The Knee Joint - Part Four

By Jonathan Blood Smyth

The menisci (often called cartilages) and the main joint surfaces of the knee can be made more vulnerable to injury and damage if knee control is not good enough to prevent unplanned joint movements. Meniscal function is partly to control movement of the femoral condyles into particular paths, centring them on the upper shin bone plateau. Without the guiding help the large and strong condyles can catch the edges of the menisci as they roll across the tibial plateau and so cause tears or other damage to the menisci.

Damage to the menisci can take many different patterns, including splitting, tearing and losing pieces of the edge. A split can develop along the circumference of the meniscus while both ends remain attached, a so called "bucket handle tear". Part of the meniscus can become detached in a damaging manoeuvre such as twisting and become a loose body, moving about inside the joint and jamming between the joint surfaces at times. When this occurs during weight bearing then the knee can give way, and it can make the knee difficult to straighten. The cartilage cannot heal as such as the blood supply is very poor.

As the cartilage continues to erode it can guide the femoral condyles less and less, perhaps increasing the forces which are transmitted across from the femoral condyles to the tibial surface. As the surfaces suffer increased forces they can also degenerate, leading the osteoarthritic changes within the knee. Before modern arthroscopic management a common procedure was to remove the meniscus entirely if it was giving trouble, leading to osteoarthritic changes some years later. Any significant problem with a knee leads to wasting of the medial part of the quadriceps muscle and much effort is expended in strengthening this area.

However, strengthening of the medial lower quadriceps will not be very effective if no attention is paid to the knee's range of motion and its accessory movements. Restoring the accessory movements can help the knee's overall function and if full extension is restored then the function of the medial quadriceps muscle will gradually return towards normal naturally. Without full extension then no amount of exercise will restore the muscle function. Modern arthroscopic operative techniques involve slim probes to view the interior of the knee, and the minimum is done internally to remove the troublesome parts, leaving the vast majority of structures intact.

The most common joint degenerative disease is the world is osteoarthritis, affecting many hundreds of millions of people and almost universally prevalent in old people to some extent. The likelihood of developing osteoarthritis is increased if there has been meniscal surgery, ligament or joint damage or a history in the family. With damage to the cruciate, medial or lateral ligaments there may be excessive internal joint movement which can lead to abnormally high joint forces and consequent joint surface degeneration. There can be high levels of force generated by the shearing forces acting laterally across a joint.

As the knee ages it can start to grate or click on certain movements and is only usually problematic if it is kept still for a long time in one position. The capsule of the joint can tighten if we don't go through the strong activities which push the joints to the ends of our ranges like we did when we were younger. Joint compression can increase and stress the joint surfaces and make an injury more likely due to the tightness. Gradual wear of the cartilage continues and the bone underlying the cartilage, usually with some degree of pliability, develops increased hardness and density, called sclerosis.

An arthritic knee can be enlarged, swollen, hot and painful with limited range of movement, crepitus on motion and a degree of disability. Pain and swelling can go through repeated cycles and gradually become worse as the joint deteriorates. Walking may be limited and the knee pain can disturb sleep due to the difficult in maintaining a position. As the inside of the joint can become very tender it does not tolerate pressure from another knee or the gapping pressure which can occur when we lie on our sides. A pillow between the knees is typically required. - 32188

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