There's pain
and then there's
%$#@*! Pain
The one thing that everyone on the board wants
to know about is Pain. Why do I have it? how long does it last? will it go away if I do
this or that? what is normal? how do you cope? In response I would like to explain a few
things about pain, how and why we feel it and what is normal and abnormal.
What is pain?
That sounds like an airy fairy philosophical
question but there is actually a very concrete answer. Pain is the sensation mediated by
special nerves called pain fibres. If you stimulate these nerves electrically you get the
sensation of pain even though there is no damage and nothing is permanently painful. The
connection with your brain is interpreted as pain. So anything which makes those nerve
endings fire off is felt as pain. Pain nerves are amongst the smallest in the body and
they conduct impulses slowly. That is why there is an appreciable delay between the impact
of a blow and the feeling of pain. Touch and position sense travel much faster. One of the
other consequences is that pain nerve fibres are easily blocked by pressure and by local
anaesthetics (freezing). If your hand "goes to sleep" the pain fibres are
blocked but you can often feel things touching and moving. Another consequence of their
small size is that pain nerve endings are very sensitive and easily fired off, so we feel
pain when almost anything is wrong. Pain fibres are the first ones to grow back after a
nerve injury so that the first sensation to return to a numb area is guess what!
What is the
function of pain?
Pain is a warning. You might wonder why there is
such an elaborate and pesky system. Some rare individuals have a deficiency that means that they
cannot feel pain. This lack leads to injuries and infections being ignored and getting out
of hand. (see an
account of one young man's problems) So the purpose of pain is to draw attention to a
problem. In nature if an animal is hurt the main way of healing it to keep the injured
part still. So pain alerts one and makes you want to keep everthing immobile - which with
modern treatment may not be the best adaptation. What I am trying to say is that pain and
pain response evolved in a situation where the only treatment was to crawl away
and lick your wounds. Now we normally get medical treatment for severely injured legs and
recovery from the injury may be faster and better if you move the limb early. So while
pain is still an indication that there is something wrong, our innate response to it may
not always be appropriate.
Why does it hurt
when you break a leg?
As we saw in the previous paragraph the
"purpose" of pain is to warn that something is wrong and to enforce rest. The mechanism
of pain is another issue. Nerves large and small run in all the tissues of the body
including bones, muscles, ligaments and tendons. When you break something you break the
nerves which are in that tissue. The ruptured nerve endings are extremely sensitive and
the pain fibres are the most easily stimulated. Any time you move the injured area or
contract muscles which compress it, the "raw" nerve endings fire off - ouch!
Sometimes the broken leg is also distorted and this will stretch the nerve endings. So to
relieve the acute pain from a broken bone, first aid involves straightening and splinting
the limb so that the broken pieces do not move.
"Normal"
pain during healing of a fracture
Once a fracture is set and immobilized the pain
from moving the broken pieces no longer applies. Since OS are bone oriented doctors we
tend to think that because the bone doesn't hurt so much there is no major pain problem.
But of course there is a problem and it comes from many sources.
Movement. Often the fracture fragments are not
completely immobilized. This is especially true in a cast. A cast is designed to keep the
fragments lined up and in the correct position but it cannot prevent micromovement at the
fracture site. This micromovement doesn't prevent healing but it does hurt, by the same
mechanism that the original injury hurt - stimulation of damaged nerve endings.
Soft tissue injury. The force that breaks the
bone and the sharp edges of the broken bone itself will most often cause bruising and
laceration of the muscles, tendons and ligaments in the area. These structures are
not immobilized by the orthopaedic treatment, be it casts, splints or internal fixation.
They too have torn nerve endings and these nerve endings are sensitive.
Surgery. Cutting the skin and muscle over a
fracture in order to expose it so it can be reduced and "fixed" damages the soft
tissue also.
Inflammation. Even if the fracture is immobile
and the soft tissue injury is minimal the area still hurts. This is because inflammation
is the first stage of healing. Inflammation is the process by which the blood supply to
the area is increased to mobilize resources, the dead, injured and non functioning tissue
is removed and the stage is set for new reparative tissue to start growing. Inflammation
is started when histamine is released from damaged cells. This initiates a complex series
of changes including
- Dilatation of blood vessels increasing the overall blood
supply
- Blood vessels become "leaky".
- White blood cells migrate out of the vessels and start mopping
up detritus
- Increased tissue fluid
- New blood vessels grow into the volume occupied by blood clot
and necrotic tissue
- Fibroblasts (cells which lay down collagen fibers) arrive with
the new blood vessels and lay down a collagen matrix (scar)
If you look carefully at all these changes you will realize
they all have one thing in common. They increase the volume of the injured area. In other
words the region swells. This swelling is both inevitable and part of the healing process.
However it hurts. Some parts of the inflammatory process are inherently painful, like
histamine release. Swelling is sore because it puts pressure on the damaged nerve endings
and makes them fire off.
- Circulatory changes. The increased supply of blood is normal
but the problem of swelling is often increased by damage to the drainage system of the
limb. The veins and lymphatics that take fluid away from the limb are often injured so
there is no way for the blood and tissue fluid to be drained away. This compounds the
problem of swelling.
- Loss of the muscle pump. The big veins of the leg have valves
in them to allow blood to move up the leg but not back down again. When the muscles
contract the veins are flattened and blood is pumped towards the heart. When the muscles
are immobilized by pain this mechanism doesn't work and the limb swells even more.
- Bruising. Tissues that weren't injured may be affected by
bleeding from the injury that tracks away from the fracture and bathes tendons and
ligaments in blood. The blood coagulates and an inflammatory process is set up to clear
away the blood clot. This may be quite remote from the original injury.
So during the inflammatory period of healing which lasts for
2-3 weeks following injury much of the pain is related to swelling and measures to relieve
swelling are the most effective ways to manage pain. These include elevation, ice, gentle
movment of the uninjured muscles and gentle massage to improve the circulation. Wheras in
nature, movement is a bad idea because the fracture will be moved, after immobilization of
the fracture movement is a good idea because it improves the circulation, nourishes the
joints and prevents the tissues from scarring and sticking together.
The acute inflammation settles within a few weeks and the
scar tissue transforms itself into bone in the area of the fracture. During this period
scar also develops wherever there has been bleeding or bruising. Scar tissue tends to bind
tendons and ligaments together so that they do not glide normally. As normal function
returns to the joints and the muscles start to move again the scar tissue has to stretch
and this hurts and may even provoke a return of swelling.
The Short and the
Long of it
The best news is that the pain due to fracture
movement and to inflammation is shortlived. Fractures stick together and the inflammatory
process settles down within 2-3 weeks depending on the severity of the injury and the way
it has been treated. However, the remaining healing processes are also uncomfortable -
remodelling of scar and bone tissue, stretching of scar to allow full movement, recovery
of muscle strength and function are all uncomfortable to some degree. Stretching of scar
tissue can be severely painful. These processes go on for up to 18 months after an
uncomplicated normal injury. The feeling that your leg isn't normal may last that long -
even if it is headed back to normality.
Abnormal pain
to be continued
This topic is complicated, difficult, sometimes
emotional and very personal. Your comments and embellishments would be most welcome and
likely to add a lot to this somewhat dry and detached account!
Myles
Clough MD OS Posted 5/1/02 |
