Connective Tissues: Matrix Composition and Its Relevance to Physical Therapy

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Connective Tissues: Matrix Composition and Its Relevance to Physical Therapy

M Culav, C , and Mervyn J Merrilees  

Key Words: Connective tissues, Fibers, Function, Proteoglycans.

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The purposes of this update are to provide an overview of the composition,

structure, and function of the connective tissue (CT) matrix and to

illustrate how recent research has contributed to an improved understanding

of the ways in which CT responds to mechanical forces. The overview is not

exhaustive, but rather seeks to illustrate the complexity of these tissues,

tissues once regarded as relatively simple structures within a mechanical

system. Specific tissues and their special features, such as those of

cartilage and bone, are not discussed in depth; instead, the overview

emphasizes general principles that apply across the CT spectrum.

Connective tissues and their matrix components have adiversity of roles in

providing for mechanical support, movement, tissue fluid transport, cell

migration, wound healing, and--as is becoming increasingly evident--control

of metabolic processes.

Components of Connective Tissues

Connective tissues and their matrix components make up a large proportion of

the total body mass, are highly specialized, and have a diversity of roles.

They provide for mechanical support, movement, tissue fluid transport, cell

migration, wound healing, and--as is becoming increasingly evident--control

of metabolic processes in other tissues.1,2 Unlike the properties of

epithelial, muscle, or nerve tissues, which depend primarily on their

cellular elements, the properties of CT are determined primarily by the

amount, type, and arrangement of an abundant extracellular matrix (ECM). The

ECM consists of 3 major types of macromolecules--fibers, proteoglycans

(PGs), and glycoproteins--each of which is synthesized and maintained by

cells specific to the tissue type (Fig. 1).

The 2 most important fibrous components of the ECM are collagen and elastin,

both insoluble macromolecular proteins. Collagen has a variety of forms but

is perhaps best exemplified by the prominent aligned fibers of tendons and

ligaments. Other collagen fibers, which are far less prominent, include the

small reticular fibers of soft organs such as the liver and the

submicroscopic fibrils found in basement membranes. The striking feature of

the most prominent collagens is their ability to resist tensile loads.

Generally, they show minimal elongation (less than 10%) under tension; a

proportion of this elongation is not the result of true elongation of

individual fibers, but of the straightening of fibers that are packed in

various 3-dimensional arrays.3,4 In contrast, elastic fibers may increase

their length by 150%, yet still return to their previous configuration.3

The second major component of the ECM is the PGs, a diverse group of soluble

macromolecules that have both structural and metabolic roles.5,6 They

occupy, along with collagen, the interstitial spaces between the cells, form

part of basement membranes, and attach to cell surfaces where they function

as receptors.5,6 Important mechanical functions of PGs include hydration of

the matrix, stabilization of collagen networks, and the ability to resist

compressive forces, an ability best exhibited by the PGs of articular

cartilage.5 Hyaluronan (HA), which is technically not a PG because it lacks

a protein core, is particularly important because it readily en trains large

amounts of water and is abundant in hydrated soft loose tissues where

repeated movement is required (eg, tendon sheaths and bursae).7,8

The third group of matrix molecules, the glycoproteins, are ubiquitous in

all CTs and, as with the PGs, have both structural and metabolic roles.

Their mechanical roles include providing linkage between matrix components

and between cells and matrix components.

An important concept is that the mechanical properties of CT, such as the

ability to resist tension, compression, extensibility, and torsion, are

determined by the proportions of the matrix components. In turn, the

maintenance of these matrix components and their organization depend on the

nature and extent of loading these tissues experience. Generally, tissues

with a high collagen-fiber content and low amounts of PG resist tensile

forces, and those tissues with a high PG content, combined with a network of

collagen fibers, withstand compression (Table 1). Trauma or pathology may

affect normal movements and lead to changed mechanical stresses placed on

the CT. This, in turn, produces changes in the ECM and at the level of gene

expression, as will be discussed below.

Collagens: Framework of the Extracellular Matrix

Nineteen distinct types of collagens are recognized, all with individual

characteristics that serve specific functions in a variety of tissues.9 The

common structural feature that identifies all collagens, however, is a

triple helix region within the molecule. This section of the molecule

provides the characteristic mechanical properties of tendons and ligaments

(ie, the ability to withstand tensile loads).

The triple helix is made up of 3 polypeptide chains folded to form a

ropelike coil. Each chain, known as an -chain, is characterized by repeating

sequences of 3 amino acids, glycine-X-Y (Fig. 2). Because glycine is the

smallest amino acid and occupies the central core of the triple helix, the

repetition of glycine as every third amino acid is essential for the correct

folding of the 3 -chains into the helical conformation.10,11 Specific

collagen types are formed by a variety of -chains and by variations in the

combination of different -chains: in some collagens, all 3 -chains are

identical; in other collagens, 2 -chains may be identical; and in some

collagens, all 3 -chains are different. Alteration of the glycine-X-Y

sequence of amino acids usually results in dysfunction of the collagen

molecule and loss of its mechanical properties (eg, osteogenesis

imperfecta).12 The helical complex, which inherently resists tension, is

further strengthened by intermolecular bonds between the -chains of adjacent

molecules.13

The extremities or terminals of the collagen molecule are nonhelical but are

important for the formation of collagen fibrils and for other nontensile

functions, including interactions with other extracellular components.

The -chains of the principal collagens are synthesized with relatively long

extremities, and, after formation of the triple helix, this newly formed

collagen molecule (called procollagen) is emitted from the cell into the

extracellular space where most of the nonhelical ends are enzymatically

removed. Removal allows the shortened molecules, now called tropocollagen,

to associate with each other and form fibrils, which are visible under the

electron microscope and characterized by distinct cross-bands. These fibrils

then aggregate to form fibers, which are visible under the light microscope,

and bundles of fibers, which are visible to the eye14 (Fig. 3).

Modifications, variations, and additions to the basic triple-helix

conformation give rise to 6 classes of collagens (Tab. 2).9,10 Of most

relevance to physical therapists are the fibril-forming collagens that are

found in tissues (ie, tendons, ligaments) where their primary function is to

resist tensile forces and in tissues where there is a requirement for

resisting tensile loads (ie, dermis, articular cartilage, intervertebral

disks [iVDs], bone). The other 5 classes of collagen, which are much less

abundant but nevertheless essential to CT functions throughout the body,

have a variety of roles.9,10 These classes of collagen and their roles are

summarized in Table 2.

Fibril-forming collagens (types I, II, III, V, and XI). Fibril-forming

collagens account for over 70% of the total collagen found in the body.10

Type I collagen predominates in tissues such as bones, tendons, ligaments,

joint capsules, and the annulus fibrosus of the IVD. Type II collagen is

located principally in articular cartilage and the nucleus pulposus of the

IVD. Type III collagen appears to play a role in the extensibility of tissue

and is found especially in embryonic tissues and in many adult tissues, such

as arteries, skin, and soft organs, where they form reticular fibers.11, 15

The prevalence of type III collagen is also an indicator of tissue maturity

and is also prominent in the initial stages of healing and scar-tissue

formation, where it provides early mechanical strength to the newly

synthesized matrix.14 As fetal development proceeds and as healing tissue

gains in strength, type III fibers are replaced by the stronger type I

fibers.16-18 Generally, type I fibrils have a large diameter, a feature that

correlates with the ability to carry a greater mechanical load. In young,

growing tendons, exercise increases fibril diameter and ultimate tensile

strength, but, in the adult, the effect of exercise is minimal.

Nevertheless, continued tension is necessary to maintain tendon structure

because immobilization leads to a loss of tensile strength.19

Fibrils may also be formed of more than one type of collagen. Types V and XI

combine with type I and II collagen, respectively, to form heterotypic

fibrils, an arrangement that is thought to play a role in determining fibril

diameter and thereby influence mechanical properties. In general, the

greater the fibril diameter, the smaller the percentage of type V and type

XI collagen.11

The tension-resisting property of the fibril-forming collagens is the

principal means of limiting the range of motion of joints, transmitting

forces generated by muscle, imparting tensile strength to the bony skeleton,

and resisting extension by the surface layers of articular cartilage. The

arrangement and alignment of the collagen fibers reflect the mechanical

stresses acting on the tissues.

In tendons, the majority of fibers are aligned in parallel, enabling them to

resist unidirectional forces and to efficiently transmit forces generated by

muscles to bones.4 In comparison, type I fibers in ligaments are often

positioned in slightly less parallel arrays, reflecting the need to resist

multidirectional forces. For example, in ligaments associated with joints,

there is a need to both limit motion and provide for joint stability.

Collagen also plays an important role in attaching tendons and ligaments to

bone. At these junctions, tendons and ligaments usually widen and give way

to fibrocartilage, a transformation where the aligned fibers originating

from the tendon or ligament are separated by other collagen fibers arranged

in a 3-dimensional network surrounding rounded cells.20 This arrangement

helps to transmit tensile forces onto a broad area and reduces the chance of

failure under excessive loading.

The type I collagen fibers of bone have a more complex arrangement.

Generally, the fibrils are arranged in orthogonal arrays, similar to the way

the wood fibers in plywood are arranged in alternating sheets. This

arrangement, especially when configured as small cylinders, such as in

osteons, imparts a great deal of multidirectional tensile strength.

A combination of type I and type II collagen is found in the IVD and in

tendons with fibrocartilaginous pressure pads.21 In the annulus fibrosus of

the IVD, alternating layers of type I fibers link adjacent vertebral bodies

and surround the central nucleus pulposus. The fibrous bands are generally

aligned at angles of about 45 degrees from the vertebral axis, an

arrangement that provides a mechanism for spinal flexibility and for

increasing resistance to excessive motion near the limits of movement. In

the nucleus pulposus, type II collagen predominates and there are high

levels of HA and sulphated PG that function in association with the type II

fibers to provide a hydrated and pressure-resistant core.22

In articular cartilage, the principal collagen fibers are type II, which are

arranged to form a network of bands between the cells. Superficially, these

fibrous bands are mostly tangential to the articular surface, but, with

increasing depth, they become more radial and pass between columns of cells.

Immediately around the cells, other type II collagen fibers combine with

types VI, IX, and XI in a dense capsule arrangement. These fibrous bands

provide both the tensile properties of cartilage and, in conjunction with

large sulphated PG, a mechanism for resisting compression. The capsular

collagen is thought to protect the chondrocytes from these external

forces.23,24

Elastic fibers: extensible elements of the extracellular matrix. Elastic

fibers in the ECM allow tissues such as skin, the lungs, and blood vessels

to withstand repeated stretching and considerable deformation and to return

to a relaxed state. The arrangement of elastin varies and depends largely on

the strength and direction of forces on the tissue. The fibers may be

organized into concentric fenestrated sheets (eg, aorta), as small

individual fibers (eg, skin, lung), or as a 3-dimensional honeycomb-like

network of fine fibers (eg, elastic cartilage).25

Elastic fibers are composed of an elastin core and microfibrils located

mostly around the periphery (Fig. 4). The microfibrils, which are chiefly

made up of fibrillin, initially act as a scaffold on which elastin is

deposited, but once the core elastin is generated, the majority of

microfibrils are displaced to the outer aspect of the fiber. Elastin

contains 2 amino acids (ie, desmosine and isodesmosine) that form

cross-linkages between adjacent tropoelastin chains and are important in

imparting the elastic properties to elastin.26 The exact mechanism of

extensibility is not clearly understood, but the quantity of elastin found

within the tissue usually reflects the amount of mechanical strain imposed

on it and the requirement for reversible deformation (for a review of

elastin see Chadwick and Goode27).

Elastic fibers are widely distributed and found in most organs to varying

degrees. They are found throughout the tracheobronchial tree of the lung and

are largely responsible for accommodating pressure changes.28 The potential

energy stored in the elastic fiber at the end of inspiration is released

during expiration with the consequent assisted recoil of the lung tissue.28

Similarly, the elastin that is found in the walls of arteries withstands the

deformation produced by systole, recoils during diastole, and accommodates

the hemodynamic stresses that the flow of blood imposes on the artery

wall.25, 29

In the dermis, the elastic fibers provide the characteristic resilience of

skin. There is a preferential orientation with coiled fibers aligning

predominantly at right angles to lines of skin tension and in a direction

that allows for greater stretching of the skin.18 Both a changed

conformation and general loss of elastic fibers with increasing age reduce

the ability of the skin to recoil.30

Elastic fibers are relatively sparse in ligaments, with 2 notable

exceptions: the ligamenta nuchae in the cervical region of the vertebral

column and the ligamenta flava connecting the laminae of adjacent

vertebrae.31 The elastic recoil in these ligaments assists in extending the

head, neck, and trunk against gravity, thereby reducing the load imposed on

the erector spinae muscles of the back. The lack of regeneration of

functional elastic fibers in adults is a major problem, and, once this

ability to regenerate is lost, the restoration of normal function is not

possible.30 Elastin, however, is synthesized by adult tissues in response to

cyclic stretching, injury, and ultraviolet radiation32 and by tissues in a

number of disease states, including emphysema.33 Adults, however, apparently

cannot rebuild the elastic fiber assembly mechanisms, and function is not

restored.27 In general, there is a lack of knowledge about the mechanisms of

control of elastic fiber formation.27

Proteoglycans: Hydrators, Stabilizers, and Space Fillers of the

Extracellular Matrix

The PGs are characterized by a core protein covalently attached to one or

more sulphated glycosaminoglycan (GAG) side chains. The core proteins are

generally specific to each of the PG types and show considerable variability

in size. Similarly, there are various GAG chains. The GAG chains are

composed of repeating disaccharide units, with the type and number of units

largely determining the properties of the PG.5 Combinations of sugars make

up the disaccharide units, resulting in 6 major GAGs: chondroitin sulphates

4 (CS A) and 6 (CS C), keratan sulphate (KS), dermatan sulphate (DS, also

known as CS , heparan sulphate, and HA. Hyaluronan is atypical because it

is not attached to a protein core, nor is it sulphated. It is usually

included under a discussion of PG, however, because it is the most abundant

and ubiquitous of the GAGs, and it plays an important role in bonding to

other PGs to form supramolecular complexes.

All GAGs are negatively charged and have a propensity to attract ions,

creating an osmotic imbalance that results in the PG-GAG absorbing water

from surrounding areas. This absorption helps maintain the hydration of the

matrix; the degree of hydration depends on the number of GAG chains and on

the restriction placed on PG swelling by the surrounding collagen fibers.6

The percentage of GAG within CT varies directly with mechanical load.

Tissues subjected to high compressive forces (eg, articular cartilage) have

a large PG content (approximately 8%-10% of the dry weight of the tissue).

Conversely, in tension-resisting tissues such as tendons and ligaments, PGs

are found in relatively small concentrations (approximately 0.2% of dry

weight).7 Furthermore, the proportions of PG species differ with the

mechanical load in such a way that the CS:DS ratio is higher in tissues

subjected to compression and lower in tissues that resist tension.7

Proteoglycan can be divided into aggregating and nonaggregating PGs. The key

features that distinguish between these 2 groups are their ability or

inability to aggregate with HA and the number of GAG side chains that bond

to the protein core.5

Aggregating proteoglycans. Aggregating PGs bond to HA. A large complex

results when many PG monomers link to a single strand of HA. The PG-HA

linkage is stabilized by a glycoprotein known as link protein that helps

secure the PG monomers to the HA.34 Because the GAG chains attached to the

PG core are negatively charged and extend from the core protein like the

bristles of a bottle brush, a high charge density is created. This charge

density induces an osmotic swelling pressure, resulting in the movement of

water into the matrix. Therefore, the PG will tend to swell, but the

tension-resistant collagen fibers and the bonding of the negatively charged

GAG chains to regions of positive charge on collagen fibrils limits the

expansion of PGs to approximately20% of their swelling capacity.35,36 This

limited expansion provides the rigidity of the matrix and, where PG content

is high, endows the tissue with the ability to resist compressive forces.

Two examples of aggregating PGs are aggrecan and versican.

Aggrecan is the best-known and best-understood aggregating PG. It is the

predominant PG in articular cartilage and plays a major role in normal joint

function and in skeletal growth.6, 37 A large compliment of CS chains

(approximately 100) and a smaller compliment of KS chains (approximately 30)

are attached to the protein core of the monomer (Fig. 5). Versican has fewer

CS chains (approximately 30) attached to its core protein, but it also

aggregates with HA and contributes to resistance of compressive forces.5

Versican is found in many tissues, including blood vessel walls,36 the

IVD,22 and some tendon sites that are subjected to compressive loading.21

Versican, along with HA, also functions as an antiadhesive molecule and

facilitates cell migration.38,39

Nonaggregating proteoglycans. The nonaggregating PGs do not bond to HA and

frequently possess only a small number of GAG side chains composed of CS and

DS. They appear to play a limited role in withstanding compression, but they

interact with other matrix components and contribute to mechanical stability

through interaction with collagen. Decorin, which has one GAG chain, is one

of the smallest PGs and functions, in part, to link adjacent collagen

fibrils. The core proteins bind at specific sites on the surface of fibrils,

and the GAG chain extends to form an antiparallel array with a neighboring

decorin GAG chain extending from an adjacent fibril.40 Biglycan (2 GAG

chains) is also small and is found in the matrix between bundles of collagen

fibrils. The mechanical and other functions of biglycan are not understood,

but both biglycan and decorin play a role in regulating cell activity, most

notably through the binding of growth factors through specific high- and

low-affinity sites on the core proteins41 (Fig. 6).

The heparan sulphate PG, syndecan, is attached to the cell membrane and

plays a role in cell growth through binding growth factors, such as basic

fibroblast growth factor, and acting as a co-receptor.42,43 Perlecan is

found close to cell surfaces and contributes to the structure of basement

membranes. In addition to providing support, it assists in cellular

differentiation.44

Hyaluronan is an important component of the aggrecan complex, but it also

exists as a free molecule. Hyaluronan avidly entrains water and is prominent

where the matrix is highly hydrated, such as in loose CT.7,8 A relatively

rich solution of HA is found in the vitreous humor of the eye, the umbilical

cord, and the synovial fluid of joints where its rheological properties are

suited for lubrication.45,46

Role of mechanical forces in determining proteoglycan content and type.

There is good evidence to show that the maintanence of normal tissue

architecture requires normal physiological mechanical loading and that CTs

respond to changes in applied stresses by altering their PG content and

type.

Joint motion is important for the normal maintenance and turnover of PG in

healthy articular cartilage. Conversely, joint immobilization or disuse

results in atrophy of the articular cartilage because of a loss of PG from

the matrix.37 Importantly, this PG loss following joint immobilization is

reversible with a remobilization program.37, 47

Movement alone, without weight bearing, is sufficient to maintain PG content

in sheep articular cartilage.48 The absence of both weight bearing and

movement, however, resulted in a large loss (40%) of PG over a period of 1

month.

Arthritic diseases induced by trauma or degenerative processes also lead to

a disturbance in aggrecan synthesis and degradation and in the inability of

the aggrecan monomer to bond to HA and form large aggregates.49 As a result,

cartilage may fail to resist compression effectively.

The load-bearing IVD also has a high PG content, with the PG being

concentrated mostly in the nucleus pulposus and decreasing peripherally

toward the annulus fibrosus, where the tissue is under increasing tension.

Even the outer region of the annulus fibrosus, however, has a higher PG

content than major tension-resisting structures such as tendons and

ligaments, reflecting the need to resist both tension and pressure. Failure

of the IVD may result, in part, from the inability of the aggrecan and HA to

form a stable complex because of the fragmentation of the link protein.50

In flexor tendons that are angulated around a bony prominence, the outer

portion of the tendon subjected to tension has a low PG content, with a high

proportion of dermatan sulphate PG.7 In contrast, the deeper part of the

tendon that is compressed against the bony surface has a high PG content,

with a high proportion of chondroitin sulphate PG.7, 51 Cell morphology also

changes.51 In the region under tension, the cells are greatly elongated. In

the pressure region, they are rounded and similar to fibrocartilage cells.

Importantly, the removal of the compressive forces by translocation of the

tendon results in rapid (within 2 weeks) remodeling and loss of chondroitin

sulphate PG from the pressure-bearing region. With the application of

tension, total PG content decreases, but with a rise in the proportion of

dermatan sulphate PG. The return of the tendon to its original position

results in a slow (months) increase in PG content.7

More recently, it has been shown that lateral compression of fetal tendons

leads to marked changes in specific PGs and at the level of the gene.52

Aggrecan and biglycan messenger ribonucleic acids (mRNAs) were increased

without a change in decorin or type I collagen mRNAs. Furthermore, these

changes appeared to be driven by increased synthesis of a specific growth

factor (ie, transforming growth factor beta) that is known to be a potent

stimulator for aggrecan and biglycan synthesis but not decorin.52

Glycoproteins: Stabilizers and Linkers of the Extracellular Matrix

Glycoproteins constitute a small, but important, proportion of the total

matrix components. They are soluble, multidomain, multifunctional

macromolecules. Although they do not have prominent mechanical functions,

they are integral to stabilizing the surrounding matrix and linking the

matrix to the cell.53 They are credited with the regulation of many

functions, including producing changes in cell shape, enhancing cell

motility, and stimulating cell proliferation and differentiation.53 Among

the best-characterized glycoproteins are fibronectin, tenascin, laminin,

link protein, thrombospondin, osteopontin, and fibromodulin. Fibronectin is

widespread in the ECM of most CTs and plays a role in cell attachment to

matrix components through, for example, integrin receptors; tenascin, also

involved in modulating cell attachment, is widespread in embryonic tissues

and in certain adult tissues including the myotendinous junction; and

laminin contributes to basement membrane structure.53-57 Link protein, as

discussed above, is required to stabilize the PG aggregates in the cartilage

matrix, fibromodulin interacts with various matrix components and controls

collagen fibril formation, osteopontin sequesters calcium and promotes

tissue calcification, and thrombospondin plays a role in cell attachment.34,

53

Changes to the Matrix in Connective Tissue Diseases and Injury

Under normal physiological conditions, the maintenance of fibers, PG, and

glycoproteins is tightly regulated and controlled through a balance between

synthesis and degradation. This balance is maintained largely by stimulatory

cytokines and growth factors in addition to the degradative matrix

metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases

(TIMPs).58 The synthesis and secretion of MMPs and TIMPs is similarly

modulated by an intricate network of signaling factors, cytokines, growth

factors, and hormones.58

The alteration of the balance between synthesis and degradation influences

normal tissue architecture, impairs organ function, and changes the

mechanical properties of the tissues. As a general observation, net

degradation of matrix components occurs in osteoarthritis, rheumatoid

arthritis, pulmonary emphysema, and osteoporosis. Net increases in synthesis

over degradation leads to accumulation of ECM in fibrotic conditions, such

as interstitial pulmonary fibrosis, liver fibrosis, and the sclerodermas.

Trauma to CT also alters function. A partial or complete rupture of CT

through excessive tensile loading commonly occurs in ligaments and tendons

and at musculotendinous junctions. As a general principle, the loss of

tensile loading, or compressive loading in the case of articular cartilage

in a joint,48 leads to rapid tissue deterioration.59 The repair and

remodeling of these structures is usually slow, taking many months, but

follows a generally predicable pattern.26, 59 During the initial stages of

healing, rupture sites are bridged by newly synthesized type III collagen,

but, as remodeling proceeds, increasing amounts of type I collagen

predominate and provide greater strength.20

Physical exercise also appears to have a beneficial effect on the strength

of normal tendons and ligaments, although the results are somewhat

equivocal. This may be because normal tendons and ligaments are in an

optimal state.60

Tension exerted on wounds is also thought to stimulate collagen synthesis

and enhance the repair process by causing the collagen fibrils to align

parallel to the direction of force sooner than for wounds that are not

subjected to tension.18 The degree of tension exerted on healing skin

wounds, however, is more problematic, as prolonged tension leads to

hypertrophic scarring where excess sulphated PGs produce a thickened

dermis.61,62

Summary

In the last 2 decades, the understanding of CT structure and function has

increased enormously. It is now clear that the cells of the various CTs

synthesize a variety of ECM components that act not only to underpin the

specific biomechanical and functional properties of tissues, but also to

regulate a variety of cellular functions. Importantly for the physical

therapist, and as discussed above, CTs are responsive to changes in the

mechanical environment, both naturally occurring and applied.

The relative proportions of collagens and PGs largely determine the

mechanical properties of CTs. The relationship between the fibril-forming

collagens and PG concentration is reciprocal. Connective tissues designed to

resist high tensile forces are high in collagen and low in total PG content

(mostly dermatan sulphate PGs), whereas CTs subjected to compressive forces

have a greater PG content (mostly chondroitin sulphate PGs). Hyaluronan has

multiple roles and not only provides tissue hydration and facilitatation of

gliding and sliding movements but also forms an integral component of large

PG aggregates in pressure-resisting tissues. The smaller glycoproteins help

to stabilize and link collagens and PGs to the cell surface. The result is a

complex interacting network of matrix molecules5, 10, 53 (Fig. 7), which

determines both the mechanical properties and the metabolic responses of

tissues.

Patients with CT problems affecting movement are frequently examined and

treated by physical therapists. A knowledge of the CT matrix composition and

its relationship to the biomechanical properties of these tissues,

particularly the predictable responses to changing mechanical forces, offers

an opportunity to provide a rational basis for treatments. The complexity of

the interplay among the components, however, requires that further research

be undertaken to determine more precisely the effects of treatments on the

structure and function of CTs.

Acknowledgment

We thank Mr Arthur Ellis, Department of Anatomy With Radiology, School of

Medicine, The University of Auckland, for assistance with preparation of the

figures.

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------------------------------------------------------------------------

© 1999 by the American Physical Therapy Association.

Author Information

EM Culav, MHSc(Hons), BPT, is Senior Lecturer, School of Physiotherapy,

Faculty of Health Studies, Auckland Institute of Technology, Private Bag

92006, Auckland 1020, New Zealand (elizabeth.culav@...). Address all

correspondence to Ms Culav.

CH , MHSc(Hons), BSc, Dip Phys, is Senior Lecturer, School of

Physiotherapy, Faculty of Health Studies, Auckland Institute of Technology.

MJ Merrilees, PhD, is Associate Professor, Department of Anatomy With

Radiology, School of Medicine, The University of Auckland, Auckland, New

Zealand.

------------------------------------------------------------------------

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[Guest guest]

Hi all. Now I am on this list, I want to air a question that I always

wondered about, and since we are finding similarities with things we seem to

have thought were somehow just our own strange bodies, perhaps this rings a

bell as well.

And maybe it's been discussed already when I wasn't on the list....

Does anyone else have bruising of the feet with little or no trauma at all

- trauma like a carpet knot in the wrong spot of the foot, etc., especially

when the feet are warm such as after a bath or in the summer. And I don't

mean a bruise appearing, but the sensation that the whole foot is bruising

from the inside out, generally centered on the balls or heel. I just sit and

watch it happen - immediate swelling, redness, and then the HUGE bruise

starts to appear - incredibly painful, and hard to explain to a doctor

without some very strange looks. I can be walking along and then just stop

when I feel that peculiar umistakable sensation at the beginning, and I

swear and think about all the things I was going to do that day but won't be

able to (it's like predicting the future - strange when I'm walking with a

friend and making plans and then suddenly cancel them!), then find the

fastest way home to some ice which gives some relief from the immediate

pain. Other parts of the body will sometimes have this happen but usually

with more obvious trauma - my whole leg bruised when I fell off my

motorcycle and dislocated my kneecap (my first and last dislocation).

Also, this doesn't seem to fit with the Classic type. Am I right about

that?

Any comments are appreciated. Thanks!

Lenore Hietkamp, Canadian in Seattle