also a displacement more or less considerable 
ecording to the degree of displacement of the 
tibia. In these incomplete dislocations of the 
nee-joint, the patella, it is said, suffers but 
ittle displacement, its long axis only becoming 
blique, and the lower point of the patella being 
directed either outwards or inwards, towards 
he tubercle of the tibia, according to the nature 
nd direction of the dislocation. These are 
he opinions of Boyer, who evidently has not 
fitnessed many cases of either complete or 
acomplete dislocations of the knee-joint. From 
hat we ourselves have noticed of the situation 
he patella takes when the bones are displaced 
nder the influence of disease, we should be 
ed to believe that even in partial luxa- 
on of these bones laterally—particularly in 
ie dislocation of the femur inwards and of the 
bia outwards—in this case the patella would 
s thrown completely over the trochlea and lie 
m the outer side of the external condyle, as in 
e.6and 8. If the limb be flexed and at the 
ame time the tibia everted, such an event 
s almost inevitable. 
locations of the patella—Although the 
atella is not articulated with the tibia, never- 
heless it is so strongly attached to this bone 
by ligament that the leg cannot be luxated 
“from the femur without the patella necessarily 
_ undergoing a change of place ; but the patella 
“may be luxated independently of the tibia. 
juthors speak of luxations of the patella in 
the directions upwards, downwards, inwards, 
and outwards ; but of these the two last alone 
deserve the name of luxations. The patella 
“annot descend beneath its usual place unless 
the extensor muscles of the leg be torn from 
cir attachment to its upper margin ; nor can 
is bone be elevated above its usual situation 
unless the ligamentum patella be ruptured. 
-Luxations of the patella then may take place 
‘im the direction inwards or outwards. The 
‘Tatter is decidedly the more common. Either 
_ luxation may be complete or incomplete. 
(Boyer. 
Da lCoapicte luxation of the patella outwards.— 
In this accident the patella is thrown com- 
Bletely off the articular trochlea of the femur. 
The internal edge of the bone is directed for- 
wards, its external edge backwards; its pos- 
terior cartilaginous surface is applied to the 
Outer surface of the external condyle of the 
0s femoris, and its anterior or subcutaneous 
gi is turned completely outwards. In 
is case the ligamentum patelle is somewhat 
twisted on itself, and its direction rendered 
oblique. ’ 
We recognize the complete luxation out- 
wards by the extended condition of the pa- 
tient’s limb, by his inability to flex it, by the 
| Severity of the pain when he attempts to do so, 
_ and by the depression which is observed to 
 €xist in the place the patella had abandoned, 
_ (at the bottom of which depression we can 
easily distinguish the articular pulley of the 
femur); finally, by the tumour formed by the 
_ Patella on the anterior part of the tuberosity of 
the external condyle of this bone. The acci- 
_ dent usually occurs to a person who, while 
‘¢ 
ABNORMAL CONDITIONS OF THE KNEE-JOINT. 
73 
walking or running, falls with the knee turned 
inwards and foot outwards, and thus by the 
violent action of the extensor muscles instinc- 
tively exerted to prevent the fall the patella is 
drawn over the external condyle of the os fe- 
moris. When the person rises he finds him- 
self unable to bend or extend his leg, and the 
muscles and ligaments of the patella are on 
the stretch. This accident is generally the 
effect of muscular action, but the dislocation 
may result from accidental force acting on the 
patella. 
In the greatest possible flexion of the leg the 
patella is too much sunk between the condyles 
of the femur, and is too strongly applied 
against these eminences by its ligament and by 
the tendon of the extensor muscles, to permit 
it to yield to the action of external force. But, 
on the contrary, when the leg is moderately 
extended, these attychments are relaxed; the 
bone projects more, and enjoys greater mo- 
bility, which renders it susceptible of yielding 
and of being displaced either outwards or in- 
wards according to the direction of the impelling 
force. The luxation outwards, more easy and 
more frequent than that inwards, is ordinarily, as 
we have stated, the effect of a force acting upon 
the internal edge of the patella, by which this 
bone is pushed outwards, the leg being at the 
time either extended or moderately flexed. 
The natural prominence of the internal border 
of the patella renders it liable to be acted upon 
by blows, &c., and to be from this cause fre- 
quently thrown outwards over the external con- 
dyle of the femur. 
The patella is sometimes dislocated spon- 
taneously in persons of weak habit and of lax 
fibre, as it is denominated. If a person of this 
constitution be so malformed that the knees 
are directed too much inwards, the patella are 
from this cause still more predisposed to spon- 
taneous luxation. The mere circumstance of 
the existence of a faulty inclination of the 
knees inwards is not sufficient in itself to pre- 
dispose a patient strongly to a dislocation of the 
patella outwards; but when such a malforma- 
tion coincides with an habitual state of mus- 
cular relaxation, this spontaneous luxation is 
likely to occur. 
Luxation of the patella inwards.—This lux- 
ation is much less frequent than that outwards. 
It happens from falls against a projecting body, 
by which the patella is struck upon its outer 
side, the leg being at the time of the fall turned 
inwards. We require no other signs to enable 
us to recognize this accident than the cavity we 
notice in the place the bone has left, and the 
eminence it forms in the place to which it has 
been transferred, namely, on the internal side 
of the inner condyle of the femur. 
Incomplete luxation of the patella— The 
signs of this incomplete luxation are so evi- 
dent* that it is impossible to mistake them. 
The leg is extended, and if we endeavour to 
flex it, the pain the patient suffers is conside- 
rably increased. The natural form of the knee 
is altered; we perceive through the skin the 
* Boyer. 
