Gross Anatomy

For Medical Students

Structure and Location

The medial meniscus is a crescent of fibrocartilage lying on the medial tibial plateau. Seen from above it is a long, open C, broader at the back than the front.

In cross section it is a wedge: thick at its peripheral border and tapering to a thin free edge centrally. The upper surface is concave to receive the femoral condyle and the lower surface is flat on the plateau.

Its two ends, the anterior and posterior horns, attach to the tibia in the intercondylar area. The posterior horn attachment is further apart from the anterior one than on the lateral side, which is why the C is more open.

Relations

Above: the medial femoral condyle. Below: the medial tibial plateau.

Peripherally: the capsule, and through it the deep layer of the medial collateral ligament, which attaches to the meniscus itself as well as to bone above and below. That attachment is called the meniscotibial and meniscofemoral part of the deep collateral, and it is the reason this meniscus is tethered.

Anteriorly: the transverse intermeniscal ligament, joining the anterior horn to the anterior horn of the lateral meniscus.

Posteromedially: the semimembranosus expansion reaches the capsule close to the posterior horn.

Function

The meniscus turns a flat tibial surface into a concave one, so a convex femoral condyle sits in a socket rather than on a plate.

It spreads load over a wider area than bare cartilage contact would, and it resists being squeezed outwards by that load because its circumferential fibres are anchored at both horns.

It also contributes to stability. Because the posterior horn is a wedge behind the femoral condyle, it resists the condyle translating backwards on the tibia, which means it acts as a secondary restraint to anterior translation of the tibia.

Clinical Relevance

Being tethered to the deep collateral ligament makes this meniscus less mobile than the lateral one, and less able to move out of the way of a load. It is torn more often.

The posterior horn carries most of the load in flexion and is the commonest site of tear.

Because the posterior horn is a secondary restraint to anterior translation, a knee with a torn anterior cruciate loads it more, which is why medial posterior horn tears are common in chronic cruciate deficiency.

MRCS Level

Structure and Location

Describe the meniscus in three parts and three dimensions. Anterior horn, body, posterior horn. Peripheral border thick and convex, free edge thin and concave, upper surface concave and lower surface flat.

The medial meniscus covers a smaller proportion of its plateau than the lateral does of its own, conventionally given as about 60 per cent of the medial articular surface.

The posterior horn is wider than the anterior, so the wedge is deepest where the load in flexion is greatest.

Horn attachment positions are described on 2.5.7. The relevant gross point is that they sit in the intercondylar area rather than on the articular surface, and the anterior horn attachment is anterior to the anterior cruciate's tibial footprint.

Relations

Peripheral attachment is through the coronary, or meniscotibial, ligament to the tibia just below the articular margin, and through the meniscofemoral part of the deep collateral to the femur. Those two short structures are what fix this meniscus.

The superficial medial collateral ligament lies outside the capsule and does not attach to the meniscus. Confusing the superficial and deep layers is the commonest error in describing this region.

Posteromedially the posterior oblique ligament and the semimembranosus reinforce the capsule next to the posterior horn.

The transverse intermeniscal ligament crosses in front, and the anterior horn also has fibrous continuity with the anterior intercondylar area and the fat pad.

Blood Supply and Innervation

The perimeniscal capillary plexus, derived from the medial genicular arteries, surrounds the peripheral border and sends branches into the outer part of the meniscus. Conventional teaching gives the vascular penetration as the peripheral 10 to 30 per cent of the width. 2.5.3 covers the zones and what they mean.

The inner part is avascular and is nourished by diffusion from synovial fluid.

Innervation follows the same route: nerve fibres and mechanoreceptors are present in the peripheral third and in the horns, and the inner part is uninnervated. That is why a peripheral tear hurts and a central degenerative change may not.

Function

Load transmission depends on hoop stress. Compression of the wedge drives it peripherally, the circumferential collagen bundles resist that, and the horn attachments take the resulting tension. Remove either horn attachment and the hoop is broken, and the meniscus stops transmitting load even though it is still present.

Conventional teaching has the menisci transmitting about half of the load across the joint in extension and a greater proportion in flexion.

Secondary stabilisation comes from the posterior horn acting as a wedge. The medial meniscus contributes more to this than the lateral because it is less mobile.

3.6 owns the quantitative mechanics.

Clinical Relevance

A root tear and a radial tear both break the hoop, so both behave like a functional meniscectomy even where most of the tissue remains.

The avascular inner portion does not heal, which is the anatomical basis of repairing peripheral tears and resecting central ones.

A tethered meniscus is loaded rather than displaced, which is why medial tears are commoner and why a medial meniscal tear in a young patient should prompt a question about the cruciate.

Extrusion of the meniscus beyond the tibial margin indicates loss of hoop integrity and is a finding about function rather than about position alone.

FRCS Level

Relations

The relations that decide repairability are peripheral: the capsule, the coronary ligament and the vascular plexus within them. A tear within that zone has a blood supply to heal with and tissue to suture to; one central to it has neither.

The posteromedial corner is the access problem. The posterior horn sits in a tight space bounded by the femoral condyle above, the plateau below and the capsule behind, and the structures outside that capsule include the saphenous nerve and vein.

Function

Meniscal function is an all or nothing property of the hoop rather than a graded property of the tissue. That single fact reorganises how tears are thought about: the question is not how much meniscus remains but whether the ring still transmits tension.

It is also why root repair has become a separate operation from tear repair. Restoring the attachment restores the mechanism; debriding the tear does not.

Clinical Relevance

In a young patient with a repairable peripheral tear, repair preserves the hoop and resection does not. The anatomy decides the case before the evidence does.

In chronic anterior cruciate deficiency the posterior horn is working as a primary restraint it was not designed to be, and a tear there changes the reconstruction plan rather than being incidental to it.

Meniscal extrusion with an intact meniscus points at the root, and the root is reachable. 2.5.7 covers it.

Every dimension on this page is written from standard teaching and registered as unchecked. The coverage proportion and the load share in particular are quoted differently by different authors.