The Human Knee – Part Two
As the knee approaches the position where it is going to lock the femur rotates inwards, a movement which is only small but vital to the normal function of the knee, indicating its great complexity beyond a simple hinge. The minor movements which occur internally in the joint are restricted in the knee and it cannot manage to lose any of these small motions without functional loss as a consequence. Accessory movements are the name given to these limited gliding and sliding movements which normally occur during activity but which can’t be done on their own.
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 mentioned in the preceding article, the knee mainly functions in one plane, that of backwards and forwards movement. If it is forced to move in a different plane, such as in the presence of bow leg or knock knee, there will be consequences in terms of degenerative changes in the knee compartments and in the patello-femoral joint. The knee compartments refer to the inner and outer halves of the knee, the medial and lateral compartments, each with its femoral and tibial condyle, ligament and meniscus. Alterations in the sideways angle of the knee joint changes the forces which pass through the 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.
Difficulties with other joints can cause changes in the patella stresses also. The arches of the foot suffer from time and body weight and so reduce as they get weaker, moving towards a flatter foot. On weight bearing the foot turns inward as it flattens, bringing the ankle and the shin towards the centre with it, exaggerating any knock knee amount. Patello-femoral pain can then occur as the kneecap is pressed more forcefully towards the lateral side of the knee. Prescribing individual orthotics for the shoes can be an effective management, both providing an amount of medial heel wedging plus correcting the collapse of the foot arches.
Jonathan Blood Smyth is the Superintendent of Physiotherapists at an NHS hospital in the South-West of the UK. He writes articles about back pain, neck pain, and injury management. If you are looking for physiotherapists in Brighton visit his website.
Article source:Slim Index