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The Knee Joint – Part Two
The inward rotation of the femur which occurs as the knee comes close to its locking position of extension is not large but very important to knee function, making the knee much more complex than a simple hinge joint. The small internal movements of the knee are limited in the knee joint and the joint cannot afford any losses of these motions without losing some of its function. These small movements are called accessory movements and are small gliding and sliding movements which occur within the joint during functional activity but which cannot be performed in isolation.
The knee is subject to conflicting demands for both mobility and stability, needing to perform as a strong and predictable support and also to function to provide mobility very quickly. In the example of gait the knee has at one point to stabilise the body under its whole weight and next release the stability and move forward as a mobile segment. Walking then consists of a cycle of the knees locking to bear weight and then unlocking with predictable regularity, allowing a person to walk rapidly and make considerable progress without falling. As a knee gives early problems this may involve the loss of accessory movements.
The knee is controlled by very powerful musculature and can perform fine coordinated actions as well as power movements. We can do a full knee bend and then get right up again without any delay in the movement. The amplitude of the accessory knee movements is not large but may be useful in managing uneven surfaces. The medial side of the knee gaps more significantly under stress as the medial ligament is looser than the lateral and the slight natural knock knee alignment tends to stress the knee that way.
The first article about the knee covered the idea that the knee moves backwards and forwards and tends to stick in that plane, so if an abnormal stress such as to the side is added this changes the balance in the joint. The kneecap and the main knee compartments can experience wear changes if the knee suffers from bow-leg or knock knee. The knee is divided into two compartments, the medial and the lateral side, both with their own meniscus, ligament, femoral and tibial condyles. The stresses which are transmitted across the compartments vary with changes in the sideways angle of the knee.
The development of an amount of bow leg at the knee changes the quadriceps pull so the kneecap is pulled to the inside, pushing it more forcefully against the inner edge of the groove it sits in, which can result in a painful condition. Along with this there are increased loads on the lateral compartment and this can hasten degenerative changes on that side. Normal knee joints naturally have some knock knee but if this amount is increased then the outside of the kneecap is likely to suffer from impingement pain.
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 suffer as a consequence of changes which occur in other joints nearby. The arches of the feet can weaken from bearing our weight for many years, losing strength and collapsing to some degree towards flat foot. When the foot bears weight the arch collapses inwards and takes the ankle and the lower leg with it, increasing the degree of knock knee. This can predispose towards anterior knee pain as the patella is forced medially against the femur. Corrective orthotics to be worn in the shoes can be a useful treatment, allowing heel correction as well as support for the arches in weight bearing.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and Physiotherapists in Coventry. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
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Comments on The Knee Joint – Part Two
The knee joint is one of the most important joints in the body. There would be no walking without it! Thanks for sharing.