Meniscus of the Knee
- Meniscus of the Knee is a crescent shape structure, triangular in cross section, that cover one half to two thirds of the articular surface of the corresponding tibial plateau.
- There are two Meniscus in the knee, Medial Meniscus and Lateral Meniscus.
- 50% of medial tibial plateau covered by medial meniscus, whereas 59% of lateral tibial plateau covered by lateral meniscus.
The meniscus functions are:
- The meniscus of the knee acts as a joint filler.
- Compensate for gross incongruity between femoral and tibial articulating surfaces.
- Prevent capsular and synovial impingement during flexion-extension movements.
- joint lubrication function, helping to distribute synovial fluid throughout the joint and aiding the nutrition of the articular cartilage.
- Contribute to stability in all planes but are especially important rotary stabilizers.
- Reduce the stress on the articular cartilage; they prevent mechanical damage to both the chondrocytes and the extracellular matrix
- Shock or energy absorbing functions (from 40% to 60% of the superimposed weight in the standing position are carried by the menisci).
See Also: Knee Meniscus Tear
Composition of Meniscus of the Knee:
- The Meniscus composed of dense, tightly woven collagen fibers:
- 90 % Type I collagen.
- 65-75% water
- Cellular elements.
- The collagen fibers arranged in many direction:
- Longitudinal (circumferential)
- perforating fibers ( a little)
- This arrangement provides great elasticity and ability to withstand compression.
Meniscus Blood Supply:
The main blood supply to the meniscus of the knee comes from:
- The lateral geniculate artery: Supply 10-25 % from peripheral region of the lateral meniscus.
- Medial geniculate artery: Supply 20-30 % from peripheral region of the medial meniscus.
- The lateral and medial geniculate artery is a branch of the popliteal artery.
There are three vascular zones of the Meniscus:
- Red-Red zone:
- Completely within the vascular zone.
- Tears within this zone have the highest healing potential.
- Red-White zone:
- Intermediate vascularity.
- Less predictable healing.
- Red-Red and Red-White comprise the outer 4 mm of the meniscus.
- White-White zone:
- Nutrition solely derived from synovial fluid via passive diffusion.
- Poor healing response
- Other parts receive nutrition through diffusion from the synovial fluid.
- The medial meniscus of the knee is a C-shaped structure larger in radius than the lateral meniscus.
- Posterior horn is wider than the anterior horn.
- Most of the weight is borne on the posterior portion of the meniscus.
- The peripheral attachments are more rigid than the lateral meniscus.
- The average width is 9 to 10 mm , and the average thickness is 3 to 5 mm.
- It is likely to be injured during rotation because:
- Its anterior and posterior attachments follow the tibia, but its intervening part follows the femur.
- Medial meniscus tears occur more often with chronic anterior cruciate ligament deficiency.
- The lateral meniscus of the knee is more circular in form, covering up to two thirds of the articular surface of the underlying tibial plateau.
- The tendon of the popliteus muscle separates the posterolateral periphery of the lateral meniscus from the joint capsule and the fibular collateral ligament.
- It’s more mobile than the medial meniscus.
- The average width is 10 to 12 mm, and the average thickness is 4 to 5 mm.
- It’s less likely to be injured because:
- It is firmly attached to the popliteus muscle and to the ligament of Wrisberg or of Humphry, which make it follows the lateral femoral condyle during rotation.
- Acute lateral meniscus tears are more common associated with Anterior Cruciate Ligament Injury.
The menisci follow the tibial condyles during flexion and extension, but during rotation they follow the femur and move on the tibia.
In case of meniscal injuries, the special tests used to examine the knee for meniscal injury are:
- Lateral McMurray Test for lateral meniscus.
- Medial McMurray Test for medial meniscus.
- Thessaly test.
- Ege’s Test.
- Apley grinding Test.