PRACTICAL CONSIDERATIONS : SPINAL CORD. 1053 



\n fracture-dislocatio?is of the spine it is the body of the vertebra which is most 

 frequently fractured, the hgaments yielding- posteriorly and permitting the dislocation. 

 The fractured edges of bone are, therefore, in front of the cord ; and, as the upper 

 fragment passes forward, the anterior or motor portion of the cord is pressed 

 and crushed against the sharp upper edge of the lower fragment. In partial 

 transverse lesions of the cord the paralysis below the lesions affects, therefore, the 

 motor columns of the cord more than the sensory columns which are in part 

 posterior. 



The most frequent seat of fracture-dislocation of the spine is in the thoraco- 

 lumbar region (page 145). Fortunately, it is this variety which offers the best 

 prognosis, since the cord ends usually just below the lower border of the first 

 lumbar vertebra, and the cauda equina being more movable and tougher than the 

 cord itself, it can better evade the encroachment on the canal, although in spite of 

 these facts, it is not infrequently injured in such lesions. The bodies of the lumbar 

 vertebrae are the largest and most cancellous, the intervertebral discs the thickest 

 and most elastic, so that crushing of them occurs with less tendency to invade the 

 canal and injure the cord than in any other portion of the spine. 



In caries of the spine (Pott's disease) the lesion is situated in the bodies of the 

 vertebrae, and therefore, in front of the cord. As the inflammatory exudate extends 

 it will invade the spinal canal anteriorly, often producing an external pachymeningitis. 

 The irritation and pressure resulting will again affect the motor portion of the cord, 

 first producing a paralysis of motion in the parts below, varying in degree according 

 to the amount of pressure on the cord. If sensation is impaired it is a later 

 phenomenon and is due to greater pressure upon the cord, and in some cases to 

 myelitis. The loss of motion is often the only effect produced. If the lower cervical 

 region is involved by the lesion the phrenic nerves will escape paralysis, but the 

 arms, trunk, bladder, rectum, and lower extremities will be affected. Since the 

 intercostal and abdominal muscles are involved in the paralysis, breathing will be 

 difficult and will depend upon the action of the diaphragm only. Thus as the lesion 

 occurs ar successively lower levels, the highest limits of the paralyzed area descend, 

 and the expectation of life increases. 



In the cervical and thoraco-lumbar regions where the injuries to the spine and 

 the cord are most frequent, are situated the two enlargements of the cord. The 

 cervical begins at the fourth cervical vertebra, gradually reaches its largest diameter 

 opposite the fifth and sixth vertebrae,' and then gradually decreases to the first 

 thoracic, where it merges into the thoracic portion of the cord. Only in the thoracic 

 region does the circumference of the cord remain the same throughout. The lumbar 

 enlargement is shorter than the cervical and begins opposite the tenth thoracic 

 vertebra, gradually increases to the twelfth thoracic, after which it gradually decreases 

 to the conus medullaris. 



The localization of lesions of the cord, producing symptoms of paralysis, will depend 

 upon the height and extent of the paralyzed areas. It must be borne in mind that the 

 nerve-roots arise from the cord usually at a level higher than the foramina through 

 which they escape from the spinal canal. The first and second cervical nerve-roots 

 pass out of the canal almost horizontally. The intraspinal course of the succeeding 

 nerve-roots increases gradually in obliquity so that the spinous processes of the second, 

 third and fourth vertebrae correspond approximately to the level of the third, fourth 

 and fifth cervical nerve-roots. The seventh cervical spine corresponds to the first 

 thoracic nerve-root. The spinous process of the fifth thoracic vertebra is on a 

 level with the seventh thoracic nerve, and the spine of the tenth thoracic vertebra 

 with the origin of the second lumbar nerve. The first lumbar nerve arises just below 

 the ninth thoracic spine, the second lumbar nerve opposite the tenth thoracic 

 spine, the third and fourth lumbar nerves opposite the eleventh spine, and the 

 fifth lumbar and the first sacral nerves between the eleventh and twelfth thoracic 

 spines. 



Only the spinous processes can be our surface guides, and it must be borne in 

 mind that they are not always on the level of their corresponding vertebrae. Briefly, 

 it may be said that the eight cervical nerves arise from the cord between the lower 

 margin of the foramen magnum and the sixth cervical spine, the first six thoracic 



