What is meniscus degeneration?
Each knee has two menisci. The medial meniscus sits between the tibia and the femur in the part of the knee closest to the midline (middle) of the body. The lateral meniscus sits between the tibia and femur in the part of the knee furthest away from the midline. The meniscus serves the important function of transmitting forces across the knee evenly when performing the weight-bearing activity. Due to their crescent shape and the fact that they are triangular in cross-section, they allow the rounded part of the bottom of the femur to fit better on the flat part of the top of the tibia. In addition, the meniscus helps to maintain the stability of the knee, improves lubrication of the knee, and absorbs some of the forces when performing weight-bearing activity.
There are two broad types of tears: Traumatic and Degenerative. Traumatic tears occur when there is a twisting or hyperflexion (deep bend) injury to the knee. These occur when playing sports such as football, skiing, squash or netball. Degenerative tears are more common in people over 40 and sometimes can occur without an obvious injury. Degenerative tears occur when the “ageing meniscus”, which is stiffer than those of younger people, gets pinched between the femur and tibia. This can occur with innocuous movements such as getting out of a low car or stepping off a kerb.
Degenerative tears can be thought of as a “fraying” of the meniscus rather than a clean tear through the tissue. Smokers are at a higher risk of degenerative tears. Sometimes the symptoms from a torn meniscus can be confused with those caused by significant knee arthritis.
What are the symptoms of meniscus degeneration?
In degenerative meniscal tears, the pain in the knee can come on gradually without an obvious injury. The pain in the knee can be activity-related and there is less likely to be any true catching, locking or giving way. The knee may be mildly swollen although excessive swelling is unusual.
How is it diagnosed?
Knee osteoarthritis is diagnosed on the basis of X rays. Rarely, if there is some confusion regarding the diagnosis, an MRI may be needed, however, this is unusual.
What are my options for treatment?
Because the meniscus has a poor blood supply that comes from the periphery of the meniscus, it has poor healing potential. This means that it is unlikely to heal on its own. In addition, because the knee movement will move the injured meniscus, the environment of the knee is not conducive to healing.
The British Association for Surgery of the Knee (BASK) has very clear guidelines on who should and should not have an operation on their meniscus. When the meniscal tear is merely causing pain, then a period of physiotherapy plus injections is recommended for the first three months, followed by reassessment. An operation may be suitable at that point.
In patients where the tear is secondary to arthritis in the knee, then an operation is not recommended as research shows it will not help with symptoms. In this situation, physiotherapy and injections are the main treatment options, with further attention to the arthritic knee at a later date.
Degenerative or complex tears are not suitable for repair.