A Closer Look at the Knee's Vulnerable Crescent. Meniscus injuries rank among the top knee afflictions, with nearly 850,000 surgeries performed annually. Yet, surgery isn't always the answer.
Derived from the Greek for "crescent," the term "meniscus" mirrors the shape of a crescent moon. In North America, these injuries stand out as common knee diagnoses. But, it's worth noting that while some require surgical intervention, many heal through targeted therapy and exercise.
Article Index:
What Causes Meniscal Injuries
Meniscus tears often occur in two ways:
Meniscus injuries are common in sports like football, basketball, soccer, or rugby. These injuries often happen during a twisting motion when the player's knee is bent and their foot is firmly planted on the ground.
In such situations, the meniscus can tear due to the intense pressure created by the rotational movement, as it's squeezed between the tibial and femoral condyles (the rounded ends of the thigh and shin bones).
Frequently, a traumatic meniscal tear takes the form of a vertical or longitudinal split. Sometimes, medial meniscus tears can occur alongside an ACL (anterior cruciate ligament) and an MCL (medial cruciate ligament) tear, which is known as the "Terrible Triad" or "Horrible Triangle." (11)
Meniscus tears can also result from gradual wear and tear during the normal aging process.
As people age, their meniscus becomes less flexible and more prone to tearing. This is typically seen in individuals during their 40s or 50s. Degenerative meniscal tears are more frequently observed in men than in women (12).
Degenerative tearing is one of the leading causes of meniscus injuries. In these instances, the meniscus can tear without the person even realizing it. Due to the degenerative nature of this process, everyday activities like squatting might lead to a tear in the meniscus, particularly in the posterior horn of the medial meniscus.
Increased Risk of Osteoarthritis
Understanding that meniscus injuries can increase the likelihood of developing knee osteoarthritis is crucial. While knee osteoarthritis may not be life-threatening, it can significantly impact a person's quality of life.
Exercise Tip: Avoid reaching maximum flexion during squats is advised for older individuals. Studies have shown a correlation between maximum flexion while performing squats (in older patients) and a higher occurrence of meniscal tears (12).
Anatomy & Biomechanics
The menisci in your knees are crescent-shaped, fibro-cartilaginous structures that contribute to stability, shock absorption, nourishment, and joint lubrication while distributing weight evenly across the knee joint. They transmit 40-60% of the force in the lower extremity; without functional menisci, the knee joints would deteriorate rapidly (5).
Each knee contains two menisci - a lateral meniscus and a medial meniscus. Both have a concave shape on top and a flat bottom, forming a wedge shape. They are thick on the outside and thin on the inside (almost paper-thin), which helps prevent the thigh bone (femur) from slipping off the shinbone (tibia).
The knee bones are coated with an extremely smooth layer of cartilage that enables gliding, reduces friction, and allows for freedom of movement.
The menisci, positioned between these cartilaginous surfaces, offer stability and even weight distribution.
They are situated between the femoral condyles and the tibial plateau.
The medial meniscus is more securely attached than the more mobile lateral meniscus. This firmer attachment may contribute to the higher incidence of medial meniscus injuries than lateral meniscus injuries (15).
Meniscus Motion
Biomechanically, we know that the meniscus in the knee moves in sync with the bones to which it's attached. Above the knee joint, the femur bones (femoral condyles) pull the menisci forward (anterior) during knee extension (straightening the knee) and pull them backward (posterior) during knee flexion (bringing the foot towards your buttocks).
Below the knee joint, as the tibia rotates inward or outward, it pulls the meniscus along with it. When the tibia rotates outward, the lateral meniscus is drawn forward while the medial meniscus moves back. Conversely, if the tibia rotates inward, the medial meniscus moves forward, and the lateral meniscus moves back (10).
Meniscus Injury
The severity of a meniscus injury can vary significantly based on its location. Injuries on the outer edges of the meniscus may take longer to heal due to limited blood flow, but they can still recover.
Key Point: Only 10% to 25% of the meniscus on the periphery is vascularized (2).
The central area of the meniscus lacks blood vessels, meaning it has no circulatory input. Injuries in the center of the meniscus cannot heal themselves, as this area doesn't have a blood supply. Without adequate blood flow, the nutrients needed for healing cannot reach the injured site, and waste by-products aren't removed.
Degree of injury
Meniscus injuries can range from mild to moderate and even severe. Pain and swelling are the most frequent symptoms of a meniscal tear. Such tears are often described as a sharp, stabbing pain rather than a dull ache. In cases of more severe meniscus injuries, an individual may experience "locking of the joint" and significant knee instability.
If "joint locking" occurs, it's crucial to seek immediate medical attention from a sports physician or another medical professional specializing in physical medicine. Your specialist should conduct a physical examination to assess the severity of the injury.
Note: In a severe meniscus injury, loose cartilage (articular cartilage) may break off within the joint. These fragments can cause substantial damage to the knee joint and contribute to degenerative arthritis.
Symptoms are usually worsened by bending and putting weight on the knee. Clicking or a feeling of giving way are common complaints. Activities involving kneeling, squatting, twisting, or pivoting are typically poorly tolerated.
Symptoms
The following offers a general idea of the symptoms associated with varying severity levels of meniscus injuries. Remember that these are only guidelines; consulting a medical professional for a definitive diagnosis is essential.
Symptoms of a minor meniscus tear:
Minimal pain, allowing you to walk.
Some swelling and increased pain when squatting.
Most symptoms should subside within 2-3 weeks of the initial injury.
Symptoms of a moderate meniscus tear:
Pain is located directly at the meniscus site (along the lateral or medial joint line).
Sharp pain during any squatting or twisting motion of the knee.
Significant stiffness.
If these symptoms are ignored and rehabilitation isn't implemented, they may persist for several months to a year.
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, with locking frequently observed in a bucket handle type tear of the meniscus.
The patient often cannot straighten the knee.
Surgical intervention is often necessary in such cases.
Conclusion Part 1
As we delve deep into the intricacies of the meniscus, it becomes evident that this crescent-shaped marvel is more than just a passive structure in the knee. It's a dynamic entity that plays a pivotal role in our mobility, especially in high-impact activities and sports. From the subtleties of its biomechanics to the tell-tale signs of its injuries, the meniscus offers a rich tapestry of insights into knee health.
While surgical interventions stand out as a beacon for some, it's heartening to realize that many can find relief and recovery through less invasive means. As with all medical concerns, early diagnosis and informed decision-making are paramount. The journey through understanding meniscal injuries underscores the importance of knowledge, vigilance, and a proactive approach to our well-being. As we close this chapter on the meniscus, it serves as a reminder of the intricate wonders housed within our bodies and the delicate balance they maintain in our daily lives.
Note: References for Meniscus Injuries - Parts 1 to 3" are in Part 3.
DR. BRIAN ABELSON DC. - The Author
Dr. Abelson's approach in musculoskeletal health care reflects a deep commitment to evidence-based practices and continuous learning. In his work at Kinetic Health in Calgary, Alberta, he focuses on integrating the latest research with a compassionate understanding of each patient's unique needs. As the developer of the Motion Specific Release (MSR) Treatment Systems, he views his role as both a practitioner and an educator, dedicated to sharing knowledge and techniques that can benefit the wider healthcare community. His ongoing efforts in teaching and practice aim to contribute positively to the field of musculoskeletal health, with a constant emphasis on patient-centered care and the collective advancement of treatment methods.
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