Sometimes patients will injure or tear their meniscus cartilages. I explain to patients that their meniscus cartilages are more or less hooked together to form a ring within the knee. When we step down these discs expand or stretch out to help absorb the stress or shock. Functionally the medial and lateral meniscus work together like a hoop around a barrel. As water is placed into the barrel the hoop works to distribute the stress and hold the barrel together. This analogy is very important as I also explain to patients as well as when teaching to others about the topic that not all meniscus tears are created equal. Some simply tear though a portion of the meniscus where others break or sever the meniscus in half. Those that injure just a portion of the meniscus are functionally like thinning out the barrel hoop. The hoop is somewhat weaker and thinner but the circle of the hoop is intact and the function remains the same. In those tears where the meniscus is completely torn through these are like cutting or breaking the hoop. Once the hoop is broken it does not matter if a small sliver is cut thru the hoop or a large segment is removed. In either case the hoop no longer functions to hold the barrel together and all function is lost.
Meniscus tears can be caused by injuries—slips, falls, twisting, etc. and sometimes they develop without recognized or identifiable cause. Tears that occur without a specific injury are much more likely to occur in patients over the age of 40 and are likely “degenerative” in nature. By describing these tears as “degenerative” it means that the tears have occurred in a meniscus that is weakened by age. In this case a weakened meniscus tears even when subjected to what we would consider a normal stress such as walking or climbing up stairs. These meniscus tears typically occur in knees that have some degree of wear to the articular cartilage of the knee. Stated another way patients with these tears over that occur without injury almost always have some associated arthritis. Associated arthritis definitely becomes more common the older the patient is at the time of diagnosis.