THE SPINAL MEDULLA 529 



partial or complete. In some cases the dislocation may be 

 reduced spontaneously ; in others, the condition may be mistaken 

 for a stiff or sprained neck and the correct diagnosis may be made 

 only after radiographic examination. The inferior articular 

 process slips forwards over the superior articular process of the 

 vertebra below, and it may compress the spinal nerve, giving 

 rise to referred pain over its cutaneous distribution. This injury 

 usually occurs between the third and fourth, fourth and fifth, 

 or fifth and sixth cervical vertebrae, and it may be accompanied 

 by bruising of the spinal medulla and extravasation of blood 

 into or around the spinal medulla (Fig. 162). The resulting 

 sensory and motor changes depend on the extent of the lesion. 



Bilateral dislocations are always accompanied by serious 

 injury of the spinal medulla, and, when they affect any of the 

 upper four cervical segments, death is instantaneous, as the 

 diaphragm (phrenic nerve, C. 3, 4, and 5) and the other muscles 

 of respiration are all paralysed. 



Fracture dislocation, which is a not uncommon injury, 

 usually occurs in the lumbar or lower thoracic region. The 

 upper vertebra passes forwards and the spinal medulla is crushed 

 between its laminae and the upper border of the body of the 

 vertebra below. A complete transverse lesion of the spinal 

 medulla generally results, but sometimes the injury is only 

 partial. It may, at first, be impossible to determine whether 

 the lesion is complete or only partial, as in the latter case the 

 amount of paralysis is increased by the pressure of the accom- 

 panying extravasation of blood. When the injury is incomplete, 

 gradual improvement occurs as the extravasated blood becomes 

 absorbed. In these cases the motor changes are usually more 

 extensive than the sensory changes. 



A complete transverse lesion of the spinal medulla is 

 accompanied by total sensory and motor paralysis of the regions 

 which are innervated by the segments below the lesion. As the 

 upper neurone is involved, the paralysed muscles are spastic, 

 and although they may atrophy from disuse, they do not give 

 the reaction of degeneration. In the case of the muscles which 

 are innervated by the actual segment destroyed by the injury, 

 the lesion is of the lower neurone type. Consequently these 

 muscles rapidly become atrophied, and the reaction of degenera- 

 tion is present. 



If the injury occurs above the level of the spinal centres for the 

 bladder and rectum (L. i and 2), voluntary control over these 



34 



