The Knee Joint-Part 2

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 is very powerful but also capable of very fine movements in response to changes such as uneven ground. It has the power to allow us to squat down and stand up again without missing a beat. Side to side accessory movement in the knee is limited to a small range but this may help with adapting to an uneven surface, with a gapping of the inside of the knee joint the larger of the two movements due to the natural outward angulation of the lower limb and the weaker ligamentous support.

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.

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.

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.