The medial meniscus is C-shaped and fixed; the lateral is more circular and mobile
Mnemonic
“The medial meniscus is C-shaped and captured; the lateral is O-shaped and free”:
- Medial - larger, more C shaped, and firmly attached to the medial collateral ligament and the capsule, so it is less mobile and tears more often
- Lateral - more circular, separated from the lateral collateral ligament by the popliteus tendon, so it is more mobile and tears less
“The medial meniscus is part of the unhappy triad” precisely because of that attachment: a valgus force with rotation tears the anterior cruciate ligament, medial collateral ligament and medial meniscus together.
The menisci are avascular centrally and vascular only in the outer third (the red zone), which is why peripheral tears can be repaired while central tears are trimmed.
Their function is load distribution, increasing the contact area and reducing contact stress, which is why meniscectomy accelerates osteoarthritis, and why repair is preferred where possible.
Expansion
- Medial meniscus - a wider C shape, firmly attached to the medial collateral ligament and joint capsule, so it is less mobile and more often torn
- Lateral meniscus - a tighter, almost circular O shape, not attached to the lateral collateral ligament, so it is more mobile and less often injured
Both deepen the tibial surface and cushion load between the femur and tibia.