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Structure and function of synovial joints, with particular reference to the mechanism of their lubrication Piper, Michael Stafford 1972

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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 . 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