F- CLINICAL ASPECTS OF SPINAL CORD INJURIES
487
—i.e. the distance of bony weight-bearing prominences from the skin and the thickness
of padding tissues such as fat and muscles between bone and skin.
The fourth intrinsic factor is the spasticity of the paralysed lower limbs, especially
adductor spasms, which is responsible for the development of sores on the inner surface
of knees and inner ankles as a result of producing shearing stress to the covering skin
by continuous rubbing.
B. EXTRINSIC FACTORS
There are three extrinsic factors: pressure, maceration from exposing the skin to moisture
(urine) and cold. Of these, pressure is of decisive importance, because causing blockage
of the vascular supply represents the immediate cause in the development of sores. The
degree and extent of the harmful effect of local pressure in paraplegia causing ischaemia
of skin and deeper tissues are determined by its intensity, duration and direction. As to
the direction, one must distinguish between purely vertical pressure and shear-stress,
of which the effect of shear-stress is much more disastrous for its cuts of larger areas
from their vascular supply. There can be little doubt that the forces resulting from shear-
stress, acting parallel to the surface of skin and sliding the upper layers relative to the
lower, play an essential role in determining the shape and size of a sore. In this connec
tion, the disastrous effect of plaster casts and, in particular, plaster beds has already been
mentioned.
With regard to the duration of pressure in producing death of tissues, Trumble
(1930) found that a pressure of more than
i\
Ib per in2 (about 80 mmHg) over a long
period is likely to cause death of tissues.
Maceration of the skin by allowing the incontinent patient to lie in a wet bed may
play an additional part in early decomposition and gangrene of the tissues once ischaemia
due to pressure has developed.
Cold in later stages of paraplegia may facilitate the development of a sore due to
vasoconstriction in the paralysed limbs.
Classification and localization
While pressure sores can develop in any part of the body which is exposed long enough
to local pressure, in paraplegics one can distinguish between predilection places of sore
development in the early stages and those in the late stages of paraplegia. The areas
involved, as a rule, in the immediate and early stages are the sacrum (Fig. 195), trochan-
terics, ischium (Fig. 196), knees (Fig. 197), head of fibula (Fig. 135), heels and toes
(Fig. 198) and, in patients lying on plaster beds or casts, also the spinous processes, ribs,
and anterior and posterior superior iliac crests. Moreover, in patients placed in plaster,
sores may develop at the edge of the plaster, even in the sensitive area, which of course are
painful.
In later stages of spinal paraplegia, one has to distinguish between two groups of
patients: (i) those who remain bedridden, for one reason or another, and (2) mobile
paraplegics either in wheelchairs or walking with crutches and calipers. In the first group,
