Gross Anatomy

For Medical Students

Structure and Location

The lateral meniscus is a fibrocartilaginous ring on the lateral tibial plateau. Seen from above it is almost a closed O rather than the medial meniscus's open C, because its two horns attach close together.

It covers more of its plateau than the medial meniscus covers of its own, conventionally given as about 75 per cent of the lateral articular surface.

In cross section it is the same wedge as the medial: thick peripherally, thin at the free edge, concave above and flat below. Its body is of fairly even width around the ring rather than broadening posteriorly.

Relations

Above: the lateral femoral condyle. Below: the lateral tibial plateau, which is convex in the sagittal plane, so the meniscus is supplying more congruence here than on the medial side.

Peripherally: the capsule, but with an important gap. At the popliteus hiatus the tendon crosses between the meniscus and the capsule, so the meniscus has no capsular attachment over that length.

Posteriorly: the popliteomeniscal fascicles tether the posterior part to the popliteus tendon, and the meniscofemoral ligaments run from the posterior horn to the medial femoral condyle. 2.6.2 and 2.6.3 cover both.

Anteriorly: the transverse intermeniscal ligament joins its anterior horn to the medial meniscus.

Function

The same hoop mechanism as the medial meniscus, described on 2.5.4. Compression of the wedge is resisted by circumferential fibres anchored at the horns.

The lateral meniscus does more congruence work, because the surface under it is convex rather than concave. Take it away and the lateral compartment loses more than the medial compartment loses without its own.

It is also far more mobile. The horns are close together, the capsular attachment is interrupted at the hiatus, and the coronary ligaments are longer. It translates with the femoral condyle rather than being loaded in place.

Clinical Relevance

Mobility protects it. The lateral meniscus is torn less often than the medial in the intact knee, because it moves out of the way.

Losing it costs more. Lateral meniscectomy is associated with faster and more severe cartilage loss than medial meniscectomy, and the convex plateau underneath is the reason.

It is the meniscus that can be congenitally discoid, a variant in which the meniscus covers most or all of the plateau. Conventional teaching puts the prevalence at a few per cent, with wide variation between populations.

MRCS Level

Structure and Location

Compare it to the medial meniscus feature by feature. The horns attach close together rather than far apart, so the ring is nearly closed. The body is of even width rather than broadening posteriorly. The coronary ligaments are longer, so the periphery is less tightly held. And the capsular attachment is absent at the popliteus hiatus.

The posterior horn has two further attachments the medial side does not: the popliteomeniscal fascicles to the popliteus tendon, and one or both meniscofemoral ligaments to the medial femoral condyle.

The anterior horn attaches in the anterior intercondylar area close to and often overlapping the anterior cruciate tibial footprint. The posterior horn attaches immediately in front of the posterior cruciate's attachment and lateral to the medial meniscus's posterior root. 2.6.4 covers both.

Relations

The popliteus hiatus is the defining relation. The tendon passes from its sulcus on the lateral femoral condyle, through a gap in the capsule, to the muscle belly. Over that length the meniscus is held not by capsule but by the fascicles.

That gap is also a route: a tear at the posterolateral periphery can extend into a region with no capsular attachment and therefore no tissue to repair to.

Laterally, outside the capsule, lie the lateral collateral ligament and the posterolateral corner structures, which do not attach to this meniscus. That is the opposite of the medial arrangement and is the second major difference between the two sides.

The inferior lateral genicular artery runs circumferentially just outside the peripheral border and supplies the perimeniscal plexus on this side.

Blood Supply and Innervation

The supply is the same arrangement as described on 2.5.3, derived here from the lateral genicular arteries, with the same peripheral penetration and the same three zones.

The hiatus region is a relative watershed, because the capsular tissue that carries the plexus is absent there. Tears in that region behave as if more central than their position suggests.

Innervation follows the vessels, with mechanoreceptors at the horns. The popliteomeniscal fascicles carry receptors and are proposed as part of the dynamic control of meniscal position.

Function

Load sharing follows the same hoop mechanism, with the extra demand of a convex tibial surface beneath. The lateral meniscus is doing more of the congruence work and is therefore less dispensable, which is the opposite of what its lower tear rate suggests.

Mobility is the second function. The posterior horn translates posteriorly with the femoral condyle through flexion, and the fascicles and the popliteus control that movement rather than preventing it.

The meniscofemoral ligaments pull the posterior horn forwards as the knee extends, which is a second mechanism for keeping the meniscus under the condyle. 2.6.3 covers them.

Clinical Relevance

Lateral meniscectomy has worse long term consequences than medial, and the convex plateau is the anatomical explanation. That asymmetry should change the threshold for resection on this side.

A tear at the popliteus hiatus may be unrepairable because there is nothing to repair to, and recognising the position matters more than measuring the tear.

Discoid lateral meniscus is a variant of shape with an associated instability of attachment, and the Wrisberg type lacks the posterior capsular attachment entirely. Classification and management belong to Sections 5, 6 and 10.

Because the anterior horn attachment can overlap the anterior cruciate footprint, cruciate tunnel placement can injure it, in the same way as the medial anterior root.

FRCS Level

Relations

The posterolateral periphery is the region where the usual rules do not apply. There is no capsular attachment at the hiatus, the vascular tissue is interrupted, and the fascicles are the only tether. A tear there is assessed on what is left to fix rather than on its distance from a margin.

The popliteus tendon is in the way of instruments approaching the posterolateral periphery, which is both a hazard and a landmark.

Function

The lateral meniscus is mobile by design, so stability of attachment and freedom of movement are both normal findings and the line between them is a judgement. A hypermobile lateral meniscus is a recognised entity and 2.6.2 covers the anatomy.

Because the compartment depends on the meniscus for congruence, restoring the meniscus matters more here. That is the anatomical case for lateral allograft transplantation being considered earlier than medial.

Clinical Relevance

Preserve lateral meniscal tissue more aggressively than medial. The anatomy, not the evidence, is the primary argument: the compartment has no concavity of its own.

In a young patient after lateral meniscectomy, allograft transplantation is a legitimate consideration and Section 7 owns the indications.

At arthroscopy, assess lateral meniscal mobility deliberately rather than incidentally. Excessive translation with an intact meniscus points at the fascicles.

The coverage proportion and the discoid prevalence on this page are standard teaching values, registered and unchecked. The discoid figure in particular varies several fold between populations.