THE STRUCTURE AND FUNCTION
WITH PARTICULAR REFERENCE
OF SYNOVIAL JOINTS,
TO THE MECHANISM OF THEIR LUBRICATION
by
MICHAEL STAFFORD PIPER
M.D.,
University
of B r i t i s h
Columbia,
1968
A THESIS SUBMITTED IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE
i n the Department
of
Anatomy
We a c c e p t t h i s
required
t h e s i s as c o n f i r m i n g t o the
standard
THE UNIVERSITY OF BRITISH COLUMBIA
JUNE,
1972
In p r e s e n t i n g t h i s
thesis
an advanced degree at
the L i b r a r y
I
in p a r t i a l
the U n i v e r s i t y
s h a l l make i t
freely
f u l f i l m e n t o f the
of B r i t i s h
available
for
requirements
Columbia, I agree
for
that
r e f e r e n c e and s t u d y .
f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f
this
thesis
f o r s c h o l a r l y purposes may be granted by the Head o f my Department o r
by h i s
of
this
representatives.
It
thesis for financial
i s understood that copying o r p u b l i c a t i o n
gain s h a l l
written permission.
Department o f
The U n i v e r s i t y o f B r i t i s h
Vancouver 8, Canada
Colui
not be allowed without my
(ii)
ABSTRACT
The
years.
s t r u c t u r e and p h y s i o l o g y
o f s y n o v i a l j o i n t s has been s t u d i e d f o r
Recent advances i n t e c h n o l o g y and i n v e s t i g a t i v e t o o l s have enabled
workers t o g r e a t l y e l u c i d a t e the n a t u r e o f these remarkably
joints.
This
t h e s i s p r e s e n t s a review o f the l i t e r a t u r e d e a l i n g w i t h the
morphology and p h y s i o l o g y
of d i a r t h r o d i a l joints.
development and the gross s t r u c t u r e
c a r t i l a g e and s y n o v i a l membrane.
f l u i d are presented.
the b i o c h e m i s t r y
As
In a d d i t i o n ,
features
of a r t i c u l a r
some o f the f e a t u r e s o f
The r e s u l t s o f r e c e n t
investigation into
and m e t a b o l i s m o f a r t i c u l a r c a r t i l a g e a r e d i s c u s s e d .
the main f u n c t i o n o f s y n o v i a l j o i n t s i s t o p r o v i d e p a i n l e s s ,
t r o l l e d motion, much i n t e r e s t has r e c e n t l y
lubrication
i n these j o i n t s .
nature of j o i n t
l u b r i c a t i o n i s presented,
This
forces
c o n c e r n i n g the
and a t h e o r y o f l u b r i c a t i o n
i s proposed.
t h e o r y was developed from the r e s u l t s o f a t e c h n i q u e o f
synovianalysis
conducted on a s e r i e s o f 61 samples o f s y n o v i a l
samples were c o l l e c t e d from a s e r i e s o f h o s p i t a l p a t i e n t s .
of p a t i e n t s
suffered
comprised o f p a t i e n t s
rheumatoid
The
fluid.
One group
from rheumatoid a r t h r i t i s , w h i l e a second group was
s u f f e r i n g from c o n d i t i o n s
not associated
with
arthritis.
samples were s u b j e c t e d
electrodes,
measured.
con-
f o c u s e d on the mechanism o f
A review o f the l i t e r a t u r e
enhancement by e l e c t r i c a l r e p u l s i v e
The
The e m b r y o l o g i c a l
o f these j o i n t s i s p r e s e n t e d as i s a
d i s c u s s i o n o f the l i g h t and e l e c t r o n m i c r o s c o p i c
synovial
functional
to analysis using
and the c o n c e n t r a t i o n s
In a d d i t i o n ,
i n the s y n o v i a l
fluid
cation sensitive
of i o n i z e d sodium and potassium were
sodium and p o t a s s i u m c o n c e n t r a t i o n s
samples u s i n g
glass
a spectrophotometer.
were measured
(iii)
As
fluid
a result
samples
significantly
It
synovial
fluid
part,
investigations,
from p a t i e n t s
lower
i s concluded
electrical
in
of these
concentration
that
the
of rheumatoid
repulsive
with
forces
rheumatoid
found
arthritis
of i o n i z e d
lower
may
acting within
seen
that
the
synovial
contained
a
sodium.
concentration
arthritis
the c a r t i l a g e a t t r i t i o n
i t was
result
synovial
i n this
Sydney
o f sodium
ions
i n a diminution
joints,
and
in
of
explain,
disease.
M.
Professor
Friedman
and
Head
Department
o f Anatomy
University
of B r i t i s h
(Supervisor)
Columbia
(iv)
TABLE OF CONTENTS
THE STRUCTURE AND FUNCTION OF SYNOVIAL JOINTS, WITH PARTICULAR
REFERENCE
TO THEIR MECHANISM OF LUBRICATION.
Page No.
Introduction
Embryology o f S y n o v i a l
1
Joints
Gross Anatomy o f S y n o v i a l
4
Joints
B l o o d and Nerve Supply o f S y n o v i a l
6
Joints
L i g h t and E l e c t r o n M i c r o s c o p y o f S y n o v i a l
Synovial
Membrane and S y n o v i a l
8
Joints
13
Fluid
18
Biochemistry of A r t i c u l a r Cartilage
25
Metabolism of A r t i c u l a r C a r t i l a g e
28
Lubrication of Synovial
30
Conclusion
Bibliography
Joints
"
37
39
(v)
LIST OF TABLES
Page No.
I.
II.
Sex and Age o f E x p e r i m e n t a l
Sample
33
Sodium and P o t a s s i u m I o n C o n c e n t r a t i o n s
i n Synovial Fluid
o f Rheumatoid and Non-Rheumatoid P a t i e n t s Measured w i t h
Glass Electrodes
III.
34
Sodium and P o t a s s i u m C o n c e n t r a t i o n
i n S y n o v i a l F l u i d of
Rheumatoid and Non-Rheumatoid P a t i e n t s Measured w i t h t h e
IV.
V.
Spectrophotometer
35
S y n o v i a l pH i n Rheumatoid and Non-Rheumatoid P a t i e n t s
35
Serum E l e c t r o l y t e s
(by Flame P h o t o m e t r y ) i n Rheumatoid and
Non-Rheumatoid P a t i e n t s
36
(vi)
ACKNOWLEDGEMENT
tion
I would
like
of this
thesis.
surgeons
t o acknowledge
the assistance
I n p a r t i c u l a r I would
like
given
me
t o thank
i n the preparathe
and r a d i o l o g i s t s a t t h e Vancouver G e n e r a l H o s p i t a l
assistance
i n obtaining
synovial
for
h i s technical assistance.
Dr.
S y d n e y M. F r i e d m a n
his
d i r e c t i o n and support.
fluid
samples,
In addition,
f o r the opportunity
orthopaedic
for their
and Dr. G e r f r i e d
appreciation
t o conduct
Gebert
i s expressed t o
t h i s work,
and f o r
THE STRUCTURE AND FUNCTION OF SYNOVIAL JOINTS, WITH PARTICULAR REFERENCE
TO THE MECHANISM OF THEIR
LUBRICATION
X
INTRODUCTION
"The F a b r i c o f the J o i n t s i n the Human Body i s a S u b j e c t so much the
more e n t e r t a i n i n g , as i t must s t r i k e everyone
that considers i t a t t e n t i v e -
l y w i t h an Idea o f f i n e m e c h a n i c a l C o m p o s i t i o n .
Where-ever the M o t i o n o f
one Bone upon a n o t h e r i s r e q u i s i t e , t h e r e we f i n d an e x c e l l e n t
f o r r e n d e r i n g t h a t M o t i o n s a f e and f r e e :
Apparatus
We s e e , f o r I n s t a n c e , t h e
e x t r e m i t y o f one Bone moulded i n t o an o r b i c u l a r C a v i t y , t o r e c e i v e the
Head o f a n o t h e r , i n o r d e r t o a f f o r d i t an e x t e n s i v e P l a y .
Both a r e c o v e r e d
w i t h a smooth e l a s t i c C r u s t , t o p r e v e n t m u t u a l A b r a s i o n ; connected w i t h
s t r o n g L i g a m e n t s , t o p r e v e n t D i s l o c a t i o n ; and e n c l o s e d i n a Bag t h a t c o n t a i n s a p r o p e r F l u i d d e p o s i t e d t h e r e , f o r l u b r i c a t i n g the Two c o n t i g u o u s
Surfaces.
So much i n g e n e r a l . "
thus w r o t e W i l l i a m H u n t e r , i n 1743 i n a r e m a r k a b l e e s s a y ; "Of the
S t r u c t u r e and D i s e a s e s o f A r t i c u l a t i n g C a r t i l a g e s ( 1 ) " . H i s o b s e r v a t i o n s ,
r e c o r d e d over two hundred y e a r s ago, were e x t r e m e l y a c u t e ; i n f a c t , h i s
d e s c r i p t i o n o f t h e b l o o d s u p p l y o f j o i n t s , the " C i r c u l u s
Articuli
V a s c u l o s u s " has p e r s i s t e d t o the p r e s e n t t i m e .
That the s y n o v i a l j o i n t s c o m p r i s e d a unique body t i s s u e
easily
a c c e s s i b l e t o i n v e s t i g a t i o n l e d e a r l y anatomists t o t h e i r study.
Thus,
w i t h t h e i n t r o d u c t i o n o f t h e m i c r o s c o p e , the unique h i s t o l o g i c a l
appear-
ance o f the a r t i c u l a r c a r t i l a g e s was e s t a b l i s h e d , and c a r t i l a g e was known
t o have a h i g h m a t r i x t o c e l l r a t i o ( 2 ) .
Much i n f o r m a t i o n on the n a t u r e o f s y n o v i a l j o i n t s has been accumul a t e d i n r e c e n t y e a r s , and i t i s the purpose o f t h i s paper t o r e v i e w
- 2 these findings.
As an introduction to"these discussions
embryology of synovial j o i n t s .
that of c a v i t a t i o n .
I s h a l l f i r s t review the
One i n t e r e s t i n g aspect of t h i s f i e l d i s
As the limb buds develop as s o l i d mesenchymal pro-
trusions, the concept of c e l l death providing c a v i t i e s at the s i t e
of j o i n t s has been developed.
Teratologists have recently proposed that
much pre-natal pathology r e s u l t s from inappropriate
c e l l death and question
those factors which are active i n the " c o n t r o l l e d c e l l ' death" seen i n j o i n t
formation. ( 3 )
Despite the great v a r i a t i o n i n gross structure of synovial j o i n t s ,
t h e i r general morphology i s b a s i c a l l y s i m i l a r and these features are
discussed.
Recently developed i n j e c t i o n techniques and auto-radiography
have c l a r i f i e d the patterns
with regard
of c i r c u l a t i o n about j o i n t s , p a r t i c u l a r l y
to the osseous c i r c u l a t i o n , and mention of these findings and
some discussion of t h e i r c l i n i c a l s i g n i f i c a n c e w i l l be made. (4)
With regard
to the fine structure of synovial j o i n t s , the introduc-
t i o n of the electron microscope has been of great s i g n i f i c a n c e .
The f i n d -
ings of a number of investigators are included i n t h i s discussion, as
w e l l as conclusions
reference
reached as a r e s u l t of these studies.
i n this regard
Particular
i s made to the u l t r a s t r u e t u r e of the synovial
membrane and implications regarding
the functions of the various
cells
within this structure.
The structure of the matrix of a r t i c u l a r c a r t i l a g e has greatly
limited studies as t o i t s biochemical makeup and metabolism.
However,
the development of new techniques and modification of old ones has, i n
the past two decades, yielded much of this
The
information.
function of synovial j o i n t s , to paraphrase Hunter, i s to provide
- 3 controlled
painless
v i d e d muscles
design
motion
and g r a v i t y
for stability.
o f the limbs.
f o r motion
However,
synovial
joints
that
greatest
source
of controversey
with
a discussion
lubrication;
of
and, as a r e s u l t
lubrication
enhancement
end, n a t u r e has
ligaments
and
i t i s t h e mechanism
has p r o v i d e d
of the various
and
To t h i s
the greatest
i n recent
mechanisms
of research
by m o n o v a l e n t
architectural
of lubrication
interest
years.
This
proposed
conducted
pro-
as w e l l
thesis
as t h e
concludes
to account
this
cations within
year,
in
for this
a
theory
synovial
fluid.
- 4 Embryology of S y n o v i a l J o i n t s
Fore and hind limb buds appear i n the human embryo at four weeks of
age as outgrowths of p r i m i t i v e mesenchyme. (5, 6, 7)
W i t h i n a few days,
a c e n t r a l core of mesenchyme condenses to become what i s termed the
"blastema".
The blastema subsequently becomes f u r t h e r condensed i n t o
c h o n d r i f i c a t i o n centers, one f o r each s k e l e t a l element.
That part of the
blastema which remains f o l l o w i n g segmentation i s c a l l e d the " i n t e r z o n e . "
These are located at the s i t e s o f future j o i n t s , and are continuous w i t h
the perichondrium surrounding the c a r t i l a g i n o u s models of the bones. (8)
At about f i v e and one h a l f weeks (embryo 11-17 mm) the interzone has
f u r t h e r d i f f e r e n t i a t e d i n t o a three layered s t r u c t u r e w i t h two chondrogenic layers sandwiching a loose middle l a y e r . (9)
The chondrogenic
layers
are continuous w i t h the perichondrium of the neighbouring s k e l e t a l segment.
The intermediate layer i s continuous w i t h the adjacent e x t r a - >
blastemal mesenchyme, which has become v a s c u l a r i z e d at t h i s stage and i s
r e f e r r e d to as the " s y n o v i a l mesenchyme", ( s i x and one h a l f weeks - 25 mm).
(6, 8, 9, 10)
At t h i s stage the outer layers of the s y n o v i a l mesenchyme have begun
to d i f f e r e n t i a t e i n t o the fibrous capsule, w h i l e deeper layers are
d i f f e r e n t i a t i n g i n t o s y n o v i a l membrane and the i n t r a capsular s t r u c t u r e s .
(9)
Most authors agree that the s y n o v i a l space begins t o develop at about
the s i x week stage of growth as minute spaces i n the s y n o v i a l mesenchyme
and the loose middle layer of the interzone. These small spaces subsequently coalese to form the j o i n t c a v i t y . (6, 8, 11, 12)
i s some dispute as to how c a v i t a t i o n a c t u a l l y comes about.
However, there
Some f e e l that
c a v i t a t i o n i s an a c t i v e process accomplished by c e l l u l a r p r o l i f e r a t i o n o f .
- 5 the
lining tissue
(9, 13).
Others i n d i c a t e t h a t c a v i t a t i o n i s the r e s u l t
of c e l l death i n t h e i n t e r z o n e under g e n e t i c c o n t r o l . ( 3 , 6, 14)
Recent
w o r k e r s have s u g g e s t e d t h a t i n t r a u t e r i n e movement i s e s s e n t i a l t o the
p r o c e s s o f c a v i t a t i o n . ( 1 1 , 12)
As c a v i t a t i o n p r o c e e d s , the s y n o v i a l
s u r f a c e i s a t f i r s t rough
and
r a g g e d , but towards the end o f the embryonic p e r i o d a smooth i n t i m a l
l i n i n g appears o v e r l y i n g
the v a s c u l a r s u b s y n o v i a l l a y e r .
the j o i n t s have r e a c h e d a d u l t
configuration.
By e l e v e n weeks
- 6 Gross Anatomy of S y n o v i a l
Joints
A j o i n t or a r t i c u l a t i o n i s formed where two
meet one
a n o t h e r . (15,
l a r g e l y d e t e r m i n e d by
i n the
cartilaginous
The
c h a r a c t e r and
their function.
j o i n t s e x i s t as
the
s u r f a c e s of the
bones are
a d i s c of f i b r o c a r t i l a g e .
j o i n t s are
j o i n t s and
surfaces are
another.
the
articular cartilage
b a s a l l a y e r of the
The
"articular
and
Lining
and
diar-
c o n t i g u o u s bony
are not
attached to
one
The
lamella."
are
bound t o one
of a dense c o n n e c t i v e t i s s u e
bones n e a r the
i n n e r s u r f a c e of the
case
f i r m l y bound t o
a n o t h e r by
cuff.
p e r i p h e r y of the
c a p s u l e are
f i b r o u s c a p s u l e and
a r t i c u l a r margins i s a s y n o v i a l membrane.
a
Generally
articular
seen.
t o p r e v e n t e x c e s s i v e or abnormal movements of the
the
by
and
i s white f i b r o c a r t i l a g e .
A v a r i a b l e number of t h i c k e n i n g s i n the
ligaments act
The
i s c a l c i f i e d and
bones of s y n o v i a l a r t i c u l a t i o n s
c a p s u l e i s a t t a c h e d t o the
surface.
connected
i s u s u a l l y h y a l i n e , however, i n the
articular cartilage
fibrous capsule c o n s i s t i n g
and
r e f e r r e d t o as s y n o v i a l or
articular cartilage
the u n d e r l y i n g bone, the
articular
sterno-manubrial
have common c h a r a c t e r i s t i c s .
of membranous bone the
eventually
pubic symphysis.
covered w i t h a r t i c u l a r c a r t i l a g e
The
epiphysis
These j o i n t s a l l o w some degree of m o t i o n ,
A l l o t h e r j o i n t s i n the body are
t h r o d i a l j o i n t s , and
inferior
temporary and
covered w i t h h y a l i n e c a r t i l a g e
seen
Primary
seen where the
found i n the median p l a n e of the body - the
intervertebral
the
cartilaginous.
such they are
are
f i b r o u s as
e p i p h y s e a l p l a t e between the
As
Secondary c a r t i l a g i n o u s
be
syndesmosis of the
be
body
s t r u c t u r e of j o i n t s
Thus, j o i n t s may
S e c o n d l y , j o i n t s may
d i a p h y s i s of g r o w i n g bones.
ossify.
are
17)
s u t u r e s between c r a n i a l bones, or the
tibiofibular joint.
and
16,
or more bones o f the
These
joints.
a t t a c h i n g to
This h i g h l y s p e c i a l i z e d
the
structure
encloses
a potential
amount o f " S y n o v i a "
The
joint
capsule
(the true j o i n t
or "Synovial
cavity
fibrocartilaginous
the
space
may
disc.
periphery,
is a
small
Fluid".
be d i v i d e d , c o m p l e t e l y
articular
at their
space) w i t h i n which
These
discs
or incompletely,
by a
are u s u a l l y attached
but are not covered
with
to
s y n o v i a l mem-
brane.
Synovial
joints
motion permitted
surfaces,
the
i n them.
the muscles
joints'
are further c l a s s i f i e d
This
according
i s determined
t h a t a c t upon the j o i n t ,
e x c u r s i o n by the c a p s u l e
and
to the kind of
by t h e shape
of the
and t h e l i m i t s
ligaments.
articular
placed
on
- 8 B l o o d and Nerve S u p p l y o f S y n o v i a l J o i n t s
I n o r d e r t o u n d e r s t a n d the b l o o d s u p p l y t o s y n o v i a l j o i n t s , one must
c o n s i d e r two s y s t e m s .
The
f i r s t i s the a n a s t o m o t i c network of v e s s e l s
s u r r o u n d i n g and s u p p l y i n g the s o f t t i s s u e s ; t h a t i s the l i g a m e n t s ,
and synovium.
The
second system i s t h a t w h i c h s u p p l i e s the
capsule
epiphyseal
r e g i o n and hence the s u b c h o n d r a l bone.
Generally speaking
the b l o o d s u p p l y t o l o n g bones i n a p a r t i c u l a r
species i s remarkably constant.
A s y s t e m i c v e s s e l u s u a l l y runs p a r a l l e l
t o the l o n g a x i s o f the bone, and g i v e s a n u t r i e n t a r t e r y w h i c h e n t e r s
diaphysis.
the
T r a n s v e r s e l y a r r a n g e d v e s s e l s form a n a s t o m o t i c networks around
the j o i n t s , and a r e the o r i g i n o f v e s s e l s s u p p l y i n g the e p i p h y s e a l
metaphyseal r e g i o n s .
system although
supplying i t .
The venous s y s t e m tends t o p a r a l l e l the
and
arterial
t h e r e a r e u s u a l l y more v e i n s d r a i n i n g a bone t h a n
arteries
T y p i c a l l y a s i n g l e d i a p h y s e a l a r t e r y e n t e r s the n u t r i e n t
foramen and r a m i f y s i n the marrow c a v i t y .
O c c a s i o n a l l y there are
two
n u t r i e n t a r t e r i e s , as i n the human femur ( 1 , 1 5 ) .
The
e p i p h y s e s and d i a p h y s e s
smaller nutrient a r t e r i e s .
for
the m e t a p h y s i s and one
a l l y d e s c r i b e d by H u n t e r .
A r t i c u l i V a s c u l o s i a s " , and
o f l o n g bones a r e s u p p l i e d by numerous
These r a m i f y i n t o two a n a s t o m o t i c s y s t e m s ,
f o r the e p i p h y s i s .
one
These systems were o r i g i n -
He r e f e r r e d t o the c h a n n e l s as "The
Circulus
l i k e n e d them t o the v e s s e l s o f the m e s e n t e r y .
The m e t a p h y s e a l v e s s e l s can be s e e n t o a r i s e d i r e c t l y f r o m the
circulus
a r t i c u l i v a s c u l o s u s , w h i l e the e p i p h y s e a l v e s s e l s a r i s e from v a s c u l a r
a r c a d e s l y i n g on the n o n - a r t i c u l a r p a r t o f the e p i p h y s i s . (4)
I t has
been
p o s t u l a t e d t h a t t h i s d i f f e r e n t o r i g i n o f e p i p h y s e a l and m e t a p h y s e a l a r t e r i e s
may
(18)
account f o r the d i f f e r e n c e i n b l o o d p r e s s u r e
found i n the two
systems.
- 9The b l o o d s u p p l y o f the m e t a p h y s i s changes between f o e t a l and a d u l t
life.
(19j 20, 21)
I n the f o e t u s ,
the metaphysis
n u t r i e n t a r t e r y a l o n e , w h i l e i n the a d u l t ,
the p e r i p h e r a l two f i f t h s
the m e t a p h y s e a l a r t e r i e s
of the m e t a p h y s i s ,
b e i n g s u p p l i e d by the n u t r i e n t a r t e r y .
i s s u p p l i e d by the
supply
the c e n t r a l t h r e e f i f t h s
This s i t u a t i o n e x i s t s
(22)
still
i n the
" g r o w i n g end" of l o n g bones.
I n the " n o n - g r o w i n g e n d " e v e n t u a l l y a l l b l o o d
derives
arteries.
from the m e t a p h y s e a l
L i k e w i s e t h e r e i s a change i n the b l o o d s u p p l y of e p i p h y s e s .
infant,
(up t o one y e a r ) ,
metaphyseal v e s s e l s
p i e r c e the
In
the
cartilaginous
e p i p h y s e a l p l a t e and thus s u p p l y the b a s a l p a r t of the e p i p h y s i s .
After
one y e a r of age the e p i p h y s e a l p l a t e becomes i m p e r v i o u s t o t h e s e metaphyseal vessels,
and i s s u p p l i e d s o l e l y by the e p i p h y s e a l v e s s e l s .
Thus i t can be seen t h a t
l o n g bones,
the b l o o d s u p p l y o f the e p i p h y s e a l p a r t
and hence t h e s u b c h o n d r a l r e g i o n i s of v a r i a b l e
depending upon the age of the bone and the s i t e
be of r e l e v a n c e
of s t u d y .
T h i s f a c t may
of
the
(19)
The r o l e of the s u b c h o n d r a l e p i p h y s e a l v e s s e l s
a r t i c u l a r c a r t i l a g e w i l l be d i s c u s s e d l a t e r ,
of the e p i p h y s i s now deserves
i n the n u t r i t i o n of
however,
the v a s c u l a r
anatomy
mention.
Many e p i p h y s e a l n u t r i e n t a r t e r i e s
arise
from the c i r c u l u s a r t i c u l i
and anastomose w i t h i n the e p i p h y s e s
immature s k e l e t o n some branches
of l o n g bones.
In
the
pass d i r e c t l y to the s u b c h o n d r a l a r e a
the c a r t i l a g i n o u s growth . p l a t e ( e p i p h y s e a l p l a t e ) ,
epiphyseal arteries
of
origin,
i n c o n s i d e r i n g the e t i o l o g y of a v a s c u l a r n e c r o s i s
c a p i t a l femoral e p i p h y s i s .
vasculasis
(23)
but the m a j o r i t y of
pass towards the a r t i c u l a r and n o n - a r t i c u l a r
of
the
surfaces
of the e p i p h y s i s .
As t h e s e e p i p h y s e a l n u t r i e n t a r t e r i e s
e p i p h y s i s a d j a c e n t t o the m e t a p h y s i s
pass from t h a t p a r t of
towards the a r t i c u l a r s u r f a c e ,
the
they
- 10 f e e d i n t o a number o f a r t e r i a l arcades w h i c h s u b s e q u e n t l y
f u r t h e r r a d i a t i n g a r t e r i e s . (15)
give r i s e
to
T h i s p a t t e r n of the a r t e r i a l s u p p l y
of
the e p i p h y s i s i s s i m i l a r t o the p a t t e r n o f the v a s c u l a r s u p p l y seen i n
the c a r t i l a g i n o u s e p i p h y s e a l p r e c u r s o r . (24)
The a n a l o g y between a v a s -
c u l a r n e c r o s i s o f the f e m o r a l head i n a d u l t s (25) and t h a t seen f o l l o w i n g
r e d u c t i o n o f a c o n g e n i t a l l y d i s l o c a t e d h i p (26) i s e a s i l y s e e n .
I t has been n o t e d t h a t the d i s t r i b u t i o n o f e p i p h y s e a l a r t e r i e s i s not
r e l a t e d t o the t r a b e c u l a r a r c h i t e c t u r e o f the bone. (27)
t h e t r a b e c u l a e i s known t o be v a r i a b l e depending upon the
f o r c e s o p e r a t i v e i n v a r i o u s c o n d i t i o n s . (28)
e p i p h y s e a l a r t e r i e s appears r e m a r k a b l y
The
The p a t t e r n o f
biomechanical
However, the d i s t r i b u t i o n o f
constant.
terminal epiphyseal a r t e r i o l e s which
emanate
from the
anasto-
m o t i c a r c a d e s i n the c e n t r a l p a r t of t h e e p i p h y s i s r a d i a t e towards the
s u b c h o n d r a l bony p l a t e w h i c h s u p p o r t s
the c a r t i l a g e .
Here they
s i n u s o i d a l loops a b u t i n g a g a i n s t the b a s a l c a r t i l a g e l a y e r s .
form
These a r e
s i m p l e s i n u s o i d s not a t a l l l i k e the d i l a t e d , v a r i c o s e s i n u s e s seen on
the m e t a p h y s i a l
s i d e o f the growth p l a t e . (23)
O c c a s i o n a l l y these
sub-
c h o n d r a l loops can be seen t o r e a c h i n t o the c a l c i f i e d zone o f c a r t i l a g e ,
but o n l y v e r y r a r e l y i n t o the more s u p e r f i c i a l zones o f u n c a l c i f i e d
cartilage.
The
(4)
s i n u s o i d a l network i n the immediate s u b c h o n d r a l a r e a o f the
e p i p h y s i s tends t o be p a r a l l e l t o the a r t i c u l a r c a r t i l a g e .
anastomosis i s s e p a r a t e d
This v a s c u l a r
from the most b a s a l l a y e r o f the c a r t i l a g e
c a l c i f i e d zone o f c a r t i l a g e ) by a t h i n p l a t e o f bone.
As has been men-
t i o n e d t h i s bony p l a t e i s o c c a s i o n a l l y seen t o be p e r f o r a t e d by
v a s c u l a r c h a n n e l s w h i c h e x t e n d i n t o the c a l c i f i e d zone of the
cartilage.
(the
small
articular
T h i s f i n d i n g l e n d s c r e d e n c e t o the s u g g e s t i o n t h a t the
a r t i c u l a r c a r t i l a g e d e r i v e s a t l e a s t p a r t o f i t s n u t r i t i o n from the
sub-
«»
c h o n d r a l c i r c u l a t i o n . (29)
discussed
The n u t r i t i o n o f a r t i c u l a r c a r t i l a g e w i l l be
i n more d e t a i l s u b s e q u e n t l y .
The v e i n s d r a i n i n g t h e s i n u s e s w i t h i n t h e e p i p h y s e s , a l t h o u g h h a v i n g
a r a d i a t e p a t t e r n s i m i l a r t o t h e a r t e r i e s , do n o t accompany t h e a r t e r i e s .
They tend t o be more numerous t h a n t h e a r t e r i e s and d r a i n t o t h e c i r c u l u s
a r t i c u l i vasculosis.
J o i n t s have a b a s i c p a t t e r n o f n e r v e s u p p l y .
The branches t o them
a r i s e , e i t h e r d i r e c t l y o r i n d i r e c t l y , from the nerves which supply the
o v e r l y i n g s k i n and t h e muscles w h i c h move t h e j o i n t .
l a r nerve supplies a f a i r l y
joint.
Each major a r t i c u -
l a r g e and r e l a t i v e l y c o n s t a n t p o r t i o n o f t h e
There a r e r e g i o n a l d i f f e r e n c e s , i n t h a t c e r t a i n p a r t s o f each
j o i n t a r e more h e a v i l y s u p p l i e d w i t h n e r v e f i b e r s t h a n a r e o t h e r
regions.
These p a r t s a r e u s u a l l y t h o s e most s u b j e c t t o d e f o r m a t i o n d u r i n g movement
o f t h e j o i n t and t h e g r e a t e r number o f f i b e r s have a g r e a t e r
concentration
of p r o p r i o c e p t i v e endings. (30)
A r t i c u l a r n e r v e s have a common b a s i c p a t t e r n , and c o n t a i n b o t h
m y e l i n a t e d and n o n - m y e l i n a t e d f i b e r s .
A l l myelinated f i b e r s are afferent
u s u a l l y c a r r y i n g i m p u l s e s from endings o f t h e R u f f i n i t y p e .
corpuscles
are a l s o seen, u s u a l l y i n the f i b r o u s capsule.
Pacinian
Some o f t h e
s m a l l e r a f f e r e n t m y e l i n a t e d f i b e r s end i n s i m p l e o r f r e e nerve e n d i n g s i n
the c a p s u l e and a r e f e l t t o be s i m p l e p a i n
receptors.
Many p f t h e n o n - m y e l i n a t e d f i b e r s a r e p o s t g a n g l i o n i c
fibers supplying
sympathetic
t h e smooth muscle o f t h e a r t i c u l a r v e s s e l s .
Some n o n -
m y e l i n a t e d f i b e r s end i n f r e e n e r v e endings and c a r r y a f f e r e n t p a i n
impulses.
The m a j o r i t y o f b o t h m y e l i n a t e d and n o n - m y e l i n a t e d f i b e r s a r e
found i n t h e f i b r o u s c a p s u l e , .the s y n o v i a l membrane i t s e l f b e i n g v e r y
p o o r l y s u p p l i e d w i t h p a i n f i b e r s . (31)
Many o f
the
fibers
These supply
the
blood
brane,
and
thereby
temperature
of
evidence
the
One
That
one
overlying
lead
joints.
to
of
of
failure
i n the
of
flow
of
the
are
capsule
through
the
and
supply
innervated
nerve.
procedures
This
vasomotor
fibrous
joints
nerve
a joint
articular
nerves
skin i n distended
common s u p p l y
characteristic
other
vessels
c o n t r o l blood
i s , each r e g i o n
least
may
of
the
in articular
joint.
to
The
pathological
by
to
synovial
one
of
nerve
elevated
joints
is
(32)
joints
is
overlap.
is supplied
overlapping
denervate
vasosensory.
s y n o v i a l mem-
overlying skin.
pattern
designed
and
and
by
at
innervation
painful
arthritic
- 13 L i g h t and E l e c t r o n M i c r o s c o p y o f A r t i c u l a r C a r t i l a g e
In r o u t i n e h i s t o l o g i c a l preparations o f a r t i c u l a r c a r t i l a g e s
d r o c y t e s a r e seen t o l i e i n l a c u n a e d i s t r i b u t e d
i n t r a c e l l u l a r m a t r i x . (33)
young c a r t i l a g e .
chon-
w i t h i n an abundant h y a l i n e
The c h o n d r o c y t e s a r e s p a r c e , even i n v e r y
(34, 35)
E a r l y m i c r o s c o p i s t s d e f i n e d f o u r d i s t i n c t zones i n a d u l t a r t i c u l a r
c a r t i l a g e , and d e s c r i b e d d i f f e r e n c e s i n t h e s p a t i a l arrangement as w e l l as
the c e l l u l a r morphology i n these z o n e s . (34)
Zone I , t h e s u p e r f i c i a l o r t a n g e n t i a l s t r a t u m c o n s i s t s o f f l a t t e n e d
or markedly ovoid c e l l s l y i n g adjacent
t o the s u r f a c e w i t h the long a x i s o f
the c e l l s p a r a l l e l t o t h e a r t i c u l a r m a r g i n .
T h i s a r e a has a l s o been
r e f e r r e d t o as t h e " g l i d i n g zone". (36)
I n Zone I I , t h e i n t e r m e d i a t e o r t r a n s i t i o n a l s t r a t u m ,
a r e plump and o v a l and d i s t r i b u t e d
the chondrocytes
i n a random f a s h i o n .
Zone I I I i s r e f e r r e d t o as t h e deep o r r a d i a t e s t r a t u m .
i n t h i s zone tend t o be s m a l l and r o u n d .
The c e l l s
They a r e a r r a n g e d i n s h o r t ,
i r r e g u l a r columns p e r p e n d i c u l a r t o t h e a r t i c u l a r s u r f a c e .
The
b a s a l l a y e r o r Zone I V i s the c a l c i f i e d s t r a t u m , and l i e s
t o t h e s u b c h o n d r a l bony p l a t e .
and
irregular with pyknotic
On h e m a t o x y l i n
adjacent
I n t h i s a r e a t h e c e l l s tend t o be s m a l l
nuclei.
and e o s i n s t a i n t h e c a l c i f i e d s t r a t u m i s s e p a r a t e d
from t h e more s u p e r f i c i a l l a y e r s by a t h i n wavy b l u e l i n e .
The n a t u r e o f
t h i s b a s o p h i l i c a r e a i s unknown; i t has been c a l l e d t h e " t i d e m a r k " .
mention w i l l be made o f t h e v a r i a t i o n s
Further
found i n t h e c h o n d r o c y t e s o f d i f f e r -
ent zones, p a r t i c u l a r l y w i t h r e g a r d t o s t u d i e s w i t h t h e e l e c t r o n m i c r o s c o p e .
M e n t i o n s h o u l d be made now, however, o f t h e l i g h t m i c r o s c o p i c
of t h e i n t r a c e l l u l a r m a t r i x o f a r t i c u l a r
cartilage.
appearance
- 14 I t has
been known f o r many y e a r s t h a t c a r t i l a g e c o n t a i n s
f i b e r s imbedded w i t h i n the ground s u b s t a n c e and
responsible
at l e a s t p a r t i a l l y
f o r the s t i f f n e s s of the m a t r i x . (37)
suggested that c o l l a g e n
Benninghoff, i n
formed bundles a r r a n g e d i n a r c a d e s .
t h e s e b u n d l e s were anchored i n the c a l c i f i e d s t r a t u m and
towards the s u r f a c e
collagen
t h r o u g h the r a d i a t e s t r a t u m .
ran
He
1925,
felt
that
vertically
At the t r a n s i t i o n a l zone
the f i b e r s t u r n e d o b l i q u e l y t o f o l l o w the t a n g e n t i a l o r i e n t a t i o n of
superficial layer.
They t h e n t u r n e d down, r u n n i n g p e r p e n d i c u l a r l y
t h r o u g h the r a d i a l zone t o become anchored a g a i n i n the c a l c i f i e d
These " B e n n i n g h o f f a r c a d e s " can be demonstrated u s i n g phase
m i c r o s c o p y . (30)
back
zone.
contrast
However, r e c e n t e l e c t r o n m i c r o s c o p i c s t u d i e s have i n d i -
c a t e d a f a r more random o r i e n t a t i o n of the
The
the
e l e c t r o n m i c r o s c o p e has
fibers.
r e c e n t l y been used e x t e n s i v e l y
a t t e m p t t o c l a r i f y the n a t u r e of a r t i c u l a r c a r t i l a g e .
i n an
These s t u d i e s
shed l i g h t on the o r g a n i z a t i o n o f the e x t r a c e l l u l a r m a t r i x , as w e l l
i n d i c a t i n g the s o u r c e of the components of the m a t r i x .
studies with
greater
indicated a v a r i a t i o n
i n the s i z e of the f i b e r s found w i t h i n the m a t r i x , and
c o n f i r m e d t h i s . (40, 41, 42, 43)
to a
o f the " g l i d i n g c a r t i l a g e s " .
E a r l y s t u d i e s w i t h the e l e c t r o n m i c r o s c o p e (39)
has
as
In a d d i t i o n ,
the s c a n n i n g e l e c t r o n m i c r o s c o p e have c o n t r i b u t e d
u n d e r s t a n d i n g o f the n a t u r e o f the s u r f a c e
have
subsequent work
I n t r a c e l l u l a r d i f f e r e n c e s are
also
n o t e d i n the s p e c i f i c zones o f the c a r t i l a g e .
E l e c t r o n m i c r o g r a p h s of the s u p e r f i c i a l or t a n g e n t i a l s t r a t u m show i t
t o e x t e n d t o a depth of 200
t o 600
m i c r a , b e i n g t h i c k e r a t the
of the c a r t i l a g e where i t b l e n d s w i t h
the p e r i c h o n d r i u m .
the c a r t i l a g e i s c o v e r e d w i t h a l a y e r of f i n e f i b e r s and
three micra i n depth.
The
periphery
surface
filaments
of
about
S c a n n i n g e l e c t r o n m i c r o g r a p h s of t h i s s u r f a c e
layer
- 15 have
l e d some i n v e s t i g a t o r s
adsorbed
this
hyaluronic
concept.
layer
show
as
the
acid.
(45)
to believe
(44)
Light
microscopists referred
"lamina splendens".
elements
o f the
the
typical
collagen
periodicity
surfaces
and
are
arranged
at oblique or
are
tightly
the
deeper
packed w i t h
layers.
fine
In
remainder
angles
relatively
the narrow
t o one
little
zones
region
seen
r u n n i n g between c o l l a g e n - b u n d l e s .
The
of
the
reticulum,
flattened
secretory
the
layers.
vacuoles
filamentous f i b r i l s
In
These
than
fibers
those
their
and
a r e randomly
seen
larger
cell
64 OA*
of
more a b u n d a n t ,
The
of
i n the
and
containing
superficial
chondrocytes
membrane n o t
results
arranged
from
seen
fine
and
material
matrix.
classic
and
have
zone.
fibers
less
The
and
fine
I.
rough
those
endo-
apparatus
collagen
of
fibers
to
600A" a r e
tendency
to form
cell
of
to
0
ground
a scalloped
the
from
A number
(41)
I t i s suggested
to
appearance.
seen.
bundles
are
appearance
that
wall
with
substance
filamentous f i b r i l s
i n Zone
with
of
i n appearance
amorphous
zone have
merging
are
markedly
(47)
300
cells
100X
beaded
developed
fibers
compared
a number
similar
r a n g i n g from
of
the G o l g i
of material.
i n this
large vesicles
also
poorly
small,
stratum)
a diameter
articular
m a t r i x as
a characteristic
the e x t r a c e l l u l a r
a g a i n the
are
of
individual
a periodicity
a relatively
Zone I I , ( t h e t r a n s i t i o n a l
a periodicity
ance
are seen
t o the
o f Zone I d i f f e r
apparently devoid
a diameter
These
intervening
There
the m i t o c h o n d r i a are
sacs
They have
strata)
of m a t r i x s u r r o u n d i n g the
and
chondrocytes
They have
of
superficial
(tangential
another.
i n diameter w i t h
40A* d i a m e t e r
of
small e l l i p s o i d
deeper
plasmic
forms
fibrils
12OA
to this
running p a r a l l e l
this
filamentous
fibers
layer
have c o r r o b o r a t e d
o f Zone I
o f 64 OX.
i n bundles
right
to a
(46)
fibrous
35 OA
i t corresponds
Biochemical studies
The
about
that
this
is
seen.
to
appear-
to discharge
- 16 their
contents.
endoplasmic
(41)
reticulum,
many v e s i c l e s .
These
The
very
In
findings
producing
s i m i l a r to
of
The
dense
preparation
the
of
calcified
necrotic,
and
separated
matrix.
The
mentioned
healthy
istic
cells
(1),
1743,
and
this
have been
ute
(4)
to
the
good
from
calcified
above,
of
i t was
has
that
deposits
of
the
the
of
the
actively
radiate
strata,
is
a
be
larger
slightly
(41)
i s random
sections
to
there
the
appears
cartilage
s i m i l a r to
c a r t i l a g e matrix
by
appear
matrix.
a narrow
a homogenous
of
Zone I I I ; t h a t
i n immature
nourishment
wall
that
seen.
those
of
organelles.
chondrocytes
involved
with
f i b e r s have
again
are
the
been confirmed
described
zone
of
suggested
the
to
rough
47)
perpendicular
calcified
m a t r i x has
cells
tend
are
of"Zone
for e l e c t r o n microscopy.
cell
those
complex
cells
collagen
they
this
i n the
by
Golgi
42,
Zone I I I ,
in ultra-thin
of
sections
38,
arrangement
extensive
a number
resemble
organelles
In
less
these
(37,
the
f i b e r s running
surrounded
however,
As
Their
z o n e , many
are
Again
chondrocytes
calcium
of
developed
of mitochondria are
that
640A\ b u t
state
of
slightly
number
picture
of w e l l
developed
collagen.
Zone I I .
1
II with
The
the
of
a preponderance
a well
large
p e r i o d i c i t y of
(47)
as
particularly
that
large quantity
t o most w o r k e r s
some o b s e r v e r s
surface.
Zone
a
(400A t o 800S).
diameter
be
well
addition
protein,
is a
electron microscopic
although
to
as
indicate
characteristic
in
There
cells
zone
i n recent
synthesis.
but
chondrocytes.
these
are
or
appearance.
However,
the
the
character-
(47)
aneural
(48)
depths
of u n c a l c i f i e d
i s they have
times.
hinder
calcified wall i s ,
electron-dense
c a r t i l a g e was
the
degenerate
appear n e c r o t i c .
in protein
animals
The
In
IV
and
avascular
Cartilage
felt
They d i s a p p e a r
not
to
early
channels
contribin
life.
- 17 The
one
n u t r i t i o n o f a r t i c u l a r c a r t i l a g e w i l l be d i s c u s s e d l a t e r , however
f u r t h e r note as t o t h e dynamics o f t h e c h o n d r o c y t e s h o u l d be made a t
t h i s time.
A l t h o u g h m i t o t i c f i g u r e s have been d e s c r i b e d i n t h e c a r t i l a g e
o f immature a n i m a l s they a r e n o t seen i n n o r m a l a r t i c u l a r c a r t i l a g e from
mature a n i m a l s . ( 4 1 , 4 2 , 4 7 , 49)
under c o n d i t i o n s
M i t o t i c f i g u r e s a r e o c c a s i o n a l l y seen
o f l a c e r a t i v e i n j u r y (42) o r c o m p r e s s i o n . ( 5 0 )
animals c a r t i l a g e c e l l s w i t h
i r r e g u l a r shaped n u c l e i a r e o c c a s i o n a l l y
and were once thought t o r e p r e s e n t a m i t o t i c d i v i s i o n .
studies with
In older
seen,
In recent years
t r i t i a t e d t h y m i d i n e , ( a n i n d i c a t o r o f DNA r e p l i c a t i o n ) have
shown t h a t a zone o f c h o n d r o c y t e p r o l i f e r a t i o n e x i s t s a d j a c e n t t o t h e zone
o f c a l c i f i c a t i o n u n t i l t h e onset o f m a t u r i t y . (51)
These f i n d i n g s w o u l d tend t o i n d i c a t e t h a t t h e c e l l count o f a r t i c u l a r c a r t i l a g e would d i m i n i s h w i t h a g i n g .
T h i s seems t o be t r u e i n t h e
case o f r a b b i t s and c a t t l e , b u t s t u d i e s w i t h human a r t i c u l a r c a r t i l a g e have
f a i l e d t o show a s i m i l a r f a l l i n c e l l c o u n t . (35)
I n view of the f r e -
quency o f c e l l death seen on e l e c t r o n m i c r o s c o p i c s t u d i e s , these f i n d i n g s
are as y e t u n e x p l a i n e d .
- 18 S y n o v i a l Membrane and S y n o v i a l
The
Fluid
unique n a t u r e o f d i a r t h r o d i a l j o i n t s i s a f u n c t i o n o f b o t h t h e
h y a l i n e c a r t i l a g e found a t t h e a r t i c u l a t i n g ends o f bones, and t h e
s y n o v i a l membrane.
Normal s y n o v i a l membrane c a n be thought o f as c o n -
s i s t i n g o f two p a r t s :
a t h i n i n n e r l i n i n g bounding t h e j o i n t space and
r e f e r r e d t o as t h e s y n o v i a l i n t i m a , and a s u p p o r t i v e
the s u b i n t i m a o r s u b s y n o v i a l
As
discussed
derived
(52).
l a y e r r e f e r r e d t o as
tissue.
i n t h e embryology o f j o i n t s , t h e s y n o v i a l membrane i s
from t h e embryonic mesenchyme o f t h e o r i g i n a l s k e l e t a l b l a s t e m a
The r e g e n e r a t i o n
o f s y n o v i a l membrane f o l l o w i n g t o t a l synovectomy
i n d i c a t e s t h a t i t i s r e a l l y a m o d i f i e d form o f m e s o t h e l i u m . (53)
The
f u n c t i o n o f s y n o v i a l membrane i s f e l t t o be t w o - f o l d .
Certain
c e l l s appear t o have a p h a g o c y t i c f u n c t i o n and t h e s t r u c t u r e i s a l s o
responsible
f o r the production
of synovial f l u i d .
(54)
These phenomena
w i l l be d i s c u s s e d more f u l l y .
Grossly
t h e s y n o v i a l membrane c a n be seen t o l i n e t h e i n n e r
of d i a r t h r o d i a l j o i n t s .
I t i s a t t a c h e d t o t h e margins o f the a r t i c u l a r
c a r t i l a g e s , and t h e s u b i n t i m a b l e n d s w i t h t h e i n t r a - a r t i c u l a r
The
surface
periosteum.
membrane o f t e n may be redundant and thrown i n t o f o l d s or v i l l i .
The
b l o o d s u p p l y o f t h e s y n o v i a l membrane, as w e l l as t h a t o f t h e
fibrous capsule,
derives
from t h e c i r c u l u s a r t i c u l i v a s c u l o s i s .
Generally
s p e a k i n g t h e r e i s an a r t e r i a l network l y i n g j u s t beneath t h e s u b i n t i m a as
i t blends w i t h the contiguous periosteum.
arcades
This gives r i s e t o a r t e r i a l '
w h i c h pass t h r o u g h t h e s y n o v i a l membrane and appear t o b r a n c h i n t o
c a p i l l a r y beds a t t h e j u n c t i o n between i n t i m a and s u b i n t i m a . ( 5 5 , 4)
Under t h e l i g h t m i c r o s c o p e s y n o v i a l membrane c a n be c l a s s i f i e d on
the b a s i s o f t h e predominant s t r u c t u r e o f t h e s u b i n t i m a l c o n n e c t i v e t i s s u e .
Thus, depending upon the site of origin of the synovium i t may be fibrous,
fibro-areolar, areolar, areolar-adipose or adipose. (33, 55)
The synovial
intima has a characteristic appearance composed of a layer of cells
varying in depth from one to four imbedded in a matrix of ground substance.
The intimal cells have frequent branching c e l l processes with a finely
granular cytoplasm which extend to the surface of the synovial membrane and
to other cells.
One of the characteristic features of the synovial intimal
cells is that although they are more numerous on the surface of the
synovial membrane, they do not form a continuous unbroken layer as on an
endothelial surface. (55, 56)
The intimal cells are generally ellipsoid
in shape with an oval nucleus.
The synovial intima lies on a meshwork of subintimal connective tissue,
with numerous capillaries just below the lining surface. (57)
The sub-
intimal portion of the synovial membrane also has a characteristic c e l l
population. About three percent of the subintimal cells are mast cells,
and tend to occupy the region between the intima and subintima. Also within
the subintima is a collection of unclassified connective tissue cells,
predominantly fibroblasts. (56)
Collagen fibers provide the major
structural support for the subintima, and, to a lesser degree, the intima.
Electron microscopy has contributed greatly to the study of the synovial
membrane, both with regard to the nature and function of the synovial cells,
and to the relationship between the cells and the surrounding matrix.. The
light microscopic impression that synovial cells did not form a complete
lining of the joint cavity has been confirmed by electron microscopy. (47, 58)
Thus the subintima is not exposed to the joint space, although intimal cells
and their surrounding matrix are bathed in synovial fluid.
is the absence of a basement membrane in synovial membrane.
Also noticeable
- 20 The
n a t u r e o f the s y n o v i a l i n t i m a l c e l l s has
w i t h the e l e c t r o n m i c r o s c o p e .
and
Two
been g r e a t l y e l u c i d a t e d
types have been d i s t i n g u i s h e d ; types A
B c e l l s ; the A c e l l s b e i n g more f r e q u e n t .
p h o l o g i c a l d i s t i n c t i o n between the two
(58)
The
fundamental mor-
types o f c e l l s i n t h a t type A
c o n t a i n prominent G o l g i complexes and many smooth w a l l e d v a c u o l e s ,
cells
but
l i t t l e rough e n d o p l a s m i c r e t i c u l u m , w h i l e type B c e l l s are r i g h l y endowed
w i t h e n d o p l a s m i c r e t i c u l u m , but G o l g i systems and
are s c a n t y .
B, and
Despite
smooth w a l l e d v a c u o l e s
the f a c t t h a t type A c e l l s are more f r e q u e n t
despite t h e i r morphological
than t y p e
d i f f e r e n c e s , most a u t h o r s t e n d t o agree
t h a t the d i f f e r e n t types do not r e p r e s e n t
d i s t i n c t populations
of
cells,
but r a t h e r v a r i a n t s whose morphology i s dependent upon f u n c t i o n a l a c t i v i t y .
This concept i s s u p p o r t e d by the f a c t t h a t i n t e r m e d i a t e
c e l l types w e l l
endowed w i t h b o t h rough e n d o p l a s m i c r e t i c u l u m and G o l g i complexes are
found.
A l s o , i n some p a t h o l o g i c a l c o n d i t i o n s t h e r e may
one
c e l l t y p e over a n o t h e r .
The
f i n d i n g of two
be a p r o l i f e r a t i o n o f
(47)
types o f c e l l s i n s y n o v i a l i n t i m a has
led to a
g r e a t e r i n s i g h t i n t o the f u n c t i o n o f t h e membrane, and much i n t e r e s t
centered
around the p r o d u c t i o n o f s y n o v i a l f l u i d .
Of p a r t i c u l a r
i s the s o u r c e o f s y n o v i a l mucin or h y a l u r o n i c a c i d .
shown t o produce h y a l u r o n a t e
i n v i t r o and
glucuronic
contributes,
S y n o v i a l membrane has
i n v i v o . (54, 59)
c o l l o i d a l i r o n t e c h n i q u e s w i t h e l e c t r o n m i c r o s c o p y , i t has
h y a l u r o n i c a c i d i s produced i n the G o l g i complex and
m a t r i x and
of
T h i s c o i l e d macromolecule i s
r e s p o n s i b l e f o r the v i s c o u s n a t u r e of s y n o v i a l f l u i d , and
at l e a s t p a r t i a l l y , to j o i n t l u b r i c a t i o n .
interest
This i s a s u l f a t e -
free mucopolysaccharide containing equimolar concentrations
a c i d and N - a c e t y I g l u c o s a m i n e . (54, 56)
has
been
Using
been shown t h a t
transported
the j o i n t c a v i t y by the l a r g e smooth w a l l e d v a c u o l e s .
t o the
I t seems
s i n c e the G o l g i complex and smooth w a l l e d v a c u o l e s are the
characteristic
f e a t u r e s o f t y p e A c e l l s , i t i s t h e s e c e l l s w h i c h are m a i n l y r e s p o n s i b l e
for hyaluronic acid synthesis.
(60)
I n a d d i t i o n t o the p r o d u c t i o n
of h y a l u r o n i c a c i d , the type A
a r e a c t i v e i n removing s u b s t a n c e s from the s y n o v i a l f l u i d .
These c e l l s
a r e a c t i v e i n p h a g o c y t o s i n g b o t h s m a l l p a r t i c u l a t e m a t t e r , and
o b j e c t s such as c e l l fragments and e r y t h r o c y t e s .
The
cells
also larger
(61)
f i n d i n g o f l a r g e amounts o f rough e n d o p l a s m i c r e t i c u l u m i n the
less frequent
type B c e l l s has
i n d i c a t e d t h a t t h e s e c e l l s are
engaged i n the m a n u f a c t u r e o f p r o t e i n .
actively
A l t h o u g h a l m o s t a l l the p r o t e i n
found i n s y n o v i a l f l u i d i s f e l t t o d e r i v e from the plasma, two p e r c e n t o f
t h i s p r o t e i n i s found i n the s y n o v i a l f l u i d f i r m l y bound t o h y a l u r o n i c
a c i d . (56, 62)
I t has
f l u i d p r o t e i n may
been s u g g e s t e d t h a t t h i s s m a l l f r a c t i o n ' o f s y n o v i a l
a r i s e from the s m a l l p o p u l a t i o n o f type B c e l l s . (47, 58)
The m a t r i x of the s y n o v i a l i n t i m a has
varying electron density.
a m o t t l e d appearance, w i t h
C o l l a g e n w i t h c h a r a c t e r i s t i c 640^
i s s e e n , as w e l l as v e r y f i n e f i b r i l l a r y f i b e r s .
periodicity
I n areas o f synovium
where the i n t i m a l c e l l s a r e t h r e e t o f o u r deep, a rough d i v i s i o n between
s u p e r f i c i a l , m i d d l e and
deep zones can be made.
Generally speaking, i t i s
i n the deep zone t h a t most of the banded c o l l a g e n i s found, w h i l e the
finer
f i b e r s are s e e n i n the more s u p e r f i c i a l zones w i t h the g r a n u l a r amorphous
matrix.
The
(47, 58)
electronmicroscopic
appearance of the s u b s y n o v i a l
i n t i m a depends l a r g e l y upon the n a t u r e o f the a r e a
or a d i p o s e ) .
( i . e . fibrous, areolar
I n a l l v a r i e t i e s , f i b r o b l a s t s , mast c e l l s and
phages a r e f o u n d .
One
t i s s u e or s u b -
t i s s u e macro-
c h a r a c t e r i s t i c f e a t u r e o f the s u b i n t i m a
v a s c u l a r i t y , w i t h many a r t e r i o l e s and
capillaries.
The
i s i t s high
capillaries
extend
- 22 i n t o the i n t i m a , and i n f a c t may
be s e p a r a t e d
a t h i n band o f i n t i m a l m a t r i x . (47)
only
There i s a v a r i a b l e amount o f banded
c o l l a g e n p r o v i d i n g the framework o f t h e
Any
from the j o i n t space by
subintima.
d i s c u s s i o n o f the s y n o v i a l membrane must i n c l u d e a c o n s i d e r a t i o n
of s y n o v i a l f l u i d .
16th c e n t u r y , who
The
t e r m " s y n o v i a " was
f i r s t used by P a r a c e l s u s i n the
l i k e n e d i t s appearance t o egg w h i t e . (56, 62)
Synovial
f l u i d has been d e f i n e d as " a p r o t e i n c o n t a i n i n g d i a l y s a t e o f b l o o d p l a s m a ,
t o w h i c h m u c i n , s e c r e t e d by the s y n o v i a l c e l l s ,
w a t e r d i f f u s e s through
t h e s y n o v i a l t i s s u e spaces i n t o the l a r g e r
s p a c e , the j o i n t c a v i t y " . (62)
t o 7.8.
tissue
Grossly, s y n o v i a l f l u i d i s c l e a r , pale
y e l l o w , v i s c i d , and does not c l o t .
f r o m 7.39
i s added as t h e plasma
I t i s w e a k l y a l k a l i n e , w i t h a pH
of
(63)
The c h a r a c t e r i s t i c v i s c o s i t y o f s y n o v i a l f l u i d i s p r o v i d e d by
u r o n i c a c i d , a s u l f a t e - f r e e mucopolysaccharide.
polymerized molecule of equimolar
N-acetylglucosamine
This i s a long
chained
p r o p o r t i o n s of g l u c u r o n i c a c i d
h a v i n g a m o l e c u l a r w e i g h t o f about one
hyal-
and
million.
H y a l u r o n i c a c i d c o n t e n t i n normal s y n o v i a l f l u i d i s a p p r o x i m a t e l y
3.6
milli-
grams p e r gram. (17)
V a r i o u s f u n c t i o n s f o r h y a l u r o n i c a c i d i n s y n o v i a l f l u i d have been p r o posed.
I t i s operative i n maintaining lubrication i n j o i n t s .
T h i s can
be
s e e n when h y a l u r o n i d a s e i s i n t r o d u c e d i n t o a j o i n t and r a p i d breakdown o f
a r t i c u l a r c a r t i l a g e r e s u l t s . (64, 65)
h y a l u r o n a t e a c i d may
joint.
i n some way
I t has a l s o been suggested' t h a t the
m a i n t a i n the w a t e r b a l a n c e w i t h i n
the
(56)
Normal s y n o v i a l f l u i d c o n t a i n s about one
t h i r d the p r o t e i n found i n
serum (2.5 grams p e r 100 m i l l i l i t r e s ) , w i t h a h i g h e r a l b u m i n - g l o b u l i n
ratio.
A l b u m i n forms 75 p e r c e n t o f the p r o t e i n .
The p e r c e n t a g e o f a l p h a
- 23 and b e t a g l o b u l i n i s s i m i l a r t o t h a t found i n serum, w h i l e t h e p e r c e n t a g e
of
a l p h a - 2 g l o b u l i n and gamma g l o b u l i n i s l e s s .
F u r t h e r m o r e , a l l serum
p r o t e i n s w i t h a m o l e c u l a r w e i g h t i n excess o f 160,000 a r e e x c l u d e d
synovial joints.
from
Of p a r t i c u l a r i m p o r t a n c e i s the absence o f f i b r i n o g e n ,
p r o t h r o m b i n , t h r o m b i n , and t h r o m b o p l a s t i n .
These l a r g e m o l e c u l a r w e i g h t
p r o t e i n s are e x c l u d e d from j o i n t s by the p r e f e r e n t i a l p e r m e a b i l i t y o f the
c a p i l l a r y membrane and the ground s u b s t a n c e o f the s y n o v i a l membrane. (17)
Thus s y n o v i a l f l u i d w i l l not
clot.
S y n o v i a l f l u i d n o r m a l l y c o n t a i n s a s m a l l c e l l u l a r component, r a n g i n g
up t o 200 w h i t e c e l l s per m i l l i l i t r e .
The m a j o r i t y o f the n u c l e a t e d c e l l s
w i t h i n s y n o v i a l f l u i d a r e p h a g o c y t e s , w i t h monocytes b e i n g the most p r e valent.
The normal low p o p u l a t i o n o f p o l y m o r p h o n u c l e a r
l e u k o c y t e s (about
2 p e r c e n t ) l e a d s t o the s u s p i c i o n o f i n f e c t i o n when any h i g h e r l e v e l i s
f o u n d . (66)
Red b l o o d c e l l s are v e r y r a r e i n normal f l u i d and a r e f e l t t o
r e s u l t from trauma.
I n o r g a n i c m a t e r i a l s such as n o n - p r o t e i n n i t r o g e n
and g l u c o s e t e n d t o
r e f l e c t serum l e v e l s , b o t h b e i n g s l i g h t l y lower i n s y n o v i a l f l u i d .
Similar-
l y , e l e c t r o l y t e s t e n d t o be s l i g h t l y lower i n s y n o v i a l f l u i d t h a n t h e serum,
(62) and a f u r t h e r d i s c u s s i o n o f the c o n c e n t r a t i o n s o f sodium and
will
potassium
follow.
A number o f enzymes have been found i n s y n o v i a l f l u i d , and c o n s i d e r a b l e
e f f o r t i s p r e s e n t l y b e i n g expended i n an a t t e m p t t o c o r r e l a t e abnormal
enzyme l e v e l s w i t h a r t i c u l a r c a r t i l a g e damage i n v a r i o u s j o i n t d i s e a s e s .
A number o f dehydrogenases,
t r a n s a m i n a s e s and phosphotases
have been
measured i n s y n o v i a l f l u i d , however t h e i r l e v e l o f a c t i v i t y seems t o c o r r e l a t e w i t h t h e number of l e u k o c y t e s found i n the s y n o v i a l
One
fluid.
o f the f e a t u r e s o f s y n o v i a l f l u i d i s i t s tendency t o
accumulate
- 24 as a r e s u l t of pathology.
Synovianalysis i s a great aid i n diagnosing
various forms of a r t h r i t i s and i n assessing the e f f i c a c y of treatment. (66)
- 25 Biochemistry
of
Articular
Cartilage
F u n c t i o n being so c l o s e l y
recently
In
been expended i n t o
addition,
new
metabolism of
high matrix
The
to
light
lar
matrix
ing
features
have
chondrocyte,
cell
structure,
the
much e f f o r t
biochemical nature
enabled researchers
in
spite
of
to
limitations
microscopic
Biochemically,
one
of
cartilage
hyperhydrated
state,
m e a s u r i n g up
to
80%.
(as
a
mineral
but
polysaccharides.
articular
tein
507o
content
tical
It
cartilage
Over
with
of
is
that
cult
to
separate
saccharide.
is
has
This
Much o f
to
largely
dependent
of
of hydroxylysine.
appears
to
of
the
the
chains
of
although
the
the
intracellu-
most
the
is
not
cartilage
has
content
tightly
bound,
b e i n g bound t o
elastic
there
interest-
the water
combination with
It
( 7 0 )
to
of
the
the
muco-
behaviour
content.
and
may be a
( 6 9 )
of
907,
of
to
the
be
from the
a complex i n t e r a c t i o n
chondroitin sulfates
and
iden-
slightly
proved extremely
cartilage
pro-
diffi-
protein
between
polythe
collagen
( 7 1 )
component o f
molecular weight
attached
i m p o s e d by
c o m p o s i t i o n appears
articular
b e due
of
content
in
articular
collagens,
The p r o t e i n p o l y s a c c h a r i d e s
organic
cartilage.
the
upon the w a t e r
The a m i n o a c i d
collagen
water
the water
been suggested that
other
the
this
form a g e l
dry weight
mucopolysaccharide side
fibrils.
felt
collagen.
increased quantity
its
proportion of
is
the
of
is
( 6 7 , 68)
large
crystal)
of
determine
characteristics
been d e s c r i b e d .
i n bone,
has
ratio.
and e l e c t r o n
have
to
clarifying
techniques
the
related
side
core varies
the
cartilages.
macromolecules,
a number o f
protein
articular
make up
chains
consisting
of
considerably
sulfated
in
i
size
majority
These
of
of
the
complexes
a protein
rest
are
core
polysaccharides.
and amino a c i d
of
the
high
to which
is
Although
content,
the
- 26 b a s i c u n i t i s thought t o be about 4000S 1 ong w i t h about 60
s i d e c h a i n s . (72,
The
polysaccharide
73)
p o l y s a c c h a r i d e s i d e c h a i n s a r e composed o f r e p e a t e d
"glycosaminoglycan"
(GAG)
units.
Three o f these d i m e r i c u n i t s have been
described i n a r t i c u l a r c a r t i l a g e ; chondroitin-4 s u l f a t e ,
s u l f a t e , and k e r a t i n s u l f a t e . (73)
macromolecule may
The
range between 50 and
The p r o t e i n p o l y s a c c h a r i d e s
dimeric
chondroitin-6
number o f s a c c h a r i d e u n i t s i n a
50,000.
are n o t d i f f u s e l y d i s t r i b u t e d
c a r t i l a g e , but a r e found i n h i g h e s t c o n c e n t r a t i o n i m m e d i a t e l y
t h e c e l l s . (74)
I n a d d i t i o n the t h r e e g l y c o s a m i n o g l y c a n s
d i s t r i b u t e d w i t h i n the c a r t i l a g e .
throughout
surrounding
are
differently
As mentioned i n the d i s c u s s i o n o f the
u l t r a s t r u c t u r e o f c a r t i l a g e , the c o n c e n t r a t i o n o f c e l l p r o t e i n p o l y s a c c h a r i d e s i s markedly d e c r e a s e d i n the s u p e r f i c i a l or g l i d i n g s t r a t a .
(40)
K e r a t i n s u l f a t e i s found p r i m a r i l y i n the i n t e r t e r r i t o r i a l r e g i o n s
i s between the v a r i o u s s t r a t a ) .
c o n c e n t r a t i o n s but may
(that
O t h e r w i s e , k e r a t i n s u l f a t e i s i n low
be found t o i n c r e a s e w i t h o l d age.
Chondroitin-6
s u l f a t e i s t h e most p r e v a l e n t of the t h r e e glycosaminogens found i n
a r t i c u l a r c a r t i l a g e , w i t h chondroitin-4 s u l f a t e having a high concentration
i n the embryonic p e r i o d but d e c r e a s i n g w i t h a d v a n c i n g age.
The
p r o t e i n p o l y s a c c h a r i d e s a r e f e l t t o be i m p o r t a n t
(75)
i n providing
much o f the r e s i l i e n c y o f a r t i c u l a r c a r t i l a g e - perhaps by m a i n t a i n i n g
the
s p a t i a l o r i e n t a t i o n o f the c o l l a g e n f i b e r s .
Some o t h e r o r g a n i c m a t e r i a l s are found i n s m a l l q u a n t i t i e s i n a r t i c ular cartilage.
S i a l i c a c i d , probably
i n the form of s i a l o p r o t e i n ,
likely
e x i s t s i n c o m b i n a t i o n w i t h the p r o t e i n p o l y s a c c h a r i d e complexes. (76)
In
a d d i t i o n t h e r e a r e low c o n c e n t r a t i o n s of l i p i d s
of
c a r t i l a g e . (77)
The n a t u r e and
found w i t h i n the m a t r i x
f u n c t i o n of t h i s m a t e r i a l i s unknown.
Also,
a number
these w i l l
With
o f enzymes
be d i s c u s s e d
regard
concentration
of
and unbound
in
the
i s similar
(68, 7 8 ) , w i t h
sulfates
concentration of sulfated
the c o n c e n t r a t i o n
polyanionic
found w i t h i n
under the metabolism of
of electrolytes
fluids
the
been
t o t h e i n o r g a n i c components
cellular
bound
have
two
serves
cartilage.
found
First,
i n other
the
as
Also,
the
intra-
concentration
(understandably
polysaccharides).
o f sodium, w h i c h
matrix.
to that
high,
cartilages;
of a r t i c u l a r cartilage,
exceptions.
are very
the a r t i c u l a r
there
the p r i n c i p a l
i n view
i s an
of
increase
cation for
- 28 Metabolism of A r t i c u l a r C a r t i l a g e
U n t i l f a i r l y r e c e n t l y , measurements o f r e s p i r a t o r y a c t i v i t y had i n d i c a t e d t h a t a r t i c u l a r c a r t i l a g e had a v e r y low m e t a b o l i c
activity.
How-
e v e r , subsequent s t u d i e s p o i n t e d out the v e r y low c e l l mass o f c a r t i l a g e ,
and
s u g g e s t e d t h a t the r a t e o f m e t a b o l i c
of other t i s s u e s .
Most of the g l y c o l y t i c enzymes have been demonstrated
i n a r t i c u l a r c a r t i l a g e , and
only minimally
a c t i v i t y per c e l l approached t h a t
i n a d d i t i o n , c a r t i l a g e has
a f f e c t e d by p e r i o d s o f oxygen d e p r i v a t i o n .
l a c t i c a c i d has
In a d d i t i o n ,
been found i n h i g h c o n c e n t r a t i o n i n the t i s s u e .
f i n d i n g s have s u g g e s t e d t h a t the m e t a b o l i c
tent with i t s avascular
developed.
been shown t o be
c h a r a c t e r , and
These
a c t i v i t y of c a r t i l a g e i s c o n s i s -
t h a t the a n a e r o b i c pathway i s w e l l
(79)
I n a d d i t i o n , e a r l y i n v e s t i g a t o r s a l s o thought t h a t the
were " i n e r t " and
at m a t u r i t y , had
l i t t l e synthetic a c t i v i t y .
chondrocytes
However,
subsequent i n v e s t i g a t i o n s u t i l i z i n g r a d i o s u l f a t e uptake showed a r a p i d r a t e
of turnover
f o r a t l e a s t the s u l f a t e d p o l y s a c c h a r i d e
m a t r i x . (80)
I t appears now
component of
the
t h a t the c h o n d r o c y t e s a r e i n v o l v e d i n a
" c o n t i n u a l complex p a t t e r n o f a c t i v i t y d i r e c t e d e n t i r e l y ( o r a l m o s t
e n t i r e l y ) t o s y n t h e s i s , maintenance and
degradation
t h a t compose the i n t r a c e l l u l a r m a t e r i a l " . (81)
o f the macromolecules
I t has
been shown t h a t
the
c h o n d r o c y t e i s c a p a b l e o f the s y n t h e s i s o f the p r o t e i n o f both the p r o t e i n
polysaccharide
and
c o l l a g e n , the s y n t h e s i s o f the p o l y s a c c h a r i d e
p o l y m e r i z a t i o n ) , and
the s u l f a t i o n o f the p o l y s a c c h a r i d e .
(82, 83)
o f the q u a l i t a t i v e and q u a n t i t a t i v e i n f o r m a t i o n on the m e t a b o l i c
o f a r t i c u l a r c a r t i l a g e has
been d e r i v e d from the use
s p e c i f i c t o the macromolecules s y n t h e s i z e d .
degradation
r a t e s can be d e t e r m i n e d .
(and i t s
Much
activity
of i s o t o p i c t r a c e r s
Thus both s y n t h e s i s
and
From these s t u d i e s a number o f
con-
- 29 e l u s i o n s have been r e a c h e d .
The
r a t e o f s y n t h e s i s o f the macromolecules
has been found t o be more r a p i d i n immature a n i m a l s but a f t e r an
d e c l i n e remains f a i r l y c o n s t a n t
throughout l i f e .
(49)
A number o f
a n t i m e t a b o l i t e s can be seen t o i n h i b i t t h i s s y n t h e s i s .
n e t s y n t h e s i s o f macromolocules has
initial
I n a d d i t i o n , the
been shown t o i n c r e a s e i m m e d i a t e l y
following lacerative injury to a r t i c u l a r c a r t i l a g e .
increase i n synthesis i n o s t e o a r t h r i t i c j o i n t s .
A l s o , t h e r e i s an
(84)
Normal c a r t i l a g e shows no n e t g a i n i n m a t r i x volume, d e s p i t e the
r a t e of s y n t h e s i s of i t s c o n s t i t u e n t macromolecules.
t i v e s y s t e m has
R e c e n t l y , a degrada-
been d e s c r i b e d c a p a b l e o f s p l i t t i n g the p r o t e i n p o l y -
s a c c h a r i d e a t o r n e a r t h e s u g a r - p r o t e i n band s i t e .
been r e f e r r e d t o as " c a t h e p s i n - D " , a l y s o s o m a l
One
such p r o t e a s e
has
enzyme found b o t h i n t r a
and
I t has been p r o p o s e d t h a t t h e c a p a c i t y of b o t h r a t e s o f s y n t h e s i s
and
e x t r a c e l l u l a r l y . (85,
86)
degradation s u g g e s t s the p r e s e n c e of an a c t i v e i n t e r n a l r e m o d e l l i n g
(81,
high
system.
86).
That the c h o n d r o c y t e s o f a r t i c u l a r c a r t i l a g e a r e m e t a b o l i c a l l y a c t i v e
r a t h e r t h a n i n e r t has become o b v i o u s .
However, c o n t r o v e r s y s t i l l
as t o the s o u r c e o f n u t r i t i v e m a t e r i a l s f o r t h i s a c t i v i t y .
exists
Most e a r l y
i n v e s t i g a t o r s , n o t i n g the a v a s c u l a r i t y o f the t i s s u e , s u g g e s t e d t h a t
s y n o v i a l f l u i d was
the o n l y s o u r c e o f n u t r i t i o n f o r c a r t i l a g e .
the
Although
m i c r o v a s c u l a r c h a n n e l s have been demonstrated p e r f o r a t i n g the bony p l a t e
and e n t e r i n g the p o o r l y c a l c i f i e d b a s a l zone o f immature c a r t i l a g e
c h a n n e l s cannot be i d e n t i f i e d i n mature a n i m a l s .
(40, 87)
Most c u r r e n t
i n v e s t i g a t o r s f e e l t h a t n u t r i t i v e m a t e r i a l s d i f f u s e t h r o u g h the
from the s y n o v i a l f l u i d b a t h i n g the c a r t i l a g e s u r f a c e .
these
matrix
- 30 Lubrication of Synovial
Joints
As H u n t e r n o t e d i n 1743, the prime f u n c t i o n o f s y n o v i a l j o i n t s i s t o
" r e n d e r m o t i o n s a f e and f r e e " and t h a t t h i s f u n c t i o n was a c c o m p l i s h e d by a
"bag
that contains
a proper f l u i d deposited there
contiguous s u r f a c e s " .
(1)
f o r l u b r i c a t i n g t h e two
This p a r t i c u l a r l y f r i c t i o n - f r e e movement, found
t o have a c o e f f i c i e n t o f f r i c t i o n o f about 0.013, (88) has f a s c i n a t e d b o t h
e n g i n e e r s and b i o l o g i s t s f o r y e a r s , and t h e s o u r c e o f t h i s
efficient lubrication i s s t i l l highly controversial.
extremely
The h i g h l y
viscous
n a t u r e o f s y n o v i a l f l u i d has been n o t e d , and has been f e l t t o add g r e a t l y
t o t h e l u b r i c a t i o n o f s y n o v i a l j o i n t s . ( 8 9 , 90)
A number o f t h e o r i e s have been proposed i n an a t t e m p t t o e x p l a i n t h e
phenomenon o f j o i n t l u b r i c a t i o n .
"Hydrodynamic l u b r i c a t i o n " was s u g g e s t e d
when t h e i n c o n g r u i t y o f j o i n t s u r f a c e s was n o t e d . (91)
two
r i g i d surfaces
In this
system,
s e t a t an a n g l e t o one a n o t h e r were seen t o produce a
wedge-shaped gap. When one s u r f a c e moves t a n g e n t i a l l y t o t h e o t h e r t h e
viscous
s y n o v i a l f l u i d i s drawn i n t o t h e d i m i n i s h i n g gap, and a p r e s s u r e
i s developed w i t h i n the f l u i d s u f f i c i e n t t o support the v e r t i c a l l o a d .
p r o p o s a l was a t t a c k e d
on t h e b a s i s
This
t h a t hydrodynamic l u b r i c a t i o n i s n o t
s u i t e d t o r e c i p r o c a t i n g movement, as seen i n p h y s i o l o g i c a l c o n d i t i o n s . (88)
A l s o , the high pressures to which a r t i c u l a t i n g j o i n t s are subjected
t o i n normal w e i g h t b e a r i n g
l e d t o the development o f t h e t h e o r y o f
"boundary l u b r i c a t i o n " as a p p l i e d t o s y n o v i a l j o i n t s .
I n t h i s model, t h e
l u b r i c a n t ( f o r example t h e h y a l u r o n a t e o f s y n o v i a l f l u i d ) has an
for
the s o l i d s u r f a c e s .
affinity
Movement t a k e s p l a c e between mono-molecular l a y e r s
of adherent l u b r i c a n t . (88)
T h i s model i s t h e o r e t i c a l l y a t t r a c t i v e , how-
e v e r i n v i t r o e x p e r i m e n t s have found t h i s f o r m o f l u b r i c a t i o n a c t i n g a t
o n l y v e r y l i g h t l o a d s . (92) •
- 31 The
t h e o r y o f "weeping l u b r i c a t i o n " r e l a t e d
to t h e l u b r i c a t i o n mechanism. (93)
the n u t r i t i o n of c a r t i l a g e
The porous n a t u r e
of a r t i c u l a r
age e n a b l e s i t t o t a k e up l u b r i c a t i n g f l u i d ; w i t h t h e a p p l i c a t i o n
load the f l u i d
i s squeezed out and p r o v i d e s a f l u i d
cartil-
of a
film for lubrication.
( 9 3 , 94)
Most i n v e s t i g a t o r s
f e e l that "elastohydrodynamic l u b r i c a t i o n " i s a c t i v e
i n p e r i o d s o f r a p i d m o t i o n w i t h l i g h t l o a d s , as i n t h e swing phase o f
walking.
( 9 2 , 9 5 , 96)
T h i s m o d i f i c a t i o n o f t h e hydrodynamic
d e v e l o p e d when i t was s e e n t h a t f o r c e s w i t h i n
an e l a s t i c d e f o r m a t i o n
o f the c a r t i l a g e .
g e n e r a t e a t h i c k e r wedge o f l u b r i c a t i n g
s y n o v i a l j o i n t s c o u l d produce
This d e f o r m a t i o n
cartilages
can be seen t o
f l u i d . (95)
As mentioned i n t h e d i s c u s s i o n o f t h e u l t r a s t r u c t u r e
c a r t i l a g e , scanning
theory
of a r t i c u l a r
e l e c t r o n m i c r o g r a p h s have shown the s u r f a c e o f t h e s e
t o be r e l a t i v e l y r o u g h . (97)
Thus has d e v e l o p e d t h e combined
theory of "boosted l u b r i c a t i o n " f o r a r t i c u l a r c a r t i l a g e s .
t h e o r y s u g g e s t s t h a t as p r e s s u r e
i s a p p l i e d across
( 9 2 , 97)
This
a j o i n t , o p p o s i n g peaks
o f c a r t i l a g e meet, and between t h e s e peaks boundary l u b r i c a t i o n i s a c t i v e .
P o o l s o f s y n o v i a l f l u i d accumulate i n t h e d e p r e s s i o n s
As t h e p r e s s u r e
between t h e p e a k s .
r i s e s , w a t e r and o t h e r low m o l e c u l a r w e i g h t s u b s t a n c e s
d i f f u s e between the pores o f the c a r t i l a g e and c o l l e c t i o n s
hyaluronate
r i c h f l u i d a r e g e n e r a t e d . (94)
vides a modified
f l u i d f i l m f o r further
of v i s c o u s ,
This h i g h l y v i s c o u s f l u i d
l u b r i c a t i o n . (92)
A r e c e n t s t u d y measured t h e t h i c k n e s s o f s y n o v i a l f l u i d f i l m s
h e a l t h y and a r t h r i t i c j o i n t s .
I t was n o t e d t h a t b o t h f l u i d
i n thickness w i t h the a p p l i c a t i o n
f i l m was always c o n s i d e r a b l y l e s s .
pro-
films
of l o a d , but that the a r t h r i t i c
from
decreased
fluid
F u r t h e r m o r e , t h e t h i c k n e s s o f the f l u i d
f i l m from d i s e a s e d j o i n t s c o u l d be made t o approach t h a t o f normal
fluid
- 32 by t h e a d d i t i o n o f sodium c h l o r i d e .
The d i f f e r e n c e i n t h e t h i c k n e s s o f t h e
f l u i d f i l m s was f e l t t o be due t o a d i f f e r e n c e i n t h e number o f e l e c t r i c a l
r e p u l s i v e f o r c e s adsorbed o n t o n e g a t i v e l y charged s u r f a c e m o l e c u l e s . (98)
To date t h e o n l y r e c o r d e d measurements o f s y n o v i a l f l u i d
are
electrolytes
t h o s e w h i c h have been o b t a i n e d u s i n g flame p h o t o m e t r y . ( 6 2 , 66)
These
values correspond t o the t o t a l c o n c e n t r a t i o n of the e l e c t r o l y t e i n q u e s t i o n .
However, r e c e n t advances
i n the use of c a t i o n s e n s i t i v e g l a s s
electrodes
have e n a b l e d i n v e s t i g a t o r s t o measure t h e i o n i z e d f r a c t i o n o f v a r i o u s
electrolytes i n biological fluids.
the
( 9 9 , 100)
I t has been s u g g e s t e d t h a t
c a t i o n i c f r a c t i o n o f these e l e c t r o l y t e s represent t h e i r
biologically
a c t i v e p a r t ( 9 9 ) , and i t was e l e c t e d t o s u b j e c t s y n o v i a l f l u i d samples t o
such an a n a l y s i s .
I t was f e l t t h a t i f a r t h r i t i c
f l u i d had l e s s
biologically
a c t i v e f o r c e s t h i s might a c c o u n t f o r t h e breakdown o f l u b r i c a t i o n found i n
arthritic
joints.
Method
S i x t y - o n e samples o f s y n o v i a l f l u i d were o b t a i n e d a t a r t h r o t o m y o r by
a s p i r a t i o n , and t h e s e were d i v i d e d i n t o 2 g r o u p s .
rheumatoid a r t h r i t i s .
E l e v e n p a t i e n t s had
The r e m a i n i n g f i f t y s u f f e r e d from c o n d i t i o n s n o t
a s s o c i a t e d w i t h rheumatoid a r t h r i t i s ;
the m a j o r i t y having arthrotomy of the
knee f o r i n t e r n a l derangement o r f o r m i n i s c a l t e a r s .
The mean age o f t h e
r h e u m a t o i d group was 48.7, and t h e r e was a predominance
non-rheumatoid
of females.
I n the
group, t h e mean age was 35.4 and t h e r e were more m a l e s .
- 33 TABLE I - Sex and Age o f E x p e r i m e n t a l
Sample
Rheumatoid Group
11 ( 7 f e m a l e ,
4 male)
Mean Age
48.7
Non-Rheumatoid Group
50 (15 f e m a l e , 35 male)
Mean Age
35.4
61
Total
The
samples were a n a l y z e d
f o r i o n i z e d sodium and p o t a s s i u m u s i n g
flow-
t h r o u g h e l e c t r o d e s c o n n e c t e d i n s e r i e s and s h i e l d e d i n a m e t a l b o x . The
r e s u l t i n g e l e c t r o d e p o t e n t i a l s were r e a d on two V i b r o n E l e c t r o m e t e r s
were c a l i b r a t e d d a i l y u s i n g weighed s t a n d a r d s .
The samples were
t o f u r t h e r a n a l y s i s u s i n g the Techtron Atomic A d s o r p t i o n
which
subjected
Spectrophotometer
and, when volume p e r m i t t e d , t h e pH o f the sample was d e t e r m i n e d .
Results
The mean c o n c e n t r a t i o n o f sodium i o n s i n t h e r h e u m a t o i d group was
139.0
mEq/litre.
T h i s was compared t o a mean o f 148.9 m E q / l i t r e i n t h e
non-rheumatoid g r o u p .
concentrations
2.57
There was l i t t l e d i f f e r e n c e i n t h e p o t a s s i u m i o n
i n t h e two g r o u p s , t h e mean l e v e l s b e i n g 2.52 m E q / l i t r e and
mEq/litre respectively.
- 34 TABLE I I - Sodium and P o t a s s i u m I o n C o n c e n t r a t i o n s
i n Synovial Fluid of
Rheumatoid and Non-Rheumatoid P a t i e n t s Measured w i t h G l a s s E l e c t r o d e s .
[Na ]
+
Rheumatoid Group
139.0 mEq/1
(Range 135 mEq/1 - 146 mEq/1)
( S t a n d a r d D e v i a t i o n 3.16 mEq/1)
Non-Rheumatoid Group
148.9 mEq/1
(Range 141 mEq/1 - 154 mEq/1)
(Standard
D e v i a t i o n 3.31 mEq/1)
[K ]
+
Rheumatoid Group
2.52 mEq/1
(Range 1.6 mEq/1 - 2.8 mEq/1)
( S t a n d a r d D e v i a t i o n 0.41 mEq/1)
Non Rheumatoid Group
2.57 mEq/1
(Range 1.8 mEq/1 - 3.0 mEq/1)
( S t a n d a r d D e v i a t i o n 0.49 mEq/1)
When t h e samples were s u b j e c t e d t o a n a l y s i s u s i n g t h e s p e c t r o p h o t o meter, a s i m i l a r
t r e n d was n o t e d .
The r h e u m a t o i d group had a mean concen-
t r a t i o n o f 130.7 m E q / l i t r e compared t o 135.7 m E q / l i t r e i n t h e nonr h e u m a t o i d group, w h i l e p o t a s s i u m c o n c e n t r a t i o n s were 4.3 m E q / l i t r e and
4.7 m E q / l i t r e .
The l o w e r c o n c e n t r a t i o n s
o f sodium seen u s i n g t h e s p e c t r o -
photometer were f e l t t o be due t o b o t h t h e h i g h p r o t e i n c o n t e n t
f l u i d , and t o a d i l u t i o n a l phenomenon.
of the
- 35 TABLE
III
Sodium
Rheumatoid
and P o t a s s i u m
Concentrations
and Non-Rheumatoid
Patients
i n Synovial
Fluid of
Measured w i t h t h e
Spectrophotometer
[Na]
Rheumatoid
Group
130.7 mEq/1
(Range 128 mEq/1 - 136 mEq/1)
(Standard
Non-Rheumatoid
Group
135.7 mEq/1
Deviation
4.5
mEq/1)
(Range 120 mEq/1 - 142 mEq/1)
(Standard
Deviation
5.4
mEq/1)
[K]
Rheumatoid
Group
4.3
(Range 3.9 mEq/1 - 4.7 mEq/1)
mEq/1
(Standard
Non-Rheumatoid
Group
4.7
mEq/1
analysis
o f the synovial
have
a c o n s i s t e n t l y lower
7.10
a n d 7.42 r e s p e c t i v e l y .
TABLE
IV
pH t h a n
Synovial
fluid
pH showed
the second
Deviation
group,
t h e mean
Non-Rheumatoid
Group
mEq/1)
group t o
levels
being
Patients
pH
Group
mEq/1)
0.55
the rheumatoid
mEq/1)
pH i n R h e u m a t o i d a n d
Non-Rheumatoid
Rheumatoid
0.33
( R a n g e 3.4 mEq/1 - 6.5
(Standard
An
Deviation
Range
7.10 mEq/1
(6.9 mEq/1 - 7.3 mEq/1)
7.42 mEq/1
(7.25
mEq/1 - 7.53 mEq/1)
- 36 The
lytes
question
arose
as
to whether
reflected differences
the
TABLE V
levels
i n a number
found
and
of
in synovial
(By
electro-
Serum e l e c t r o l y t e
patients,
in synovial
Serum E l e c t r o l y t e s
Rheumatoid
difference
i n serum c o n c e n t r a t i o n s .
determinations were a v a i l a b l e
correlation with
the
and
showed
no
fluid.
Flame
Non-Rheumatoid
Photometry)
in
Patients.
[Na]
[K]
Rheumatoid Group
(Mean)
139
mEq/1
(Mean)
4.3
mEq/1
Non-Rheumatoid Group
(Mean)
140
mEq/1
(Mean)
4.4
mEq/1
All
of
difference
fluid
the
in
above r e s u l t s were s u b j e c t e d
the
s o d i u m was
two
groups
found
to
be
i n glass
highly
to
electrode
statistical
analysis.
determinations
of
The
synovial
s i g n i f i c a n t . (p<0.0001)
Discussion
This
paper
mechanisms
number
of
of
was
appear
found
to
be
the
less
electrical
fluid
films.
fluid
films
could
the
addition
years.
active
than
those
of
This
be
to
explain
are
(101)
of
active
Fluid
was
made t o
fluid
of normal
forces
one
seen i n rheumatoid
films
were
films
approach
of
electrolyte solutions.
by
fluid,
for
thickness
(98)
fact
of
That
j o i n t s has
boundary
joint
the
possible
arthritis.
and
responsible
the
the
the
be-
When i t
joints
i t was
a
lubrication
movement.
from a r t h r i t i c
synovial
substantiated
of
in synovial
i n d i f f e r e n t phases
thickness
repulsive
these
by
attempt
c a r t i l a g e wear
i n recent
that
considerably
that
the
an
l u b r i c a t i o n mechanisms
come o b v i o u s
both
represents
was
suggested
maintenance
that
the
normal
of
arthritic
fluid
films
- 36a
This
s t u d y has
significantly
as
may
compared
be
due
joints,
The
less
may
lower
ly
a diminution
part,
free
repulsive
i n the
fluid
samples
concentration
concentration
the e l e c t r i c a l
as
bind
the c o n c e n t r a t i o n
from non-rheumatoid
t o the h i g h e r
in
in
i n synovial
t o samples
which
lubrication
shown t h a t
-
fluid
sodium
ions.
film
the c a r t i l a g e a t t r i t i o n
patients.
seen
found
sodium w i l l
acting within
fluid
This
is
arthritics,
difference
i n rheumatoid
(66)
thickness.
a r e s u l t of thinned
sodium
from rheumatoid
of protein
of ionized
forces
of ionized
result in a
a joint,
Thus,
subsequent-
a breakdown i n
films results.
in arthritic
and
decrease
This
joints.
may
explain,
- 37 CONCLUSION
Advances i n t h e knowledge o f s y n o v i a l j o i n t anatomy and p h y s i o l o g y
have p a r a l l e l e d s i m i l a r advances i n o t h e r b i o l o g i c a l f i e l d s .
s y n o v i a l membrane h a s ,
i n the past, a t t r a c t e d the greatest
Although the
attention with
r e g a r d t o t h e p a t h o g e n e s i s o f j o i n t d i s e a s e , new i n t e r e s t i s now b e i n g
f o c u s e d on a l t e r a t i o n s i n a r t i c u l a r c a r t i l a g e . As i t i s on c a r t i l a g e
i n t e g r i t y t h a t u s e f u l j o i n t f u n c t i o n depends, a breakdown i n t h i s
integrity,
e i t h e r mechanically or biochemically, r e s u l t s i n loss of function.
Loss o f
f u n c t i o n i n o n l y one o f t h e many s y n o v i a l j o i n t s o f t h e body c a n r e s u l t i n
great l i m i t a t i o n o f an i n d i v i d u a l ' s c a p a c i t y .
Thus a g r e a t e r
understanding
of t h e u l t r a s t r u c t u r e and m e t a b o l i s m o f s y n o v i a l j o i n t s and t h e changes
that occur w i t h the i n t r o d u c t i o n o f pathology, i s leading basic
and
scientists
c l i n i c i a n s c l o s e r t o an u n d e r s t a n d i n g o f t h e p a t h o g e n e s i s o f t h e v a r i o u s
arthritidies.
The c o m p l e x i t y o f t h e s e f i n d i n g s i s r e f l e c t e d by t h e r e c e n t
l i t e r a t u r e d e a l i n g w i t h t h e p a t h o g e n e s i s o f r h e u m a t o i d a r t h r i t i s . (102, 103)
T h i s paper i s an a t t e m p t t o r e v i e w t h e s t r u c t u r e and f u n c t i o n o f
normal s y n o v i a l j o i n t s , w i t h p a r t i c u l a r r e f e r e n c e
a s p e c t s o f t h e i r anatomy.
t o the u l t r a s t r u c t u r a l
I n a d d i t i o n , a review o f the c u r r e n t
o f j o i n t l u b r i c a t i o n i s i n c l u d e d , and a t h e o r y o f d i s o r d e r e d
derived
is
concepts
lubrication,
f r o m t h e r e s u l t s o f e x p e r i m e n t a l work c o n d u c t e d on s y n o v i a l
fluid,
presented.
R e s e a r c h c o n t i n u e s i n many r e l a t e d f i e l d s , i n c l u d i n g
of p r o s t h e t i c j o i n t s
(106)
(104,
105),
reimplantation
and t h e use o f a r t i f i c i a l l u b r i c a n t s .
I t i s , however, t h r o u g h a g r e a t e r u n d e r s t a n d i n g o f t h e b a s i c
rela-
t i o n s h i p between t h e s t r u c t u r e and m e t a b o l i s m o f b i o l o g i c a l t i s s u e s and
t h e i r u l t i m a t e f u n c t i o n t h a t answers t o many unanswered q u e s t i o n s w i l l be
found.
- 38 H u n t e r d e s c r i b e d t h e p e n u l t i m a t e r e s u l t o f a d i s e a s e d j o i n t i n 1743,
and c o n c l u d e d :
" a t l a s t t h e unhappy P e r s o n must submit t o E x t i r p a t i o n , a
d o u b t f u l Remedy, o r wear out a p a i n f u l , though p r o b a b l y a s h o r t L i f e . " (1)
His
c o n c e r n was as a p p r o p r i a t e a t t h a t time as i t w o u l d be t o d a y .
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