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  Fitness > Sports Injuries >  << Previous|Next >>

Knee Injuries

The knee is not simply a hinge-joint: you bend and straighten it, but you can also turn it slightly in a twisting movement, when the knee is bent. This rotary movement automatically accompanies the bending and straightening movements. As you bend your knee, the shin-bone turns inwards slightly relative to the thigh bone. As you straighten, the shin-bone rotates outwards. You can only rotate the knee actively and voluntarily when the knee is bent. When you bend your knee against gravity or a resistance, the muscles at the back of the knee contracts to perform the movement. The hamstrings do the main work of bending the knee, but the gastrocnemius tendons help, especially if the movement takes place against a strong resistance. When you straighten your knee in the direction of gravity, for instance while you are lying on your stomach, the hamstrings pay out to control the movement. The quadriceps muscles on the front of the thigh straighten your knee against gravity or a resistance, but they also act to control the movement, when the knee bends in the direction of gravity's influence.

The structure of the knee-joint has two effects. Firstly, the knee is a very stable joint, by virtue of its strong binding ligaments and the protective effect of the muscles which control the joint's movements. Secondly, the joint has quite a wide freedom of movement, because the bones are not closely bound within their own configuration. The knee is one of the three major joints in the leg which transmit loading forces between one's body and the ground. Its stability helps to keep us upright on our feet when we are standing, walking, hopping or jumping.

Knee Pain
This can arise from various causes. The knee can be affected by a spontaneous inflammatory arthritis. Or it can be one of many joints involved in a multiple inflammatory arthritis. Pain referred from the hip or back may be felt as a simple knee pain. Problems in the thigh-bone may causes knee pain. In older age, the knee, like the hip, may be affected by osteoarthritis, or wear- and-tear degeneration. In children, unexplained knee pain can be a sign of a very serious hip condition, the slipped epiphysis.

Knee Swelling
Joint swelling is an important symptom in knee conditions. Because of the complex and extensive synovial lining in the knee, the joint may distend alarmingly, with swelling right round the joint, reaching about seven centimetres above the knee onto the front of the thigh. However, it can also be more subtle. You may also see a small pocket of swelling, perhaps on one or the other side of the joint; or there may be just a slight puffiness on the front of the joint, on either side of the knee-cap. Swelling may occur at the back of the joint, without any visible signs of it at the front. Joint swelling always indicates inflammation. As in the ankle, knee swelling can be caused by gravity bringing the fluid down from some higher tissues: the swelling may track down from the hip joint or some part of the thigh muscles. However, unlike the situation in the ankle, if you have persistent swelling in the knee, which delineates the joint's shape, it is unlikely to be gravitational swelling, and it is very likely to mean that there is something wrong inside your knee.

If the swelling has appeared for no obvious reason, it may indicate that you have an inflammatory or degenerative condition. Your doctor will probably arrange blood tests and X-rays, to decide whether this is so. If the swelling occurs as the result of an injury to the knee, and you are aware of having wrenched it, or fallen on the joint, it is likely that you have damaged one or more of the knee's internal structures, with irritation or damage to the synovial lining. The swelling may come on at the moment of injury, or some hours afterwards.

The knee is very prone to injury, because of its mobility and the variety of stresses we subject it to. The most common type of traumatic injury to the knee is the twisting or wrenching injury. This happens most frequently when your knee is bent, while carrying your body-weight, and you twist awkwardly or unexpectedly. Skiers and footballers are most susceptible to this type of injury, but it can happen to you while walking or running, if you trip and catch your foot, or fall while turning. Any of the knee's structures may be damaged in this type of injury. The full extent of the damage may be impossible to assess immediately after the injury, and may only become evident when the knee subsequently fails to recover its full function.

Damage Inside the Knee
Any of the knee's internal tissues can be damaged by a severe injury, but the cartilage (menisci) and the cruciate ligaments are those most commonly harmed in sportsmen.

1)  Cartilage tears
The knee's soft-tissue cartilages can be damaged by pressure from the bones of the joint when an abnormal force twists the bones against each other unusually. In the normal way, the cartilages move slightly, backwards and forwards, during knee movements. In this way, the cartilages act as buffers throughout the whole movement, although the joint surface of the thigh-bone is bigger than the receiving surface on the shin-bone. However, with abnormal pressure, the cartilages may be jammed between the two bones: if the bones then twist on each other and apply a shearing stress on the cartilage, the tissue splits.

The most common cause is an abnormal twist in your knee while your weight is on the leg. In each case, your knee is bent at the moment of injury. A sudden stress with the knee bent, even when you are not standing on the leg, can be enough to tear the cartilage. Cartilage tears can also be caused by a sudden over- stress when your knee is straight, for instance if you miss a drop-kick in rugby.

This injury gives instant pain, to the extent that you may not be able to move the knee at all, let alone take weight through your leg. Immediate swelling will inhibit movement further, although the swelling may not appear until some hours later, in which case the knee will feel weak rather than stiff in the first instance. Visible swelling may extend right round the knee, making the joint look bloated, or it may be only a small patch, barely visible over the line of the joint. At the moment of injury, it is impossible to tell, from the outside, exactly how much damage has been done. First-aid for the swollen knee must be applied. (see "treatment of acute sports injury").

The only external sign that you might have torn a cartilage is the so-called 'locked' knee. More often, the knee is too painful to move immediately, and this 'locking' feeling only becomes evident when the knee has recovered enough for you to be moving it. Once you have applied first-aid measures and made the knee comfortable, you must be taken for specialist help as quickly as possible.

Once a specialist has diagnosed a cartilage tear in the knee, there are two possible courses of action. Either the torn part of the cartilage must be removed surgically, or the problem must be treated with rehabilitation only. The one certainty is that the torn cartilage will not heal, or mend itself, naturally. If the specialist decides on immediate surgery, it is because he deems that the torn cartilage will create functional problems in the knee.

The cartilage removal operation is called a meniscectomy. Recovery from the surgery can take a varying time, according to individual circumstances. It is possible to be back to full sporting activities within two weeks of removal of the cartilage through the arthroscope.

If a specialist decides not to remove the torn cartilage, after diagnosing the tear, it is because he believes that the damage is slight, and the knee can recover functionally without any need for surgery. Your leg may be immobilized in plaster, to protect the knee, if the injury was severe; or you may simply be given a supporting bandage to control the swelling.

2)  Cruciate Ligament Tears
The cruciate ligaments are two strong bands which bind the shin- bone to the thigh-bone, across the centre of the knee. It takes a strong force to damage them; they can be torn in a severe twisting injury, for instance in a blocked kick or a sliding fall in a tackle during football; or by excessive pressure forcing the knee to 'bend backwards' when it is straight, for instance if an opponent falls across your extended leg in rugby or hockey.

A major shearing force can tear both cruciates together, usually tearing one or both of the cartilages at the same time. A moderate injury may tear one of the cruciates completely, without damaging the second, and with or without accompanying cartilage damage. At the moment of injury, it is totally impossible to assess the extent of the internal damage through outward signs. The only certainty is that, if your knee has swollen painfully, some of its internal structures have been damaged. If you do not have an accurate diagnosis at the time of injury, it may only become apparent that the cruciate ligaments have been damaged much later when you have started doing sport again. Then you may find that in certain positions your knee feels loose and unstable. It may feel as though it is 'rolling' on itself, backwards or forwards, usually giving a 'clunking' sound, with a sharp pain. This makes running and turning difficult. This unstable feeling is an external indication that there is some damage to the cruciates. If your knee locks as well, then there is also likely to be cartilage damage.

At the moment of injury, the knee should be made comfortable in applying the first-aid measures for the swollen knee. It is essential to obtain a specialist opinion as quickly as possible. If the surgeon finds that both cruciate ligaments are completely torn, he will probably perform an immediate operation to try to repair the damage. If there is partial damage to one or both of the cruciates, the surgeon will choose whether to operate, or whether to allow the knee to recover enough for you to resume sport, and see whether there is any residual disability when you use the knee.

Whether the repair is done straight away, or after residual disability has shown up, there are various methods which the surgeon may choose to mend the damage. Some procedures involve mending the cruciates themselves, either by re-attaching a torn end to the bone from which it has snapped off, or by replacing the whole ligament with a synthetic substance. Other methods of stabilizing the knee involve tightening up the capsule and tissues around the joint, to compensate for the internal instability. Whichever method the surgeon chooses, rehabilitation is a slow process; full recovery may take up to a year. It is vital to follow the surgeon's rehabilitation program to the letter, as recovery phases differ according to the particular operation done.

Reference Source 91

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