The Knee Joint – Part Two

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 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 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.

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.

If the knee is not capable of full extension then the kneecap can develop problems due to the persistent flexion which makes the quadriceps overactive to hold the knee in place, increasing patellar compression. This increased compression can cause a very common condition known as anterior knee pain or patellofemoral pain. To correct the lateral misalignment a small wedge can be placed under the outer edge of the heel to correct alignment of the shin and so influence the stresses which are passing through the knee joint above.

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, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in Leicester. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.