KNOCK-KNEE
PROCEDURE FOR A KNEE REPLACEMENT
This procedure is carried out to
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l1
1
replace a diseased or eroded knee
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joint. The surgeon usually makes
F e m u r
a long, straight incision, cutting
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1
through the joint capsule and
S k in in c i s i o n
synovial membrane, then pushes
aside the patella to reach the joint.
Special instruments are used to make
.. 'S
precise measurements and cut away
areas of bone so that the artificial
knee replacement components will
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fit and move correctly.
I
The lower end of the femur (thigh-
bone) is shaped and holes are drilled
into itto acceptthe femoral component of
the prosthesis (see inset). Accuracy is
achieved by using the surgical equivalent
ofa mitre box.
2
The upper end ofthe tibia (shin-bone)
is shaped, and holes are drilled into it
to acceptthe tibial component ofthe
prosthesis. The cutting and drilling ofthe
bone are again carried out using the special
orthopaedic instruments.
3
Often the patella is left undamaged, but
repairs may be carried out to its surface.
In this case, the back part ofthe patella is
cut away to leave a flat surface. Small holes
are then drilled into this surface to accept
the patellar component ofthe artificial joint.
4
After achieving a satisfactory fit using trial
components, the three parts ofthe final
prosthesis are then cemented in place. Any
excess cement is then removed from around
the new joint and a final check is made of
the joint movements.
F e m u r
T ib ia
X-ray of arthritic knee
Severe wear and tear ofthe
bone and cartilage can easily
be seen on this knee X-ray.
Knee prosthesis
The main artificial components
fit over the femur and tibia (the
patellar component is not
shown). The prostheses come
in differenttypes and sizes.
X-ray of artificial knee
This X-ray shows the three
components ofthe prosthesis
in position after surgery.
t h e
j o i n t
p r e v e n t
o v e r s t r a i g h t e n i n g
a n d
o v e r b e n d i n g . T h e q u a d r i c e p s m u s c l e s , a t
t h e
f r o n t
o f
t h e
t h i g h ,
s t r a i g h t e n
t h e
k n e e , a n d t h e h a m s t r i n g m u s c l e s a t t h e
b a c k o f t h e t h i g h b e n d i t .
DISORDERS
I n j u r i e s o f t h e k n e e a r e c o m
m o n , a n d
i n c l u d e
l i g a m e n t s p r a i n s ,
t o r n
m e n i s -
c u s ,
d i s l o c a t i o n
o f
t h e
p a t e l l a ,
a n d
f r a c t u r e
o f a n y o f t h e b o n e s . A p a i n f u l
i n f l a m m a t o r y c o n d i t i o n ,
c h o n d r o m a l a c i a
p a t e l l a e
,
i s c o m
m o n i n a d o l e s c e n t s , a n d
k n o c k - k n e e
a n d
b o w l e g
a r e c o m
m o n t e m
-
p o r a r y d e f e c t s i n c h i l d r e n .
k n e e c a p
S e e
p a t e l l a
.
k n e e -je rk re fle x
A n i n v o l u n t a r y r e s p o n s e , a l s o k n o w n a s
a p a t e l l a r r e f l e x , t h a t o c c u r s w h e n t h e
t e n d o n j u s t b e l o w t h e k n e e c a p ( p a t e l l a )
i s t a p p e d . T h e t e n d o n s t r e t c h e s a n d t h e
t h i g h
m u s c l e s
c o n t r a c t ,
s t r a i g h t e n i n g
t h e k n e e . ( S e e a l s o
r e f l e x .
)
k n e e -jo in t re p la c e m e n t
S u r g e r y t o r e p l a c e a d i s e a s e d
k n e e
j o i n t
w i t h a n a r t i f i c i a l o n e , u s u a l l y m a d e o f
m e t a l o r p l a s t i c . K n e e - j o i n t r e p l a c e m e n t
i s m o s t c o m
m o n l y c a r r i e d o u t o n o l d e r
p e o p l e w h o s e k n e e s a r e s e v e r e l y a f f e c -
t e d
b y
t h e
i n f l a m m a t o r y
c o n d i t i o n s
o s t e o a r t h r i t i s
o r
r h e u m a t o i d a r t h r i t i s
.
K n ie s t s y n d ro m e
A v e r y r a r e i n h e r i t e d
d i s o r d e r
d u e t o
a b n o r m a l c o l l a g e n
( a p r o t e i n i n b o n e ,
c a r t i l a g e , a n d c o n n e c t i v e t i s s u e ) . I t c a u s -
e s s e v e r e d w a r f i s m ( s e e
s h o r t s t a t u r e )
w i t h
c u r v a t u r e o f t h e s p i n e
(
k y p h o s c o l i o s i s
).
k n o c k -k n e e
I n w a r d c u r v i n g o f t h e l e g s s o t h a t t h e
k n e e s t o u c h , c a u s i n g t h e f e e t t o b e p o s i -
t i o n e d f u r t h e r a p a r t t h a n n o r m a l .
CAUSES
K n o c k - k n e e
i s
c o m
m o n
i n
c h i l d r e n
b e t w e e n t h e a g e s o f t h r e e a n d f i v e a n d
m a y b e p a r t o f n o r m a l d e v e l o p m e n t . I n
s o m e
c h i l d r e n ,
k n o c k - k n e e
m a y
b e
c a u s e d b y
r i c k e t s
,
a d i s e a s e t h a t s o f t e n s
t h e
b o n e s .
I n
a d u l t s ,
c a u s e s
i n c l u d e
o s t e o a r t h r i t i s
a n d
r h e u m a t o i d a r t h r i t i s
o f
t h e
k n e e .
A
l e g
f r a c t u r e
t h a t
h a s
n o t
h e a l e d c o r r e c t l y m a y a l s o c a u s e k n o c k -
k n e e i n c h i l d r e n o r a d u l t s .
TREATMENT
I n c h i l d r e n , t h e c o n d i t i o n u s u a l l y d i s a p -
p e a r s b y a b o u t s e v e n y e a r s . K n o c k - k n e e
t h a t p e r s i s t s , o r i s d u e t o a d i s o r d e r , m a y
r e q u i r e
o s t e o t o m y
,
a s u r g i c a l p r o c e d u r e
K
453
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