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Workings Of The Knee
As our knees come towards straight in order to weight bear the quadriceps comes into action to straighten the leg towards full extension, engaging the locking position of the knee. One of the characteristics of the human knee is that it ensures efficient and safe weight bearing when standing along with very low energy requirements, unlike the knees of apes. As the knee approaches fully straight the inside part of the quadriceps muscle helps the joint swivel inwards into the locked position. When we stand with our knees straight, we can remain in that position with no activity in the quadriceps and so with very low energy output. Inside the joint are two crescent-shaped structures made of cartilage, looking a little like banked tracks, accommodating the large rounded femoral condyles. Their exact function is not clear but they may contribute to guiding the knee towards locking, stabilise the knee by centring the condyles during bending and straightening and evening out any potential unwanted small movements during joint motion. The kneecap is the other part of the knee joint and is a small bone with an inner lining of articular cartilage which is suspended in front of the knee joint. The kneecap or patella is placed within the tendon the main thigh muscle or quadriceps, the muscle which enables us to move our body weight up and down stairs and up from a chair. The patella is shaped on its inner surface with two facets, fitting into the groove formed between the condyles of the femur, sliding along the groove as the knee moves. The kneecap is present to allow the muscular forces developed by the quadriceps to be amplified across the knee and so enable application of high levels of power. The knee is designed to move effectively in a flexion and extension direction and this alignment prevents mechanical problems developing. If a sideways pressure is applied to the knee continually by abnormal posture such as bow leg and knock knee then a painful functional condition can develop. Abnormal forces cause joint compression as the forces are thrown onto one side of the joint and increase the friction and wear. The kneecap can also suffer from misalignment as it glides on one side, causing pain by the increased friction against the side of the groove. The patella and the internal cartilages (also known as menisci) take a lot of force during knee movements and many problem conditions are related to these structures. The knee joint's range of movement is typically from zero degrees (straight) to around 140 degrees, although this does vary with general joint mobility and with body weight. During flexion and extension of the knee the femoral condyles slide and glide on the tibial condyles, which themselves slide backwards and forwards. The gliding of the tibia backwards and forwards makes certain that the femoral condyles will not slide off the tibia during movement. During knee motion one of the bones moves in relation to the other one, in the sense that the movement of one is occurring over the other which is also moving in a complementary pattern. This allows a much greater range of movement than would otherwise be possible. There is a degree of rotation of the femur which occurs at the knee joint and this is obvious as the knee approaches full extension and the femur turns in slightly to achieve the knee lock. Article Directory: http://www.articledashboard.com Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in Edinburgh. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK. |
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