ABNORMAL CONDITIONS OF THE KNEE-JOINT. 



73 



also a displacement more or less considerable 

 according to the degree of displacement of the 

 tibia. In these incomplete dislocations of the 

 knee-joint, the patella, it is said, suffers but 

 little displacement, its long axis only becoming 

 oblique, and the lower point of the patella being 

 directed either outwards or inwards, towards 

 the tubercle of the tibia, according to the nature 

 and direction of the dislocation. These are 

 the opinions of Boyer, who evidently has not 

 witnessed many cases of either complete or 

 incomplete dislocations of the knee-joint. From 

 what we ourselves have noticed of the situation 

 the patella takes when the bones are displaced 

 under the influence of disease, we should be 

 disposed to believe that even in partial luxa- 

 tion of these bones laterally particularly in 

 the dislocation of the femur inwards and of the 

 tibia outwards in this case the patella would 

 be thrown completely over the trochlea and lie 

 on the outer side of the external condyle, as in 

 Jig. 6 and 8. If the limb be flexed and at the 

 same time the tibia everted, such an event 

 appears almost inevitable. 



Dislocations of the patella. Although the 

 patella is not articulated with the tibia, never- 

 theless 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. 

 Authors 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 

 cannot descend beneath its usual place unless 

 the extensor muscles of the leg be torn from 

 their attachment to its upper margin ; nor can 

 this bone be elevated above its usual situation 

 unless the ligamentum patellae be ruptured. 

 Luxations of the patella then may take place 

 in the direction inwards or outwards. The 

 latter is decidedly the more common. Either 

 luxation may be complete or incomplete. 

 (Boyer.) 



Complete luxation of the patella outwards. 

 In this accident the patella is thrown com- 

 pletely 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 

 os femoris, and its anterior or subcutaneous 

 surface is turned completely outwards. In 

 this case the ligamentum patellae 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 

 seventy of the pain when he attempts to do so, 

 and by the depression which is observed to 

 exist 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 



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 attachments 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 patellae 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. 



