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The definition of "fascia" is in flux. Most definitions leave out bone as being part of the fascial system. I argue that bone is ossified fascia and should be thought of as integral to the fascial system.
Bone is Fascia
Stephen M. Levin
Schleip et al’s (2012) What is ‘fascia’? A review of different nomenclatures, as a starting point
and with subsequent posts (Adstrum et al 2016, Stecco et al, 2018), it is clear that nothing
is clear: fascia nomenclature is in a state of flux. The definition of fascia keeps expanding
and what is now considered fascia includes all the muscles except the cells encased within
epimysium and perimysium, the nerve devoid of its neural component, the gut devoid of its
digestive cells, and the organs (kidney, heart, liver, etc.) devoid of their specialized organ
cells. In fact, anything that encapsulates or connects anything to anything else in the body
with the exception of skin, bone, cartilage, the inside of cells, and anything that takes a
compression load, is considered fascia. (It is obscure to me just what the basis is for
excluding the body’s firmer structures). More simply defined, fascia seems to be that which
is not parenchyma (the functional tissue of an organ as distinguished from the connective
and supportive tissue).
Since there is a range of opinions in the medical and scientific community as to how the
term “fascia” should be defined, those of us in the field need to make up our own minds as
our understanding of how tissues in the body functionally interact continues to emerge.
From my perspective as an orthopedic surgeon, manual therapist, and structural theorist,
we might think of the body as a multi-purpose building with supporting walls and structure
and multiple partitions with some of them load-bearing, and others non-load-bearing. Many
of the rooms are crowded with manufacturing processes and some have dual use. The walls
(fascia) give form and continuity to the totality of it all and resists the external entropic
forces pulling it apart. The various apartments and rooms may be filled with stuff
(parenchyma) but without the internal and external fascia walls, there is no structure, no
organ, no function, just a soupy slurry of cells enclosed in a formless leather flask. All
organs are fascial structures that contain and support the specialized cells within them.
Kidney cells are specialized cells within the kidney fascia, neurons are specialized cells
within the neural fascia, etc. It is the fusion of parenchyma and its fascia that define a
tissue, organ, and organ system. These fascial apartments with their occupants fill the
space within the building. Then there is fascia, the building, in which a whole host of
activities and events are transpiring within its many apartments and rooms and that often is
the organizing structure that facilitates the parenchyma’s functionality.
The role of the fascia
It is possible to sub-categorize the fascia into internal systems that primarily concern
themselves with internal functioning of their sub-system and the fascial sub-system that is
mainly concerned with handling the external forces affecting the body and interacting with
the ground.
In the first category, we can place the genitourinary fascia sub-system that encapsulates
the kidneys, ureters, bladder, etc., and joins them into a functional unit. A similar fascial
network exists for the gastrointestinal system, the respiratory system, and so on. In these
systems, although the parenchymal cells may be the soul of the unit, they only function as
they do because of their fascial organization. The fascia is there to support the parenchyma.
In these tissues and organs, the parenchyma are events within the fascia building and are
not intimately involved with the body’s response to external forces. In fact, the body seems
very good at shielding these events from external forces. Breathing, bladder, and bowel
functions continue to the extent that they can because they are partially shielded from
these forces, even under extraordinary stressful conditions.
Then there is the part of the fascial system that deals with external forces head-on. This is
the fascial network that, with its enclosed parenchyma, interacts with the external world, be
it in utero, sea, land, air or space. As examples, we can include the strong fascias such as
the thoracolumbar fascia, the fascia lata, the tendons and ligaments, and also the less
dense peri-muscular fascias and assorted connective tissues. In these, the parenchyma
exists to support the fascia. Most think of this part of the network as the only fascia system,
but, as indicated above, there are others that are integrated with it. They are all connected
but usually have their own specific roles to play, each sub-system of fascia both
independent and interdependent within the entire fascia system.
What about the bone?
Is the bone part of the building’s structural support or just an event within it? To argue that
bone (and cartilage and discs as well) is a specialized organ with its parenchyma as its
primary role, an event separate from the function of the fascia so it should not be included
as a fascia structure, belies the embryologic development of bone and its existence as part
of the fascia network, i.e. its functional role. It is not the case that first osteoblasts exist
and then the fascia room is built around them, but rather that the room is in the process of
construction and the osteoblasts are brought in to plaster the walls. The walls then become
part of the load-bearing structure of the fascia building. Bone is ossified fascia that
incorporates various parenchyma cells within its interstices. Osteoblasts exist within the
interstices of fascia just as muscle cells exist within the interstices of fascia and their very
functional existence is dependent on this fascia structural continuum. Osteoblasts and other
parenchymal cells reside within the walls of this boney apartment but their residence is not
its sole purpose: the walls are there to help hold up the building. Osteoblasts are there to
support fascia; fascia is not there to support the parenchyma (the way fascia is used in the
kidney or liver). If the room is no longer needed, the osteoblasts are evicted, the plaster is
peeled from the walls, and the now non-weight-bearing walls remain as part of the fascial
support network but are used in other ways. Other functions such as hemopoiesis may take
up temporary residence in the apartment and share some space, but those cells may be
structural freeloaders, contributing very little to the building’s structural maintenance.
The continuity
Functional anatomy now describes integrated systems, when in the past we only thought in
terms of independent structures, and the various fascias of the body are now recognized as
part of a “fascial system”. As we move away from thinking of muscles as isolated structures,
we must recognize that muscles are useless unless they pull against something. A functional
support and motor system must include the compression elements such as bones. In a
musculoskeletal system, where does a muscle end and the bone begin? Unless the muscle
cell pulls on fascia, and fascia pulls on bone, nothing much can happen. As Guimberteau
and Delage, (2012), Huijing and Baan (2001), and van der Wal ( 2009), have shown,
boundaries in the body are artificial, arbitrary, descriptive conveniences. Tissues in the body
are not contiguous, just sharing borders, but continuous, transmuting into one another. The
body is an open-office plan, a union of organs united under one roof. The distinction
between the muscle parenchyma and its various -mysiums is a subjective one that is
inconsistent with its function. Where endo-/peri-/epimysium ends and tendon, ligament or
periosteum begins is arbitrary. Like a doorway connecting rooms in an apartment, the
periosteum is continuous with both the fascia of the muscle and the matrix of bone.
If fascia is considered a continuum, and tendons and ligaments are fascia, then to what do
they continue when they transition to bone? The tendon at one end of a muscle is a
continuum of the fascia components of the muscle and continuous with the tendon on the
other end of the muscle. If tendons and ligaments are continuations of the muscle fascia,
then the periosteum (fascia by everyone’s definition) is a continuation (not an attachment
but a continuation) of the tendons, the Sharpey’s fibers are a continuation of the periosteum
and the fibrous matrix of the bone is a continuation of Sharpey’s fibers and out the other
side. The bone’s fascia interpenetrates the bone as the muscle’s fascia interpenetrates
muscle. Bone is not a crystalline column of calcium, it is a stiffly starched shirt very much
dependent on the structure of its fabric for both form and function. The underlying structure
of the bone is the same soft collagenous connective tissue network that composes the rest
of the fascial organ. The calcium crystals manufactured by the bone’s parenchyma do not
become part of the bone’s parenchyma (its inner workings), or a product to be excreted or
used elsewhere in the body; they become part of the fascia support system of the bone
organ. However, the calcium crystals do not dictate the layout of the boney apartment, they
are stiffeners that strengthen the collagenous weight-bearing walls.
Do we define “muscle” as only the parenchyma or do we also include its structural support
system? Remove the parenchyma from a muscle and you have a ligament. It would remain
as part of the fascia continuum that supports the body’s role in contending with external
forces (the thoracolumbar fascia comes close to that description). The role of the muscle
parenchymal cells is to stiffen and tension its fascia; it is the fascia that is the soul of the
parenchyma/fascia interaction. If the interstices and structural functioning of muscle, the
endo-/peri-/epimysium, are to be considered fascia, then why exclude the interstices of
bone from being considered fascia, as the cells within it are specialized for their function as
much as the muscle cells are specialized for theirs?
It is not about stiffness
A distinction by Schleip et al (2012) seems to be that anything that is stiff and resisting
compression is not fascia. This would be at odds with the findings of Davis (1867), Wolff and
Wessinghage (1892), and then Stopak and Harris (1982), who showed that fascia is
transmutable and can manifest as cartilage or bone when under compression and can revert
to its compliant state when the compression is removed. As noted above, the parenchyma
of bone, cartilage, discs, etc. come after the room is built and only when there is a ‘demand’
for the product. As the manufacturing process of the stiffer matter begins, the structure
comes before the contents. Some make the assumption that fascia only pulls. There cannot
be pulling without pushing and isolated areas of fascia may at times stiffen. Skeletal
muscles are hardened and stiffened by their parenchyma interacting with their fascia. And
think of all the soft-bodied creatures and the “muscular hydrostats”, (worms, tongues,
elephants' trunks, tentacles, most penises), where that fascia stiffens without
bones. Biological tissues often have properties that are consistent with “soft
matter” (Gonzales-Rodriquez et al 2012, Gatt et al 2015) rather than the hard matter
physical responses we usually expect of them. For example, many fascial components and
some parenchymal matter may undergo phase changes, often in less than the blink of an
eye. Ice changing to water energy-wise is a big deal, but flowing or stiffening
of biologic matter is a body temperature event that may depend on such things as rate or
force of loading. (For example, see the slow-mo of a boxer being punched, https:// Ossification is only one way
that fascia stiffens, so stiffness should have nothing to do with defining fascia. Stiff or
compliant, the structure remains part of the fascial continuum whose role is to contend with
external forces acting on the body.
What’s in a name?
It is expedient to give different names to regions of the fascia that have different functions;
calling mesentery “mesentery” does not diminish its role as fascia. It is not necessary to
take a hard stand as to what is or is not fascia as the science in the field keeps evolving. As
Schleip et al (2012) and subsequent associated researchers (Adstrum et al 2016, Stecco et
al, 2018) are essentially saying, fascia is what we define it to be. Muscle has muscle cells
within its fascial encasement, bone has osteoblasts and osteoclasts within its fascial
encasement, cartilage has cartilage cells within its fascial encasement, just as pericardium
has heart cells within its fascial encasement, mesentery has digestive cells within its fascial
encasement, the meninges have neural cells within their fascial encasement, and pleura has
lung cells within its fascial encasement. How we define “fascia” is governed by its role
in connecting, encapsulating, and supporting parenchyma, not by its parenchyma’s
What I am suggesting is that the locomotor system, the structure of the body that has most
to do with managing external forces, is a fascial continuum with specialized cells within
certain of its parts and it is the building that encapsulates and physically supports the
other functional components of a body. These specialized cells may be separated into fascial
apartments, but they are linked by the closed kinematic chain network (Levin et al 2017) of
hallways and stairways that unite them into a single structure. This unified structure resists
the external forces that would crush it or tear it apart. The major role of the parenchymal
cells within this fascial complex is to support the fascia in its struggle to resist external
forces. In a kidney or liver, it is the parenchyma that is primal and the fascia facilitates the
space while the parenchyma provides the function. If we are concerning ourselves with the
fascia of the locomotor and structural support system, what holds the body up and gets it
moving, then surely the bone is within that definition: it is just stiffened fascia. Ossified
fascia (bone) is not a non-weight bearing wall in an apartment where there is an event (as
fascia would be in the kidney or liver), but a load-bearing support integral to the structure
of the building. If we are defining a fascial continuum which encapsulates and structurally
supports the cellular components, then the ossified fascia must be included in that
definition. The bone is an organ with its parenchyma having internal obligations but it is
simultaneously an integral component of the fascia support system that is adept at dealing
with external forces. Its dual use does not exclude it from its role as an essential component
of the fascia locomotor and support system.
Acknowledgements: Contributions were made to this paper by Susan Lowell de Solorzano
and Graham Scarr.
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ResearchGate has not been able to resolve any citations for this publication.
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