Knee pain caused by a meniscus injury is widespread. It may be one of the most common forms of a knee injury. About 850,000 surgical procedures on the meniscus are performed each year (16). The good news is that all meniscus injuries DO NOT require surgery!

If you were wondering, the word meniscus is derived from the Greek word that means "crescent," as in a crescent-shaped moon. Meniscal tears are one of North America's most commonly diagnosed knee injuries. Some meniscus injuries require surgery, and others will heal with a combination of manual therapy and exercise.

WHAT CAUSES MENISCAL TEARS

Meniscus tears often occur in two ways:

1. When playing sports such as football, basketball, soccer, or rugby. The injury often occurs during a torsional motion in which the player’s knee is flexed while the foot is planted on the ground.

In such cases, the meniscus is torn due to the compressive forces that occur with rotation when the meniscus is compressed between the tibial and femoral condyles.

Most of the time, a traumatic meniscal tear is a vertical or longitudinal tear. Medial meniscus tears are also sometimes accompanied by an ACL (anterior cruciate ligament) and an MCL (medial cruciate ligament) tear (also called the “Terrible Triad or Horrible Triangle”). (11)

2. Meniscus tears also occur due to slow degeneration during normal aging.

With age, the meniscus becomes less pliable and is easily torn. This usually happens to individuals in their fourth or fifth decade of life. Degenerative meniscal tears are also more common in men than in women. (12).

Degenerative tearing of the meniscus is one of the most common causes of meniscus injury. In these cases, the meniscus is often torn without the patient knowing it has occurred. With the degenerative process, even everyday activities such as squatting could cause a tear in the meniscus (posterior horn of the medial meniscus).

RISK FACTORS FOR DEVELOPING OSTEOARTHRITIS

It is essential to recognize that meniscus injuries can accelerate the chances of developing knee osteoarthritis. Although knee osteoarthritis is not life-threatening, it can significantly affect the quality of your life.

Exercise Tip: We recommend that older patients avoid reaching maximum flexion when doing squats. Maximum flexion while doing squats (in older patients) has been correlated with an increased incidence of meniscal tears (12).

MENISCUS ANATOMY & BIOMECHANICS

The menisci in your knee are crescent-shaped, fibro-cartilaginous structures that provide stability, shock absorption, nutrition, and joint lubrication while acting to distribute your weight across your knee joint. Forty to sixty percent of the force in the lower extremity is transmitted through the menisci. Without functional menisci, the joints of the knees would soon degenerate. (5)

Each knee has two menisci - a lateral meniscus and a medial meniscus. Both menisci have a concave shape on the top and are flat on the bottom to create a wedge shape. Each meniscus is very thick on the outside and thin on the inside (almost paper thin on the inside). This wedge shape keeps your thigh bone [ femur] from slipping off your shinbone [ tibia].

The bones of your knees are covered with a layer of exceptionally smooth cartilage. This cartilage allows for gliding, reduced friction, and freedom of motion.

The menisci of your knees are located between these cartilaginous surfaces and provide stability and even weight distribution.

The menisci are located between the femoral condyles and the tibial plateau.

The medial meniscus is attached more securely than the lateral meniscus (which is more mobile). This secure level of attachment may be one of the reasons why there is a greater incidence of medial meniscus injury compared to the lateral meniscus. (15)

MENISCUS MOTION

Bio-mechanically, we know that the meniscus of the knee follows the motions of the bones to which they are attached. Above the knee joint, the bones of the femur (femoral condyles) pull the menisci forward [anterior] with knee extension (knee straightening) and pull them backward [posterior] with knee flexion (foot towards your butt).

Below the knee joint, as the tibia rotates internally or externally, it pulls the meniscus with it. As the tibia rotates to the outside - the lateral meniscus is drawn forward while the medial meniscus moves back. If the tibia rotates to the inside, the medial meniscus moves forward, and the lateral meniscus moves back. (10)

MENISCUS INJURY

The severity of a meniscus injury varies greatly depending on its location. Meniscus injuries on the outer edges of the meniscus can be prolonged to heal due to poor circulation, but they can still heal.

Key Point: Only the peripheral 10% to 25% of the meniscus is vascularized. (2)

The center area of the meniscus is avascular. It is without circulatory input. Meniscus injuries that occur within the center of the meniscus do not have the ability to heal themselves since the center of the meniscus does not have a blood supply. Without a good blood supply, nutrients required for healing are not supplied to the area, and waste by-products are not removed.

You could say that the menisci have a design flaw (having such poor circulatory function), but then I would be taking a chance on being struck by lightning. Just joking!

DEGREE OF INJURY

Injuries to the menisci can range from minor to moderate to more severe. Pain and swelling are the most common symptoms of a meniscus tear. Often a meniscal tear is described as a sharp stabbing pain instead of a dull ache. With more severe menisci injuries, a person may notice some “locking of the joint” accompanied by considerable knee instability.

If “locking of the joint” occurs, it is imperative to immediately obtain medical attention from a sports physician or other medical practitioner who works with physical medicine. Your specialist should perform a physical examination on you to determine the severity of the injury.

Note: In a severe meniscus injury, loose cartilage (articular cartilage) may break off within the joint. These pieces can cause considerable damage to the knee joint and lead to degenerative arthritis.

Symptoms are commonly aggravated by flexing and loading the knee. Complaints of clicking or a feeling of giving away are common. Any activity that requires kneeling, squatting, twisting or pivoting is poorly tolerated.

SYMPTOMS OF MENISCUS INJURY

The following gives you a basic idea of the symptoms associated with the severity levels of menisci injury. Please be aware that these are general guidelines, to make a definitive diagnosis a medical professional should be consulted.

Symptoms of a minor meniscus tear:

• Only minimal pain - you are still able to walk.

• Some degree of swelling with increased pain when squatting.

• Most of these symptoms should diminish within 2-3 weeks of initial injury.

Symptoms of a moderate meniscus tear:

• Pain directly at the site of the meniscus (along the lateral or medial joint line).

• Sharp pain with any type of squatting or twisting motion of the knee.

• Considerable stiffness.

• If these symptoms are ignored and rehabilitation is not implemented it could take several months to a year before they go away.

Symptoms of a severe meniscus tear:

• Immediate sharp pain, swelling, and stiffness in the knee.

• The knee may lock into position. A locked knee can often be pathognomonic for a meniscus Injury. locking is often seen with a bucket handle type tear of the meniscus.

• The patient is often unable to straighten the knee.

• This is often a case for surgical intervention.

CONCLUSION PART 1

Meniscus injuries usually occur in one of two ways.

1. The first is where the meniscus is torn due to the compressive forces that occur with rotation when the meniscus is entrapped between two bones (tibial and femoral condyles).

2. In the second case, meniscus tears often occur due to the slow degeneration that occurs with normal aging. With age, the meniscus becomes less pliable and is easily torn.

The severity of a meniscus injury varies greatly depending on its location.

• Meniscus injuries on the outer edges of the meniscus can be very slow to heal due to poor circulation but they can still heal.

• Meniscus injuries that occur within the center of the meniscus do not have the ability to heal themselves since the center of the meniscus does not have a blood supply.

Injuries to the menisci can range from minor to moderate to more severe. Meniscus injury symptoms can often give us some indication of the severity of the damage.

Meniscus Injuries Part 1 - What Are You Dealing With

Meniscus Injuries Part 2 - Diagnosis & Acute Stage

Meniscus Injuries Part 3 - Treatment Approaches

Note: References for Meniscus Injuries - Part 1 to 3" in Part 3.

DR. BRIAN ABELSON DC.

Dr. Abelson believes in running an Evidence-Based Practice (EBP). EBPs strive to adhere to the best research evidence available while combining their clinical expertise with the specific values of each patient.

Dr. Abelson is the Motion Specific Release (MSR) Treatment Systems developer. His clinical practice is located in Calgary, Alberta (Kinetic Health). He has recently authored his 10th publication, which will be available later this year.

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