CONTENTS
The name comes from the redness. It is a body reaction, a reflex, a response of the body to infection, trauma, and burns, in fact to any harm. In trauma it is the basis for repair, in infection it is part of the defence mechanism.
It is remembered as having Calor, Rubor & Dolor; also Tumor. Those Latin words mean Heat, Redness & Pain; also Swelling. It is not immediate, taking up to 12 hours to develop; it may increase for up to 5 days; and it may take 3 to 5 weeks to subside. If an injury should swell immediately, that swelling is usually bleeding. But swelling that only comes up by the next day is from inflammation.
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SWITCHES FOR INFLAMMATION AND THEIR RESULTS
Inflammation is one of our basic responses. we do not control it, it happens like a reflex. It is switched on by specific parts of the process of an injury or infection. Here we shall only talk of injury. When tissues are damaged, some of them die because their blood supply is cut off; the torn blood vessels will release blood into the tissues (blood is usually confined inside a blood vessel). Dead tissues and free blood cause the release of chemicals (such as lysozymes). These chemical have several efects:
(i) They make the incoming tiny arterial capillary blood vessels widen, so that blood flow to the damaged area is increased.
(ii) They cause the walls of the capillary vessels to leak, and what leaks out is inflammatory fluid (inflammatory exudate), a specialised fluid with certain cells in it.
(iii) The capillaries are stimulated to grow and reproduce, forming loops of new capillary blood vessels. These grow into the damaged area (attracted by the chemicals released by the injury), which otherwise would be an unoxygenated place - a no-go area for living cells.
(iv) Local fibrocyte cells in the tissues are switched on to reproduce and lay down new scar tissue.
(v) These chemicals, with others, are probably one of the causes of pain.
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The process of inflammation always produces swelling; that swelling is the inflammatory exudate (L. = come out of). It comes out of the capillary blood vessels when they have been caused to leak by the chemicals released by injury. It is a fluid derived from the plasma, and it contains all the defence mechanisms:
(i) Antibodies, complement etc. They are proteins that immobilise bacteria
(ii) White cells - that is polymorphs (poly Gk=many, morph Gk.=shapes), which attack and may engulf bacteria; and macrophages (macro Gk.=big, phage Gk.=eater), which engulf and digest damaged tissues and dead bacteria.
(iii) Fibrinogen, a normally present plasma protein which gets changed to fibrin by those chemicals, thus making fibrous scar tissue. If, with a joint injury, there is a large swelling (which will be blood plus inflammatory fluid), it will often leave behind (when it has finished repairing) a slightly swollen area of scar, that persists for many years. If there has been a big injury, or repeated minor injuries to a part, the scarring from the fibrin in inflammatory exudate will persist. Even long after the trauma the body never lets you forget it - the scar may form lumps and bumps that may be felt through the skin.
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Inflamation continues as long as either infection or damage is present. It is familiar to us all as the redness surrounding a cut or a bruise. Major injuries remain swollen for ever, puffed up by all the scar tissue laid down (fibrin). But fibrin also causes stiffness, and is The Enemy in sports physiotherapy.
If an injury produces a collection of free blood, no cell can live in the middle of that blood, where there is no oxygen. Free blood can only be cleared by cells, which can only do their job at the margins, where there is oxygen. So it is cleared very slowly, sometimes taking months.
It is just the same with a collection of pus - pus should be allowed to come out. Once pus is present, antibiotics will not work - there are no blood vessels to carry antibiotics into pus.
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(i) Rest: The commonest cause of failure to improve is failure to rest.
(ii) Elevate: Makes the bleeding less, decreases exudate from capillaries, drains fluid away.
(iii) Compression - only gentle compression! : It helps to prevent inflammatory fluid from gathering.
(iv) Ice or cool-pack: This narrows the capillaries; less bleeding and less exudate. Ice must not be placed directly next to the skin, so wrap it in a cloth.
(v) Gentle movements: Movement will help to pump fluid away; it will also help orientate scar.
The standard recommendation for minor injury is: ICE; COMPRESSION; ELEVATION
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THE SWOLLEN JOINT AFTER INJURY
If a joint swells immediately after an injury, that fluid is blood. If the joint swells quickly after an injury, that must mean a rapid bleed, which means that something with a big blood supply has been injured. Things with big blood supply are - either bone or muscle, or possibly a substantial ligament.
If it swells up in two, four or six hours, that is also blood; but as it has bled not so fast, it means either fewer vessels or a smaller blood vessel.
But a joint injured one day and swollen the next day (and not earlier) has inflammatory exudate in it.
Twist knee, feel pain, hear a pop, swell immediately - that's an anterior cruciate tear. Twist knee, feel pain, couldn't go on, but didn't swell till next morning, that's a sprain or strain of meniscus cartilage or ligaments.
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INFLAMMATION, WHICH PRECEDES REPAIR
From dead and injured tissues, from broken and hurt platelets, come the chemicals that initiate the inflammation reflex, called Bradykinin and Histamine. These chemicals are the switch-on for Inflammation.
The resulting cascade of events is:-
- Local capillaries widen, leak fluid and cells from the blood, and begin to bud off new capillaries that form loops of new vessels that grow into the injured region. The fluid that leaks out is inflammatory exudate.
- Inflammatory exudate contains protein antibodies (non-specific), fibrinogen (a soluble protein) that becomes fibrin, and polymorphs and macrophages - cells that clear up debris and attack invading bacteria.
The SWITCH ON also switches fibrocytes, previously resting in the tissues, to fatten up, get active, reproduce themselves and start making masses of fibrin. This will eventually mature to become scar tissue.
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Macrophages eat debris and bacteria; polymorphs eat small debris and dead bacteria. Fibrocytes fatten up and begin to multiply, and lay down fibrin fibres.
Inflammatory exudate and cells keep on coming while there is dead and injured tissue present that continues to produce the switch-on chemicals. Normally, as time passes and they gradually clear up on the detritus (damaged tissues), the chemical switches gradually decrease. And so you get a gradual decrease of inflammation.
In a small skin cut, visible inflammation is minimal by 10 days, but in a significant joint injury, inflammation can continue for 5 or 10 weeks; even more if there is a large bleed. Activity of fibrocytes contines for for a long while,and as a result the injured area is filled with a matrix or mass of fibrin - like a matted glue of fibre-glass - producing a slightly swollen region.
However, if injury is repeated again and again, fibrin gathers, and the blood passing to local structures may begin to have their blood supply limited, because the tiny capillary vessels are being obstructed by the scar tissue. The limited blood supply can lead to local cell death, and a cycle develops: - Local cell death -> switch-on for Inflammation -> exudate and repair -> maturation of fibrin to scar -> local cell death. The situation becomes difficult to influence.
In time, scar tissue matures. We all know how a cut in the skin is at first pink, but by months later it is pale,or whitish. This is due to the lack of blood supply in mature scar. Also it does not tan in sun - this is because the area of scar has a different make-up from normal skin, which has suntan-producing cells (melanocytes) in the deep tissue. And if the wound is deep and complex, there may be creases around it. These are caused by the scar contracting.
In a muscle, the final result of damage is a dip, the dip being scar in a surround of fat muscle cells. Scar is much less elastic than muscle, so when the whole muscle becomes stretched, the scar cannot move as much as the muscle tissue. Hence it is well-known to athletes and sports-people that following a muscle tear, you must warm up and stretch before any exercise. And even then, the muscle may tear again at the margin of the scar.
Active fibrocytes respond to tension - they align themselves so that the fibrin they produce is roughly parallel with the tension. So after an injury, the more we can put a region through its normal range of movement, during the repair time, the better engineered the resulting fibrin will be. Instead of a mat of disorganised fibres, those wrongly aligned will be broken while those that are correctly aligned will increase and persist. The breaking down of those wrongly aligned strands of sscar tissue may cause sharp pains during the rehabilitation phase - this can be worrying.
Hence the suggestion that joints be taken through their normal range of movement (so far as is possible) during the repair stage. This hould help to align the scar tissue fibrin fibres correctly, so they are not just in a matted scar.
The repair stage is usually reckoned to be six to eight weeks. And if movement is not possible, perhaps due to the need for a cast, for a broken bone for for instance, the nearby joint will be hard pushed to regain its former movement - even if it was not itself damaged.
This is a soft tissue point of view of course! Any clinician dealing with a broken bone will rightly put the need for proper repair of the bone above the need for stretching of scar in the surrounding soft tissue. But where the clogging tentacles of scar tissue in the soft tissue can cause a significant difference to the end result - in terms of what movement is possible - then measures to influence scar tissue are started surprisingly early.
In hand surgery for instance, therapists begin mobilisation and rehabilitation of soft tissue from the third day. And this is the reason that a knee that has been operated on may have a continuous passive motion machine strapped on very early after the operation - it helps to disperse the swelling and give those fibrocytes their orders!
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© Copyright Philip Evans |
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