In Rhodesia many heavy sacks are carried on porters' heads, yet back injuries are infrequent, only 14 cases having been seen in 10 years. Unlike most neck injuries these affect the upper rather than the lower cervical regions, and it is thought that the forces at work are more rotational than flexional.

X-ray studies show that when loaded with a 200-lb. (90.7 kg.) sack the normal cervical spine assumes a vertical position and the discs become compressed. Forward angulation occurs where the discs are weak, and may predispose to injury either at that level or in the region of compensatory hyperextension above.

The prognosis in the neck injuries largely depends on the level affected-the higher the injury the better the prognosis. This is probably because the cross-sectional area of the spinal canal is larger in the upper cervical regions, thus allowing more movement of vertebrae before the cord is involved, while the fractured vertebrae themselves show less bony displacement than when the lower levels are involved.