452 
W. L. WIT.LTAMS. 
inents and tissues involved, so that the longer and thinner in¬ 
ternal tibio-patellar ligament would yield more readily than the 
shorter, thicker and stronger external, thus guiding the patella 
outwards, which is further greatly favored by the disposition of 
the powerful long vastus muscle, which through its attachment 
to the external ligament exerts an abducting power upon the 
patella which the adductors do not fully counterbalance upon 
this bone, hence we recognize as factors in oiitward luxation 
the lesser external ridge, the lesser strength of internal tibio-pa¬ 
tellar ligament and the superior abducting power on the patella 
of the long vastus muscle. 
The degree of luxation was evidently intensified by being 
bilateral so that any effort on the part of the patient to rise could 
not be centred on a sound limb, but must fall alike on each of 
two members, neither of which was capable of bearing weight ex¬ 
cept by an outward dragging upon the patella, which, buoyed 
out beyond its groove, was readily drawn from its normal loca¬ 
tion. 
The case serves to illustrate, too, what the writer has long 
maintained, two generically different forms of patellar luxation, 
the “ floating ” form occurring almost wholly in young animals 
and caused chiefly by navel infection and inckets^ in which, 
buoyed up beyond its groove by a hydrarthrosis, the patella tends 
to pass outward during flexion when the crural triceps and con¬ 
sequently the internal tibio-patellar ligament is relaxed and in¬ 
wards during extension, thus denuding and in time wearing 
away the external ridge of the femoral trochlea ; and the trau¬ 
matic or direct form, in which the luxation is suddenly pro¬ 
duced by violence. 
An important fact well emphasized in this case is the value 
of preventing in young animals the accumulation of sufficient 
synovia in the femoro-patellar articulation to buoy the patella 
outwards beyond the level of the trochlear ridges, which is to 
be accomplished by sufficiently frequent aspirations of the fluid 
in conjunction with the injection of appropriate remedies into 
the synovial sac. 
