Do you understand the difference between an acute meniscus tear and a degenerative meniscus tear? Many clinicians do not. Perhaps this is partly because calling the latter a “tear” is a bit of a misnomer. Let’s dive a bit deeper.
The menisci are C-shaped pieces of fibrocartilage (also known as type-1 cartilage) in the knee. Each knee has two of them, and together they provide a cushion between the distal femur and the proximal tibia. More specifically, the menisci provide shock absorption by distributing the load more evenly. They also make the knee joint surfaces more congruent, because, without the menisci, the rounded femoral heads would sit on top of a flat tibial plateau. By increasing congruency, joint stability is also improved.
Now back to the “tear” part. An acute meniscus tear occurs as the result of a single, traumatic injury. It is exactly what you would picture when thinking of something that is torn – there is a split or divide in the piece of fibrocartilage. Acute meniscus tear often occurs in athletics and cause sudden sharp pain with or without mechanical symptoms like clicking, catching, and locking sensations in the joint. Naturally, these acute tears are usually amenable to surgery. Sometimes the tears are repaired, i.e., put back together with sutures.
Other times the tears are trimmed back to a stable base because it is in a direction that is parallel to the meniscal fibers, so sutures will not hold. Both of these surgical procedures can be performed arthroscopically.
Degenerative “tears” are not seemingly like a tear at all. Imagine having a piece of Styrofoam or a sponge and then taking a piece of sandpaper and abrading the top surface of them. The top surface would become worn down, rough, and frayed, but there would not necessarily be a discrete split or rip through the material. Degenerative meniscus “tears” are just like this. Degenerative meniscus “tears” develop gradually over time in people who have osteoarthritis in the knee. The roughened surface of worn-out femoral articular cartilage in an arthritic knee is what roughens up the top surface of the meniscus below.
Since there is no discrete tear to repair or debride, surgery is not the answer for degenerative meniscus tears. Conservative measures, including treatment of the underlying osteoarthritis, are the mainstay of treatment.
These substantial differences in acute and degenerative meniscus tears are important for the primary care provider to understand because knowing the difference will guide referral patterns. In addition, patients are too often given false hope that there degenerative “tear” can be “fixed” when that is usually not the case.
Managing patient expectations is key to good patient care.