The purpose of this article is to discuss the mechanism of meniscus tears (which usually occur in females over the age of forty). We will discuss the prevention of meniscus injuries and the treatment of meniscus injuries.
Let’s review meniscus anatomy before we discuss injury. The meniscus of the knee consists of two rings of cartilage that seal the gap between the rounded ends of the femur and the flat ends of the tibia. The seal is fairly tight, similar to the way that a washer forms a seal between a bolt and a nut. The menisci are wedge-shaped along their outer edge. The lateral meniscal ring is circle-shaped, and the medial ring is crescent-shaped. They each consist of three layers of collagen fibers that allow them to be tough and flexible. The outermost fibrous layer runs along the outer curve, tying together all the layers, and resisting shear force at the knee. The middle layer fibers are attached around the edge to resist the stress of weight bearing. The deepest layer runs parallel to the outer edge of the meniscus.
The outer borders of the meniscus are attached to the tibia by coronary ligaments, while the medial borders are free to move within the joint. The medial meniscus also attaches to the medial collateral ligament (MCL). The blood flow properties of the menisci influence the healing process after injury and the potential for an athlete’s return to play.
The only part of the meniscus that receives a direct blood supply is the outer layers (the red zone), which makeup about 10-30% of each meniscus. The remaining layers (the white zone) are nourished only by the synovial fluid, which diffuses from the joint.
Menisci are designed to transfer load across the knee joint by increasing the contact surface area. Joint contact pressure increases by 50-200% when a meniscus has been removed from the knee1. The other functions of the meniscus include absorbing shock, lubricating the joint, and facilitating bone-on-bone gliding as the knee flexes and extends. They are displaced towards the rear of the joint when the knee extends, and towards the front of the joint when the knee flexes. The lateral meniscus moves a bit more than the medial meniscus, due to the connections between the medial meniscus and the MCL, and its firmer attachment of the medial meniscus to the tibia.
Why Meniscus Injuries Occur
There are two types of meniscus injuries, traumatic and degenerative. Degenerative injuries happen slowly over time, and do not require an acute trauma for a tear to develop. Traumatic injuries usually occur in athletes. The most common injury mechanisms are hyper flexion of the knee, lateral trauma, and hyperextension of the knee. When the knee is rapidly hyperextended, the femur can press into a piece of the meniscus that hasn’t had time to glide back out of the way. The resulting stress can result in a tear along the outer part of the meniscus (longitudinal or “bucket-handle” tear).
When the knee sustains impact from the lateral side, the leg is forced into a “valgus” position with rotation. This can happen either from a collision to the outside of the knee, or from a “plant and cut” maneuver. In this position, the MCL is under stress, and the medial meniscus may pull away from its attachment to this ligament. The MCL may also sustain a tear in this position. If the anterior cruciate ligament (ACL) is torn as well, it is known as the “terrible triad” of knee injuries.
If the knee gets flexed beyond its normal range, the back of the lateral meniscus may get torn. There are several types of tears that may occur due to this injury mechanism, a radial tear being the most serious, as it disrupts the outer fibers and affects the ability of the meniscus to bear circumferential stress.
A traumatic meniscus injury may result in a sudden feeling of “giving way,” and the athlete may feel or hear a “pop.” Pain and swelling may come on rapidly, even though they may feel like they are able to continue play. The knee may “lock up” with a small ROM if a torn piece of the meniscus “floats” into the joint space. 73% of tears occur in soccer, basketball, and skiing2.
Treatment of meniscus injuries
At-home treatment for a meniscus injury includes rest, ice, compression, and elevation of the knee. Clinical tests can predict whether a meniscus tear has occurred, and an MRI will confirm a tear. If there is a small tear in the red zone, it is recommended that the athlete rest from sports, immobilize the knee, and consider using crutches for a few weeks until the meniscus can heal. If a larger tear is present, arthroscopic surgery is generally recommended. Most athletes can return to sport at or near their previous level of competition following the surgery. In one study, the mean time between injury and return to play was 5.6 months3.
When surgical repairs do fail, it is usually due to performing the same activity that caused the initial injury. The most important factor in determining success of the surgery was the location of the tear. Tears further from the red zone/white zone junction are more likely to fail, as are complex tears.
When the tear is in the white zone, a surgical removal (partial or complete) may be needed. There are benefits and risks to meniscus removal surgery. On the positive side, aggressive rehab can begin quickly and the athlete can get back to training as quickly as two weeks after surgery. The risk is that osteoarthritis may develop. According to a study in the American Journal of Sports Medicine, patients who underwent the meniscus removal surgery were ten times more likely than patients who didn’t have a knee injury to develop osteoarthritis twenty years after the surgery4. Repairing the tear didn’t necessarily guarantee that osteoarthritis wouldn’t occur.
Some risk factors that would make it more difficult for an athlete to return to play after meniscus removal surgery include being female, over forty years of age, BMI>30, more than one-third of the meniscus removed, and abnormal alignment of the hip, knee, and foot.
Another thing to think about is how we can best take pressure off the meniscus. A knee that is out-of-alignment, or has imbalanced or tight muscles pulling on it is more prone to developing meniscus issues. The IT band has an attachment into the lateral meniscus. Often the IT band needs to be foam-rolled, or treated with a soft tissue technique such as Active Release Techniques (ART). Additionally, the foot and hip need to be addressed, as tightness or fixations in either area can impact the integrity of the knee. Anytime muscles and tissues are overworked or shortened, the body lays down scar tissue to protect the area. Scar tissue is your body’s self-defense mechanism to try to hold a damaged area together, but it also negatively affects the functioning of your tissues. ART is an efficient technique to break up this scar tissue, to allow your muscles and connective tissues to return to normal function. There are also ART protocols for the meniscus area itself. It can sometimes get caught at the front or the back of the knee joint, and it is possible to manually release the meniscus through this technique.
Prevention of meniscus injuries
If we can reduce the pressure on the meniscus in the first place, the likelihood of injury will be lower. The hip, knee, and ankle need to be in proper alignment during running and throughout the gait cycle. If the knee is varus or valgus, it can put pressure on the meniscus
It has been demonstrated that core proprioception, that is, the body’s sense of where it is in space, can predict knee injury in women5. A decrease in proprioception and control in the core can decrease stability and control at the knee. Following are some exercises that can increase core strength and balance.
Stand on a wobble board or a balance mat. Pass a ball to your partner while you both stand on two legs. Then stand on one leg each and pass the ball. If you want to make it harder, throw with your non-dominant hand. Try dribbling the ball with one hand, and then close your eyes and see how long you can continue dribbling. Do a set of double-leg squats, and then a set of single-leg squats. Try to pull or push your partner off balance (keep it clean if you’re the competitive type).
Double-leg: Feet hip width apart, toes pointing forward or slightly outward. Arms overhead or out in front for balance. Push your butt back as if you were going to sit in a chair. Squat down until your upper and lower leg forms a 90-degree angle. Push back up to standing.
Single-leg: Same stance as above. Hold a chair for balance if needed, squat down on one leg, holding the other leg in front of you or behind you.
Single-leg decline: Stand on a decline block or a surface that is slanted downward at about 45 degrees. On one leg, lower down in a squat position until your upper and lower leg form a 90-degree angle. Push up to standing with both legs. All the work here is done in the lowering phase.
Isometric VMO hold: Stand with feet hip width apart, toes pointed outwards. Without lifting your feet off the ground, isometrically contract your leg muscles as if you were going to rotate your feet so they were pointing straight ahead. Don’t actually move your feet!
Nordic hamstring exercise: From a kneeling position with a partner holding your feet, tighten your core, and then let your body fall towards the floor, catching yourself with your hands just before you hit the floor. Push up to kneeling position and repeat.
For Explosive Power:
Plyometrics are exercises done to increase your power, that is, your strength at quick movements. Examples of plyometrics include box jumps, forward and back jumps, tuck jumps, and hurdle jumps.
Any running drills that approximate the movements of sport are good for injury prevention. Examples include running with high knees, kicking feet to butt, side-stepping, side-running with legs crossing alternately in front and behind, and skips.
Please feel free to contact us if you have any questions about meniscus tears or other knee injuries.
1. Am J Sports Med. 2009; 37:124-129.
2. Am J Sports Med. 2006;34:1170-1175.
3. Am J Sports Med. 2009;37:1131-1134.
4. Am J Sports Med. 2007; 35:1756-1769.
5. Am J Sports Med. 2007;35(3):368-373.