Introduction (What is the meniscus?)
The meniscus consists of connective tissue containing high amounts of collagen fibers with chondrocytes in-between.
The knee joint contains two cartilaginous cushions between the femur and tibia, namely the medial meniscus and lateral meniscus.
Main functions of menisci:
- They help stabilize knee joints.
- They help reduce friction in the knee between the femur and tibia, and absorb shocks during walking and running.
- They help disperse the synovial fluid on cartilaginous surfaces inside the joint.
- They help disperse the weight of the body on the whole surface of tibia to maintain the articular cartilages covering bone surfaces.
The medial meniscus is crescent-shaped, connected to the medial collateral ligament, and it is exposed to highest pressure during lateral rotation of the knee.
The lateral meniscus is more circular than crescent-shaped, not connected to the lateral collateral ligament, so it has a wider range of movement than the medial meniscus, having double the range of movement during knee flexion; therefore it is less predisposed to injury than medial meniscus. Both menisci are connected together by a transverse ligament at the anterior aspect.
The menisci function to disperse pressure on the articular surfaces. They absorb 30-70% of pressure on the articular surfaces with more load on the posterior horn of the meniscus, the degree of pressure on menisci depends on degree of flexion of the knee, as they absorb 50% of pressure during knee extension, and 80% of pressure during knee flexion.
Scientific studies have shown that complete removal of the medial meniscus will lead to reduction of the articular surface area by 50-70%, which means much more pressure on articular cartilages.
Causes of torn meniscus:
The causes of torn meniscus vary according to age group
- In early age, the tear may be associated with discoid meniscus.
- In young adults and athletes, torn meniscus may occur because of knee joint injury in cases of falling or twisting of the knee. Torn meniscus can co-occur with other knee injuries like anterior cruciate ligament tear.
- In old age, torn meniscus may occur without severe knee injury, as a result of weakness and degeneration of the menisci with age, especially in cases of knee osteoarthritis.
There are two other causes: External injuries and degenerative changes:
May result from twisting of the knee joint during falling or sport injuries, In this case torn meniscus may occur solely or associated with other injuries like anterior cruciate ligament tear.
Degenerative changes of menisci:
Usually occur with aging or sometimes with chronic exhaustion of menisci, as in cases of articular cartilage injury.
The potential of torn meniscus increases with bowed legs; due to increased load on the medial meniscus in cases of genu valgus, and increased load on lateral meniscus in cases of genu varum.
Symptoms of medial meniscus injury:
- Pain on the medial aspect of the knee during or after activities.
- Sudden joint locking in various positions, so the patient can't extend or flex his knee, it is fixed in a certain position.
- Pain in the medial aspect of the knee during full extension or flexion, and also during lateral rotation of the knee in flexed position of 70-90 degrees.
- Mild swelling of the knee due to accumulation of joint fluid, usually after activities, especially exhausting ones.
Symptoms of lateral meniscus injury:
- Pain on the lateral aspect of the knee during and after activities. Pain often reoccurs after certain activities.
- Sudden joint locking.
- Pain during full extension or flexion, and also during medial rotation of the knee in flexed position of 70-90 degrees.
- Mild swelling of the knee and joint effusion sometimes.
Management decision in cases of torn meniscus depends upon many factors, which include:
- Factors related to the patient, like age and type of practiced activities.
- Factors related to the type of tear and its symptoms.
- Severity of symptoms and duration of injury, they are important factors affecting the decision of early surgery.
Non-surgical treatment (conservative treatment):
At the time of injury:
- Put ice on the patient's knee while elevating it upward.
- Put a pressure bandage to reduce possibility of knee effusion.
- The patient is given medications to reduce pain and swelling.
- The patient should avoid extreme sports for a duration set by his treating physician.
- Cases of torn meniscus associated with knee osteoarthritis can be managed without surgery, as long as there is no dynamic problem like sudden knee locking. Some studies have shown that about 60% of elderly patients without knee pain have torn meniscus in MRI scan.
- If the patient has knee locking, the tear is repaired by endoscopy.
- Platelet-rich plasma can help in meniscus repair, and recently there are knee injections.
- If symptoms are diminished by non-surgical treatment, there is no indication for other interventions.