Injury to the meniscus of the knee is common and can occur in any age group. In younger people, the meniscus is fairly tough and rubbery, and a tear usually occurs as a result of a forceful twisting injury. As we age, the meniscus grows weaker, and tears can occur as a result of a fairly minor injury, even from the up and down motion of squatting.
The meniscus, located on either side of the knee joint, acts like a gasket between the femur and the tibia to spread out the weight being transferred from the femur above to the tibia below. Articular cartilage covers the ends of the bones that make up the joint. The articular cartilage surface is a tough, slick material that allows the surfaces to slide against one another without damaging either surface. The ability of the meniscus to spread out the force on the joint surfaces as we walk is important because it protects the articular cartilage from excessive forces occurring in any one area on the joint surface. Without the meniscus, the concentration of force into a small area on the articular cartilage would damage the surface, leading to degeneration over time.
The meniscus also helps with stability of the knee joint, since it converts the tibial surface into a shallow socket. A socket configuration is more stable than a flat surface, as shown below.
Without the meniscus, the round femur would slide freely on top of the flat tibial surface.
The meniscus can be torn in several ways. The entire inner rim of the medial meniscus can be torn in what is called a buckethandle tear.
The meniscus can also have a flap torn from the inner rim,
or the tear can be a degenerative type tear where a portion of the meniscus is frayed and torn in multiple directions.
How does the meniscus cause problems in the knee?
While meniscus injuries can occur in any age group, the causes are somewhat different for each group. Tears in the meniscus in patients under the age of thirty usually occur as a result of a fairly forceful twisting injury, usually involving a sports activity.
In older people, the meniscus grows weaker. The meniscus tissue degenerates and is much easier to tear.
Meniscal tears can occur as we age as a result of a fairly minor injury. Degenerative tears of the meniscus are commonly seen as a part of the overall condition of osteoarthritis of the knee in the senior population. In many cases, no injury to the knee can be contributed to the meniscal tear. Instead, the tear is the result of cumulative wear.
The most common symptom caused by a torn meniscus is pain. The pain may be felt along the joint line where the meniscus is located or may be more vague and involve the whole knee. If the torn portion of the meniscus is large enough, locking may occur.
Locking simply refers to the inability to completely straighten the knee. This occurs when the fragment of torn meniscus gets caught in the hinge mechanism of the knee and will not allow the leg to straighten completely. (Imagine sticking a pencil between the hinges in a door and trying to close it.)
The constant rubbing of the torn meniscus on the articular cartilage may cause wear and tear on the surface, leading to degeneration of the joint.
The knee may swell with use and become stiff and tight. This is usually because of fluid accumulating inside the knee joint, which is sometimes called water on the knee. This is not unique to meniscus tears, but occurs whenever the knee becomes inflamed.
Diagnosis begins with a history and physical. The examination will try to determine where the pain is located, whether or not locking has occurred, and if you have any clicks or pops as the knee is moved. X-rays will not show the torn meniscus; however, they are useful to determine if other conditions are present.
The MRI (Magnetic Resonance Imaging) scan is very effective at showing the meniscus. The MRI machine uses magnetic waves rather than x-rays to show “slices” of the soft tissues of the body. This test does not require any needles or special dye and is painless. If there is uncertainty in the diagnosis following the history and physical examination, or if other injuries in addition to the meniscal tear are suspected, the MRI scan may be suggested.
If the history and physical examination strongly suggest that a torn meniscus is present, then arthroscopy may be suggested to confirm the diagnosis and treat the problem at the same time. Arthroscopy is an operation where a small fiberoptic TV camera is placed into the knee joint. The arthroscope allows your doctor to look into the knee joint and see the condition of the articular cartilage, the ligaments and the menisci.
Initial treatment for a torn meniscus is typically focused on reducing the pain and swelling in the knee. The physician may recommend using crutches for several days to rest the knee and ice to reduce the pain and swelling. If the knee is locked and cannot be straightened, surgery may be recommended as soon as reasonably possible to remove the torn portion. Once a meniscus is torn, it will most likely not heal on its own.
If the symptoms continue, surgery will be required to either remove the torn portion of the meniscus or to repair the tear. Most meniscus surgery is done using the arthroscope. Small incisions are made in the knee to allow the insertion of a small TV camera into the joint. Through another small incision, special instruments are used to remove the torn portion of meniscus, while the arthroscope is used to see what is happening.
In some cases, the meniscus tear can be repaired. In this situation, sutures are placed into the torn meniscus until the tear is repaired.
Repair of the meniscus is not possible in all cases. Young people with relatively recent meniscal tears are the most likely candidates for repair. Degenerative type tears that occur as we age are not usually repairable.