it is readily reproducible by any surgeon.

If there is no phyiscal contact, it is hard to imagine how compression forces could be transmitted.

The spread of the idea

Instead of what we're used to, which is a brick sitting on a brick sitting on a brick - and that's how you make a building. With tensegrity structures, the bricks, the sticks, float in a sea of rubber bands and they stay where they are because of the balanced tension between the rubber bands.

In the past, we have thought of our bodies as a stack of bones with the muscles hanging off of it like the cables of a crane. And it's not that way - the bones float in the soft tissue. It's those tensegrity structures that give us a geometric model to see how that works.

Stuart Bell explains the appeal of the idea as follows:

Most often we think of structures and build structures as one segment piled on top of another supported by gravity, for example brick homes. Compressional thinking is deeply ingrained, due perhaps to an easy experiential knowledge of this phenomenon from early childhood. Even the word structure is derived from the Latin struere which means to heap up or pile up. As a result, we unconsciously think of our bodies as built like that, as compressional structures, where the segments of the body stack one on top of another and where the bones are compressed directly against one another. This model works pretty well but it lacks finesse in describing all of the characteristics of human structure and movement. Many of us take on a “compressional” look in our bodies and postures. Our weight often looks passive and heavy. We look tired, as if gravity were not the ally it can be but an arch enemy instead.

Using Tensional Integrity as a model for bodies, where gravity acts as a friend, offers a beneficial alternative. Such a structure depends for support on a tensional-fabric- network where bones float in this sea of fibrous connective tissue and where the fabric in turn is seen to float in an ocean of fluid called the ground substance. Buckminster Fuller’s posits that such structures are more efficient in many ways, requiring a minimum of building material. [...]

When we conceive of ourselves as built by compression, the image could leave us with a heavy sense or feeling. In this sense gravity could be considered mostly as a downward force and perhaps the enemy. We might think of our aches and pains as local incidences, due to accidents, and localized structural failure and not be able to see the structure as a whole, not treat the whole body-mind continuum. We might become focused on single areas and lose our overall, connectedness perspective. We might also expect to have lots of problems where these compressional elements meet, at the joints and not look for causes from further afield.

The ubiquitous bone, muscle, fulcrum, and pulley model that pervades current thinking has served as a useful model when used within its bounds. But, improperly understood this model causes us to demand support from our bones and spine which is not healthy and causes much suffering in human spines and joints. Perhaps tensegrity can help.

Imagine our cells and the structure of our bodies all relying on a Tensional matrix for their Integrity, structure, support, well being, and communication. In the body we call this matrix connective tissues. The connective tissues respond to forces by sharing tension throughout the entire tensional fabric of the body, just as do the structures you see modeled here in the pictures below. Tensions, aches, and pains we feel in one area of our body connect everywhere in the body fabric, and they are often caused at some other surprising and unexpected locations. Gone are the days when working on separate parts alone will do without considering the effect upon the whole. The whole system all the way to the cellular and nuclear levels needs be addressed. In structural integration we see that proper organization in connective tissue leads to a balanced body and adds vibrancy to our cells.

Right. I can imagine how one can see gravity as the enemy, compression as its weapon and floating-strut tensile structures as salvation.

Problems

On that front there can be no mistake - the idea is a load of utter nonsense.

It is not accepted by the medical profession or the scientific community. Instead, it is promoted by a few enthusiasts - who seem to have skipped over attempting to gain scientific respectability for the idea - and are instead marketing it bodyworkers - perhaps a group identified as being scientifically naive and open to swallowing new-age claptrap.

Vertebrae do not 'float in a sea of tension'. At least not unless you are hanging upside down from a tree. Instead, they bear down on each other in compressive stacks.

Measurements of intervertebral disc pressure indicate that the pressure depends strongly on whether the subject is standing or is supine:

Disc Pressure Measurements Prove That the Pressure on the Disc is 11 Times Greater When the Patient is Erect

Another study - looking at L3 rather than L5 confirms this:

"The main function of the disc is mechanical. The disc transmits load along the spinal column and also allows the spine to bend and twist. The loads on the disc arise from body weight and muscular activity, and change with posture (see figure 6.8)."

How much of the weight is borne by the compression forces in the intervertebral discs?

Most of it:

In the erect posture, 80 to 90 percent of the axial compressive force is absorbed by the anterior column of the normal spine

Eighty percent of the load transmitted through the lumbar spine passes through the anterior column

Discs connect one vertebral body to another to allow motion of the spine and cushion it against heavy loads. Together, the vertebral bodies and discs bear about 80 percent of the load to the spine.

The anterior cylindrical bodies of the vertebrae, which are spaced apart by intervertebral disks, bear most of the compressive load of the spinal column (approximately 80 percent of the total load).

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.

A 'floating bone' model - like the one on http://biotensegrity.com/images/truss_10.jpg ...that totally ignores the possibility of axial forces in the spine cannot possibly be correct.

Also, that diagram shows the weight bearing ligaments as runing from the spinous prcesses to the transverse processes of the vertebrae below. I have not been able to find any evidence that such ligaments exist. Between vertebrae, there are supraspinous ligaments, interspinous ligaments, and the ligamentum flavum - and various structures around the synovial joints - but none of those run as shown in the diagram.

After discarding axial-force models of the spine, Levin has replaced them with something so grossly inaccurate about how the body is supported as to be totally misleading.

So much for the bones in the spine 'floating'.

What about the idea that other bones float? Since Levin had mentioned the knee as one of the places where the bones didn't touch, I had a look at that joint - and found:

The medial meniscus absorbs up to 55% of the load applied to the medial compartment of the knee and the lateral meniscus bears up to 75% of the lateral compartment load. While walking, forces on the knee increase by 2 to 4 times body weight. These forces can increase by 4 to 8 times when running and jumping.

The meniscus acts as a shock absorber for the knee by spreading compression forces from the femur over a wider area on the tibia.

The medial meniscus bears up to 50% of the load applied to the medial (inside) compartment of the knee.

The lateral meniscus absorbs up to 80% of the load on the lateral (outside) compartment of the knee.

Load-bearing in the knee joint.

Shrive NG, O'Connor JJ, Goodfellow JW.

[...] Confirmatory experimental results show that in partially degenerate human and healthy pigs' knees the menisci bear at least 45 and 75% respectively of the total joint load. The knee joint is similar in this respect to other synovial joints.

Load bearing function:

Menisci distribute forces throughout underlying articular cartilage, thus minimizing point contact;

Menisci bear 40 to 50% of the total load transmitted across joint in extension and 85% of the compressive load is transmitted through the menisci at 90 deg of flexion;

What about Levin's observation that the bones do not touch?

They most certainly do touch - if the knee menisci - pads which carry around half the weight - are removed:

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.

Without the menisci, the forces are no longer distributed over a wide tibial surface area, but over the smaller, limited surface area of femoral tibia.

Loss of medial meniscus causes tibial contact to decrease 55-75% while loss of lateral meniscus decreases contact by 40-45%. This leads to a 200-300% increase in contact pressure and can cause an early onset of degenerative arthritis [...]''

Conclusions

To float in anything like the same way as the struts in Snelson's tensegrities, they would have to not be supported by any compression forces: after all, one does not describe a helium balloon as 'floating' if 10% of its weight is borne by the ground.

In fact, the compression forces supporting the standing body account for the vast majority of the forces holding it up.

The 'floating bone' model is a beautiful theory, spoiled by an ugly fact: nature has no problem using compression forces between bones for support, and does so in practically every joint in the human body.

To suggest that the bones in the spine 'float' - in the face of the evidence that they are supported primarily by compression forces - seems irresponsible to me.

I am concerned that propagating this kind of false anatomical doctrine could - in principle - cause physical problems for people that buy into the delusion - perhaps by causing them to underestimate the compression forces in their spines, possibly leading to ruptured intervertebral discs.

I encourage those involved to seek out other metaphors for how the body supports itself against gravity. If they can find ones which are more accurate, less misleading and contain fewer factual errors, that would help.

Levin suggests he has had some problems getting his ideas accepted. He puts things well:

The column-lever model has been the plush carpet under our feet that we have stood on for hundreds of years. It is difficult to pull the rug out from someone, particularly if there is no floor underneath.

The knee

Discussion

Our discussion is archived here.