464 
FRACTURES OF THE VERTEBRA. 
(2) The second action likely to produce this accident is excessive lateral 
thrust on the spinal column produced by unilateral contraction of the 
dorsal muscles. It occurs from lifting the hindquarters from the bed, 
and is probably favoured by anchylosis of the vertebrae or ossification of 
the inter-vertebral discs. Ercolani and many others have drawn attention 
to the predisposing influence exerted, under these circumstances, by bony 
union of the vertebrae. This is probably the chief reason why old horses 
so often suffer from fracture of the vertebrae. Such fracture is commonest 
during dental operations and the castration of thoroughbred horses. The 
necessity for dental operations is greatest in old horses, whose bones are 
less resistant than those of younger animals. In castration fracture 
generally occurs at the moment when the clams are applied to the 
spermatic cord, and in this case is due to the violent muscular move¬ 
ments. Fractures of the vertebrse occur most frequently when the animal 
Fig. 180 .—Fracture (by crushing) of the body of a vertebra. 
is lying on its side, seldom when on its back; Moller only met with one 
of the latter, and of Dieckerhoff’s fourteen cases only one was produced 
in the dorsal position. 
Fractures may perhaps be favoured by disease of the spinal column. 
Thiimmler describes abnormal fragility of the ribs and vertebrae in a 
ten year old mare ; Lehnert, a case of vertebral fracture, favoured by 
caries, resulting from an abscess. Paltz mentions a case of osteomalacia 
in a horse ; after several minor fractures had occurred, the 3rd lumbar 
vertebra was broken, with fatal results. On post-mortem examination, 
all the bones were found excessively soft—the transverse processes of 
the lumbar vertebrse particularly so. Degive also recognises such a 
predisposition. 
With few exceptions the fracture occurs either in the last dorsal or first 
lumbar vertebra, which are not only the weakest, but lie in the middle 
of the mobile column, which, like a stick, if excessively bent, breaks most 
readily in the centre. But falling over backwards, and other accidents, 
may also cause fracture of the anterior dorsal or lumbar vertebrae. 
