A Closer Look at the Knee's Resilient Crescent. Meniscus injuries are a common challenge, with nearly 850,000 surgeries performed annually. However, surgery isn't always the best solution.
The term "meniscus," derived from the Greek word for "crescent," reflects its crescent moon shape. Meniscus injuries are a frequent diagnosis in North America, but there's good news! Many of these injuries can heal effectively through targeted therapy and exercise, offering a less invasive path to recovery.
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. They 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).
A traumatic meniscal tear frequently 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 normal aging.
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 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, which 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 of Meniscus Injuries
The menisci in your knees are crescent-shaped fibrocartilaginous structures essential for stability, shock absorption, nourishment, and joint lubrication. They evenly distribute weight across the knee joint and transmit 40-60% of the force in the lower extremity, preventing rapid deterioration of knee joints.
Each knee has a lateral and medial meniscus with a concave top and flat bottom, forming a wedge shape. They are thick on the outside and thin on the inside, preventing the thigh bone (femur) from slipping off the shinbone (tibia). These menisci are positioned between the femoral condyles and the tibial plateau, providing stability and even weight distribution.
The medial meniscus is more securely attached than the more mobile lateral meniscus, contributing to the higher incidence of medial meniscus injuries. The knee bones are coated with smooth cartilage, enabling gliding, reducing friction, and allowing for freedom of movement.
Meniscus Motion
Biomechanically, the meniscus in the knee moves in sync with the bones to which it is attached. During knee extension (straightening), the femoral condyles pull the menisci forward, and during knee flexion (bending), they pull the menisci backward.
Below the knee joint, the tibia's rotation also influences the menisci. When the tibia rotates outward, the lateral meniscus moves forward, while the medial meniscus moves backward. Conversely, when the tibia rotates inward, the medial meniscus moves forward, and the lateral meniscus moves backward.
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 more severe meniscus injuries, an individual may experience "locking of the joint" and significant knee instability.
If "joint locking" occurs, it is 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.
Bending and putting weight on the knee usually worsen symptoms. 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 - Meniscus Injuries Part 1
Meniscus injuries, often called the knee's resilient crescent, are a common challenge among athletes and the general population. With nearly 850,000 surgeries performed annually, it’s clear that meniscus injuries are prevalent. However, it's encouraging to note that surgery is not always the only option. Many meniscus injuries can heal effectively through targeted therapy and exercise, providing a less invasive and often highly effective path to recovery.
Understanding the anatomy and biomechanics of the meniscus is crucial in managing these injuries. The menisci are crescent-shaped structures that play vital roles in knee stability, shock absorption, and weight distribution. Injuries can occur due to sports-related activities or gradual wear and tear with aging. While some severe cases may require surgical intervention, many can be addressed with conservative management involving physical therapy and specific exercises.
Note: References for Meniscus Injuries - Parts 1 to 3" are in Part 3.
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