Bruising is due to bleeding. Blood from injured blood vessels and soft
tissue spreads out under the skin and may track a long distance from the fracture site.
For example it is common for people who have a break near the knee to see bruising coming
out behind the ankle. The big muscles of the calf direct the blood down; it can't come
directly to the surface near the knee. sprains of the ankle often result in bruising
tracking down to the toes.The amount of bruising that you see under the skin depends on
many different things. Obviously the amount that you bled, but also the looseness of the
tissue, the tightness of any splints, bandages or casts and how much you had the leg hang
down. The amount of visible bruising is not necessarily a guide to how bad the soft tissue
injury was. There is a big vein under the skin at the ankle (the saphenous vein). If you
disrupt that you will have massive bruising even if the rest of the soft tissue injury was
relatively minor.
Once the injury stops bleeding the blood clots and the red blood cells die; then the
iron containing blood pigment, haemoglobin, escapes from the cells. This pigment is red
when it contains oxygen but is a dark purple when it is depleted of oxygen. This depletion
happens very quickly after the blood clots, so bruising is "black and blue". The
inflammatory cells which start mopping up the dead tissue, further denature the pigment so
that it can turn yellow and green. Eventually as the blood clot is reabsorbed and
converted to scar tissue the pigment is also reabsorbed. However, when there has been a
large amount of bruising the skin may be stained permanently. It can take up to 18 months
for the colour to return to normal.
Where there has been a lot of bruising there is likely to be a lot of scar tissue and
you need to take care to avoid adhesions. Stretching the joints and recovering full
movement of the muscles and tendons is the best way to avoid a problem. This is of more
importance than the staining.
Myles Clough MD OS
