09 Nov 09 The Knee Joint
The knee, like the elbow to some extent, is a hinge joint but not a simple one. The lower part of the thigh bone expands into the femoral condyles and the upper shin bone likewise expands into the tibial condyles, the junction of these two enlarged areas forming the knee joint. The small bone on the outside of the knee, known as the fibula, is not involved in weight bearing nor is actually part of the knee joint, serving only as an attachment area for the muscles controlling the ankle, foot and toes. The knee functions as a hinge dividing the leg, allowing the exertion of high levels of muscular propulsive force, the folding of the leg in bending and the shortening of the leg in stepping to allow efficient gait.
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.
With the joint itself are the menisci, cartilaginous structures in a crescent-like structure rather like a banked track, fitting the rounded femoral condyles. It is not entirely clear what their function is but they may help make the knee more stable by keeping the condyles centred during movement, restraining small unhelpful movements as the joint moves and guiding the knee towards the effective position for locking. The patella or knee cap is the third part of of the knee joint and this small bone has its underneath lined with joint cartilage and is held in front of the knee.
The patella or kneecap is situated in the tendon of the quadriceps muscle which is the major muscle at the front of thigh and responsible for pushing us up from sitting and up and down stairs. The joint surface of the patella fits into the large groove between the front of the femoral condyles, sliding up and down the groove as the knee bends and straightens. The function of the patella appears to be to magnify the power of the quadriceps muscle and so improve its ability to exert the very large forces needed to move the body weight.
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.
It is in order to stop the femoral condyles slipping off the back of the tibial plateau that they perform the internal glide in a back and front direction. One bone does not move on its own as the joint changes its position, but rather both move in a complicated fashion on each other to allow the functionally desired movement to be achieved. A much more extensive range of motion is achievable with this design. Rotation also occurs at the knee joint but is less obvious, becoming more apparent as the knee extends more closely to the locking position and the internal rotation of the femur occurs.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in Sheffield. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
Tags: alternative medicine, back injury, back pain, back pain relief, Frozen Shoulder, health, Health & Fitness, injury management, pain management, physical fitness, physiotherapists, physiotherapy, Piriformis Syndrome, sciatica
