Knee arthritis

The knee is the most common joint to be affected by osteo-arthritis (OA). The Australian Orthopaedic Association reports that in 2013 over 480,000 knee replacements were performed in Australia. Total knee replacements have increased by 101% over the previous 10 years. Over 97% of these were for severe knee osteo-arthritis.

Get to know your knee joint

Reflecting the large compressive forces it must withstand, your knee is the largest and most complex joint in your body.  The primary function of your knee is to bear your weight in the upright position, but it’s common for significant destructive forces to quietly attack your knee in the non-upright position.

Your knee actually consists of three joints. Bearing about five sixths of your weight, your tibiofemoral joint is the most common site of knee arthritis. This joint is made up of a widening of your thigh bone (femur) at its lower end and the widening of the upper end of your leg bone (tibia). All of the bone surfaces of your knee are coated with a very thick layer of cartilage of up to six millimetres thick, thicker than any other joint.

To provide even further protection against the large compressive forces acting through your knee, nature has come up with a brilliant solution in the form of two thick shock absorbing cartilage discs called menisci, one in the inside (medial) knee compartment and the other on the outside (lateral) knee compartment.

Your medial meniscus is substantially larger and thicker than your lateral meniscus, reflecting the greater forces acting on the medial knee compartment, and is far more prone to damage by excess loading. Breaking down of this cartilage is a key feature of knee OA.

Prevention and treatment of knee OA is based on an understanding of the primary role of mechanical forces acting on the knee. With fifteen muscles directly acting upon your knee joint, and indirectly by a further seventeen (which move the upper end of the thigh bone at your hip), many of which are the most powerful muscles in your body, they generate the vast majority of the huge compressive forces acting on your knees.

When these muscles are used in balance with other muscles, the forces acting on the knee joint are evenly spread out over the largest possible surface area of the joint with each bit sharing the load. Your knees relish these conditions.

But many people have a propensity to unnecessarily overwork some of these muscles, leading to a relatively small area at the inner (medial) part of the joint taking on the brunt of the load. At the same time other parts of the joint tend to become under-loaded, which can also lead to weakening and breaking down of joint tissue.