The meniscus is a C-shaped disc like cushion of cartilage located between the two bones of the leg (femur and tibia). There are two menisci in each knee, the medial meniscus (inside of the knee) and lateral meniscus (outside of the knee). Although both the femur and tibia are coated with a slippery glide cartilage called "articular cartilage", the meniscus is a cushion called "fibro cartilage", which helps to spread out and dampen the forces across the articular cartilage surfaces. The meniscus has several functions:

• Stability- the meniscus help cup the joint surfaces and they assist the ligaments in providing additional stability in the knee.
• Lubrication and nutrition- the menisci act as spacers between the two bones preventing friction and allowing for the diffusion of the normal joint fluid and its nutrients to the tissue which covers the end of the bone (articular cartilage). Maintaining the integrity of the articular cartilage is critical to preventing the development of arthritis.
• Shock absorption- The C shaped pieces of meniscal fibro cartilage tissue can bear up to 80% of the load across the knee thereby lowering the stresses applied to the articular cartilage. This helps to prevent the development of degenerative arthritis.

There are two different mechanisms for tearing a meniscus. Traumatic tears occur when a sudden load being applied to the meniscal tissue is severe enough to cause the cartilage to fail and let go or split. These usually occur from a twisting fall, injury or a blow to the side of the knee. In a person under 30 years of age this typically requires a fairly violent event although any age group can sustain a traumatic tear. Degenerative meniscal tears are failure of the meniscus over time. There is a natural drying out of the inner center of the meniscus that can begin in the late 20's and progresses with age. Young meniscal cartilage is very flexible, like rubber. As it gets older it becomes like an old tire and becomes hard, less flexible, more brittle and can develop cracks in it. These degenerative tears can occur with or without sudden injury. Meniscal injury or degeneration can also be a result of overuse. Repetitive squatting or kneeling can cause meniscal wear and make it more likely to tear.

Symptoms

• Pain
• Knee catches or locks
• Knee gives out
• Swelling
• Inability to squat, Hop or Run

The most common problem 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 portion of the tear is large enough, locking or catching may occur. Sometimes the knee becomes locked in a bent position and is quite painful. This is often caused by the mechanical blockage of the joint from a displaced meniscal tear which becomes lodged between the ends of the femur and tibia. The torn fragment acts like a wedge to prevent the joint from moving. Clicking or popping, and swelling (water on the knee) are also common complaints. Typically when the meniscus is damaged, the torn piece flips back and forth inside the knee as you walk. Giving way or buckling episodes will be noted if this occurs. Twisting, squatting or impact activities can pinch the meniscus and increase the tear. Often the pain may improve with rest after the initial injury but as soon as aggressive activity is attempted the pain returns. Because the space between the bones of the joint is very small, the torn flap is easily caught between the bones of the joint (femur and tibia). When this happens, the knee becomes painful, swollen, collapses or may be difficult to move again.

The meniscus has almost no blood supply. The exception to this is the peripheral edge of the meniscus which provides the outermost 20% of the meniscus with a blood supply. As a result of this poor blood supply a torn meniscus doesn't have the ability to heal itself very well unless there is just a small tear confined to the peripheral vascular zone. Poor healing also occurs because the meniscus is a small tissue which is subject to significant and constant stress every time a person stands, walks, or runs.

Risk Factors

• Obesity
• Occupations that stress joints (carpenter, plumber)
• Pivoting sports like basketball, skiing, soccer
• Weight bearing collision sports especially football and rugby
• Aging
• Previous knee injury
• Poor muscle conditioning
• Poor nutrition

Diagnosis and Initial Treatment
When evaluating an injured knee, a history is taken to determine the specific symptoms and mechanisms of injury. A physical examination of the knee will be performed to determine the site of pain and any physical findings that are known to be associated with a torn meniscus. X-rays will not show the torn meniscus, but they are useful to determine if other conditions are present that may give similar problems to those of a torn meniscus. In some instances, additional diagnostic tests such as an MRI may be ordered. The MRI can be quite helpful to aid in the diagnosis if clinical signs and symptoms are not clearly defined. It should be noted that the MRI is approximately 85% accurate.

Physical therapy is directed towards reducing the pain and swelling in the knee and regaining the normal range of motion in the knee (full bending and straightening). Modalities such as electrical stimulation and ultrasound may be used to help increase the blood flow to the area and aid in the healing process. Strengthening exercises for the muscles of the entire leg should also be started.

Surgery
If no relief with rehabilitative physical therapy occurs, arthroscopic surgery may be indicated. Arthroscopy involves removing the smallest possible amount of torn tissue in order to preserve as much cushion for the joint as possible. It was once thought that the entire meniscus should be removed if damaged and it would grow back. This was incorrect and now many people who had their entire meniscus removed are suffering from painful degenerative arthritis with the possibility of needing knee joint replacement surgery.

Repair of the meniscus in most cases is not possible. However young people with relatively recent meniscal tears are more likely candidates for repair. In a repair sutures or absorbable tacks are placed into the torn meniscus. Due to the slow healing process of the meniscus the recovery time is longer then when simply removing the torn piece of meniscus. Unfortunately with age and meniscal degenerative changes; the possibility of the tear being repairable greatly decreases. Complete degenerative type tears in older people are not repairable.

In rare cases where a large portion of the meniscus has to be removed, but arthritis is minimal, a technique of transplantation of a meniscus from a cadaver is in the investigational stages.

Post Op
Arthroscopic partial meniscectomy is usually done on an outpatient basis. On average most patients are able to walk without crutches within 48 hours. An active physical therapy rehabilitation program is initiated 1-3 days after surgery. Patients are usually restricted from sports play for approximately 4-6 weeks after surgery, but this is dependent upon the magnitude of knee damage including the presence of arthritis and also the level of pre-surgery muscle conditioning. If successful rehabilitation (e.g. full strength, endurance, and flexibility with no signs of inflammation) is completed an earlier return to sports can be contemplated.