What Causes a Meniscus Injury?

The medial meniscus is more often injured than the lateral meniscus. Medial meniscus tears generally occur in the posterior (back) horn, which is prone to injury and harder to manage than tears in the body (center), the anterior (front), or on the periphery (outside). The posterior horn is more contained and carries more of the load than the other areas and it is difficult to reach because there are bones in the way. Peripheral tears occur on the outside near the attachment to the knee capsule. They receive a lot of blood supply, so they are easily repaired. These tears often occur in conjunction with an ACL or MCL injury.

Who is at risk?

Although knee injuries are more common in women than men, men experience more meniscus injuries and tears (approximately 2.5 males: 1 female). This is believed to be due to men's participation in more aggressive sports and manual activities. For men, meniscal injuries occur most often between the ages of 31 to 40; for females mensical tears usually occur between 11 and 20 years. Occupations such as mining or carpet-laying (where you spend a lot of time in the squat position), or participation in contact sports or repetitive stress activities (such as running and skiing) are prone to meniscus injuries.

The 2 most common causes of meniscus injuries are acute trauma to the knee and degeneration of the knee joint tissue. In either case, a piece of the meniscus can loosen or tear and move around in your joint interfering with your normal knee movement and function. A person with a discoid meniscus (menisci) is also at greater risk of experiencing a meniscus tear or damage.

Acute Trauma

Forceful blows to the knee occur most frequently during activities such as rugby, football, baseball, soccer, basketball or racquet sports when you twist your knee, or slow down too quickly. A meniscus injury can result during a hit by forceful rotation of the knee while the foot is firmly planted and bearing weight. A meniscus tear can also occur from hyper flexion or hyperextension of your knee (flexion or extension beyond your knee¹s normal range of motion). Hyper flexion or hyperextension can occur during a car accident, while participating in sports or exercising, or during other low-impact activities if the knee is unstable.

These types of tears generally affect athletes or those under 40 years of age. A medial meniscus tear will frequently occur along with other injuries such as an MCL and/or ACL tear. The combined injuries are seen most often in contact sports, when an athlete gets hit on the outside of a bent knee. A lateral meniscus tear will result more often from a knee that is bent (flexed) excessively and experiences full weight bearing, while the thighbone is turning outward; seen in sports such as skiing.

Degeneration of the Fibrocartilage

In younger people, the meniscus is very flexible and pliable (like a new rubber tire). Over time, the meniscui tissue weakens and becomes less flexible, more brittle and develops small cracks in it (like those seen in an aged car tire). In addition, normal wear and tear on the knee tissue can also lead to osteoarthritis. If osteoarthritis sets in, destructive chemical substances are released in the joint cavity which further breakdown the collagen fibers. As the menisci degenerate they become more susceptible to tears which can lead to a meniscus tearing without any associated injury.

Approximately 60% of people over 65 years of age will experience some form of degenerative meniscus tear. Unfortunately, the blood supply to the menisci decreases by 20% by the age of 40 and the body's ability to heal itself becomes inhibited. As a result, it is more difficult to heal a tear caused by deterioration than an acute trauma that occurs earlier in life. With the use of Blood Flow Stimulation Therapy (BFST) and Ultrasound Therapy, blood flow can be increased to promote faster and more complete healing of a meniscus tear.

Discoid Meniscus

When in the womb your menisci are flat and disc shaped rather than crescent shaped wedges. When the meniscus does not develop into a crescent shape it is referred to as a discoid meniscus. A discoid meniscus generally occurs in the lateral meniscus (1.5-3% of the general population) but can appear in the medial meniscus (0.1-0.3%). The Asian population has a greater frequency of discoid menisci the rest of the world (approximately 17% lateral discoid menisci reported). A discoid meniscus is generally found in children less than 11 years of ago but the meniscus will often change to a c-shape with maturity so children will grow out of their symptoms.

The symptoms associated with a discoid meniscus can vary greatly depending on the type, location and presence of a tear. A stable discoid meniscus may be asymptomatic; only becoming symptomatic if a tear occurs. If there is a tear present, clicking, snapping, buckling and/or locking of the knee joint, decreased range of motion, joint pain and tenderness, and atrophied quadriceps (muscles wasting away) may be experienced. A discoid meniscus has also been referred to as "snapping knee syndrome".