Meniscus Injuries

Within the knee, there are two fibrocartilaginous crescents that sit on top of the tibia (the shin bone). These are the menisci. Their outer rims are thicker than their inner borders. They help to create a sort of seat on top of the tibia for the condyles of the femur. The medial meniscus is C-shaped while the lateral meniscus forms more of an “O”.

The seat formed by the menisci on the joint surface of the tibia helps stabilize the knee joint, especially while weight-bearing, by mediating the incongruence between the top of the tibia and the bottom of the femur. The menisci also serve to:

• Spread loads throughout a higher percentage of the knee joint’s surface area
• Improve lubrication for the joint surfaces within the knee
• Act as shock absorbers
• Facilitate joint proprioception (the body’s awareness of a joint’s movement and location)
• Aid with joint nutrition

A narrow strip along the outer rim of the meniscus is vascular, meaning that it has blood flow and all of the things that come with it, including oxygen, healing cells, and nutrition. The rest of the cartilage of the meniscus is avascular, meaning it does not have a blood supply. The avascular zone instead relies on the joint fluid for nutrition. This is important when a meniscus injury occurs. Tears in the vascular zone are more likely to heal than those in the avascular zone. As a result, meniscal tears are treated with different techniques based on the location of the tear.

Causes

Meniscus tears are caused by a rotation of the knee while the knee is being flexed or extended. Most frequently, the knee is partially flexed at the time of injury. There may also be a valgus (from the outside/lateral side) or varus (from the inside/medial side) force on the knee at the time of injury, too. The rotated and partially flexed position of the knee pinches part of the meniscus between the femur and the tibia, resulting in a tear.

In athletes, meniscus injuries often occur during a cutting motion while running. In performers, this motion is replicated by pushing off for a twisting jump or a leap on a curve. This mechanism of injury can also occur when landing from these jumps.

Repeated mild (Grade 1) knee sprains can reduce the ability of the knee’s ligaments to stabilize the joint. With the reduced ligamentous stability, the task of stabilizing the knee joint falls to other structures, including the menisci. If the ligamentous stability is decreased enough, the menisci can be at a much higher risk of suffering a tear due to the higher forces they must absorb and transmit.

Not all meniscus injuries are acute injuries. Some lateral meniscus tears can be caused by repeated stress on the knee. This type of meniscal injury has an insidious onset, meaning that there does not seem to be one single incident that causes the tear.

Signs and Symptoms

It is important to have your knee evaluated by a medical professional if you experienced a mechanism of injury similar to that which was described above. The symptoms of a meniscal injury can mimic the symptoms of patellofemoral dysfunction, but the treatments can differ substantially. Obtaining an accurate diagnosis early on can improve healing time and effectiveness of treatments.

Symptoms of an acute meniscal tear can include:

• Locking or clicking in the knee
• Pain and tenderness along the joint line (the space between the femur and tibia)
• A sensation of “giving out” in the knee during activity
• Swelling (developing over 2-3 days after the injury)
• Loss of motion of the knee
• Pain with squatting/pliés

Tears in the avascular zone may not cause pain.

The locking, catching, and giving way of the joint is caused when portions of the meniscus get caught between the joint surfaces of the femur and tibia. These portions can be either chunks that tear completely off of the bone and meniscus or a flap of the meniscus that is created by a tear.

Overuse that leads to a meniscal injury can cause recurrent swelling and muscle atrophy. These injuries can also cause a sensation of the knee giving out, a popping sensation, an inability to fully squat, or an inability to change direction quickly without pain. Performers with these symptoms will most likely need surgery.

Treatment and Recovery

If you have symptoms of a meniscal injury, go to a doctor. You may need to get an MRI in order to understand the extent of the injury. Many meniscus injuries occur in conjunction with MCL or ACL tears, so you need to rule out these injuries to ensure that the treatment of your injury is as effective as possible.

Peripheral meniscal tears (in the vascular zone) may heal on their own or can be surgically repaired (and heal well after the surgery) because of the generous blood supply to this area. Meniscal tears that do not heal or cannot be repaired, such as those in the avascular zone, are usually surgically removed.

After a meniscal repair, the knee must be immobilized for 4-6 weeks to allow for proper healing to occur. During this time, the patient is on crutches, progressing from partial to full weight bearing. Despite this period of recovery being called the “immobilization period,” the patient actually can perform active range of motion exercises in a limited range of motion. Once off the crutches, full-range resistive (strengthening) exercises can start, with the rehabilitation program focusing on muscular endurance.

Surgical procedures to remove the injured meniscus are called meniscectomies. As you would expect from their names, partial meniscectomies remove only a portion of the meniscus while full meniscectomies remove the entire meniscus. Since tissue is being removed instead of repaired in a meniscectomy, there is no post-surgical immobilization to allow for healing. After partial meniscectomies, the patient can progress to full weight bearing (on crutches) as soon as they can, and they can return to full activity in as few as 1-2 weeks after surgery, with rehabilitation being progressed based on symptoms. However, removal of the meniscus can lead to a decrease in the joint’s stability and to degenerative changes in the joint surfaces of the knee, so meniscectomies are only performed when conservative care (letting it heal) and meniscal repair are not likely to succeed.

If the injury was caused by repetitive stress, rehabilitation should also focus on correcting any improper mechanics or strength imbalances that may have contributed to the injury.