The Knee Joint - Part Two

By Jonathan Blood Smyth

The locking position close to full extension of the knee is a small internal movement of the joint involving an inward twisting of the thigh bone, a small joint motion but crucial to knee function and illustrating the knee is much more than a normal hinge. The knee has unobtrusive movements which occur within the joint and because these are minor the knee loses significant function if any of this ability is lost. The small movements of joint slide and joint glide are known as accessory movements, occurring during normal joint motion but incapable of isolated performance.

The knee's function is to complete two contradictory demands, the ability to move the body quickly into a newly desired position and the ability to keep the body stable and controlled in a chosen position. In the walking cycle the knee has to be a mobile limb for moving into the next position at one moment then at the next function as a reliably stable support. In the gait cycle the knees go through a repeated process of unlocking to move and locking to bear weight, permitting a human to walk significant distances with safety and effectiveness. Loss of the accessory movements may be involved in early knee problems.

The knee has very strong muscles but can also respond to changes such as an uneven surface by finer controlled reactions. The knee is strong enough to achieve full squatting and then stand our body weight up again without pause. The knee's accessory movements are small in distance with side to side more limited than front to back, both however contributing to coping with uneven ground. The inside of the knee joint can gap open more than the outside due to the natural angle of the lower leg to the knee.

As reviewed in the article which precedes this one, the knee functions typically only in one plane, that of forwards and backwards. If a sideways stress is introduced so movement occurs in another plane also, as with knock-knee or bow leg, the patello-femoral joint and the knee compartments can suffers degenerative consequences. The compartments of the knee are the division into the outside half and the inside half of the joint, with each consisting of a tibial and femoral condyle, a meniscus and the ligament. The amount of sideways angulation alters the way that stresses pass across the knee compartments.

If a degree of bow leg develops in the knee the pull of the quadriceps on the kneecap tends to bowstring it inwards to some extent, making the kneecap grate against the inner side of the femoral groove, potentially causing pain. This also forces increased stresses onto the lateral compartment of the knee, increasing the degenerative processes on that side of the joint. Slight knock knee is more common, and this predisposes the person to lateral kneecap pain and degenerative changes in the medial compartment of the knee.

A lack of the ability to extend the knee completely can also lead to patellar pain, as the residual bend of the knee requires the quadriceps muscle to keep the knee held against gravity, forcing the patella against the femoral groove. Over time these increased forces can lead to the development of anterior knee pain, a very common presentation. As treatment a small heel wedge can be placed under the outer side of the heel, correcting the line of forces through the leg from below and so changing the forces going through the knee.

The patella can also give problems in response to abnormal changes in other joints. As we get older our foot arches can become less strong and so less pronounced, sometimes leading towards a degree of flat foot. As the feet rotate inwards on weight bearing the whole foot and shin move inwards to some extent, introducing an amount of knock knee effect at the knee. This can cause the kneecap to glide more outwards along the groove than normal and lead to patello-femoral pain. An effective treatment can be to wear orthotics in the shoes, which can combine restoration of the foot arches with the necessary level of medial wedging of the heel. - 32188

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