Although knee injuries are more common in women than men, men experience more meniscus injuries and tears (the ratio is approximately 2.5 males: 1 female). This is believed to be due to men's participation in more aggressive sports and manual activities. The peak incidence of meniscal injuries for males is between 31 - 40 years, whereas for females peak incidence is between 11 - 20 years.

The 2 most common causes of meniscus injuries are acute trauma to the knee and degeneration of the knee joint. 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.

Acute or traumatic meniscus damage can result from forceful rotating of a straight or bent knee while your foot is firmly planted and bearing weight, or from hyper flexion or hyperextension of your knee (flexion or extension beyond your knee¹s normal range of motion). These injuries are experienced most frequently in activities such as rugby, football, baseball, soccer, basketball or racquet sports when you twist or pivot on your knee, or slow down too quickly. The result will generally be a partial or complete medial meniscus tear. This type of tear generally affects athletes or those under 40 years of age. A medial meniscus tear will frequently occur along with other injuries such as an MCL 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. It can also be injured in collisions that involve deep knee bends.

Degeneration of the knee joint involves weakening of your tissues with age, which results from small repetitive movements such as squatting or pivoting positions, or a minor meniscus injury that never healed properly. When you are young your meniscus is very flexible and pliable (like a new rubber tire), as you get older it becomes less flexible and more brittle, it also develops cracks in it (like those seen in an aged car tire). Your articular cartilage and meniscus deteriorate as you age, which can eventually lead to a degenerative tear without any major trauma. You will also experience a 20% decrease in blood supply to your menisci by age 40 due to weight bearing over time; this inhibits your body's ability to heal itself. This wear and tear over the years can lead to an osteoarthritis condition. Destructive chemical substances are then released in the joint cavity, which further breakdown these collagen fibers. Approximately 60% of people over 65 years of age will experience some form of degenerative meniscus tear.

A piece of the meniscus can loosen or tear due to the above causes and move about in your joint. When the tear interferes with normal knee mechanics, the torn fragment of meniscus can catch, lock, or slip between the femur and tibia as your knee moves. As it tries to work its way out, you will normally experience pain, weakness and/or immobility.

A Discoid meniscus occurs when you are born with a more flat, disc shaped meniscus rather than a crescent shaped, wedge meniscus. It is generally found in the lateral meniscus and in kids less than 11 years of age. The symptoms associated with a discoid meniscus can range from very mild to continuous clicking, snapping, buckling and/or locking of the knee joint, decreased range of motion, joint pain and tenderness, and atrophied quadriceps (muscles wasting away). The meniscus will often change to a c-shape with maturity and kids/teens will grow out of their symptoms; however failure of normal development can be experienced.