Functions of the Meniscus

For Medical Students

The Principle

A structure between two bones can do several things at once. It can spread load, damp impact, guide movement, help lubrication and report position.

The menisci do all five. They are not a cushion, which is the commonest wrong description, because a cushion absorbs load and a meniscus distributes it.

Ranking the five matters. Load distribution is the function whose loss causes the disease, and the others are real and secondary.

At the Knee

Load transmission is the main job. The wedge shape fills the space between a curved femoral condyle and a flatter tibia, so contact happens over a large area. 3.5.1 covers contact area.

Shock absorption is the second. Meniscal tissue is viscoelastic and deforms under fast load, which is part of the limb's damping. 3.6.6 covers it.

Stability is the third. The menisci deepen the surfaces and the medial posterior horn acts as a secondary restraint to anterior translation. 3.2.10 covers stability.

Lubrication and proprioception are the fourth and fifth, and both are supported and smaller. 3.6.7 and 3.6.8 cover them.

What Changes It

Whether the ring is intact and anchored, which decides whether any of the five work. 3.6.2 covers the ring.

Which meniscus, since the lateral contributes more to its compartment's contact area.

Flexion angle, which changes how much load passes through the menisci.

Tissue quality, since a degenerate meniscus carries tension less well than it looks able to.

Clinical Relevance

Calling the meniscus a shock absorber or a cushion leads to the wrong conclusions about resection, which is why the description matters.

Losing a meniscus removes a load distributor, and the compartment degenerates. 6.37 covers meniscal deficiency.

A meniscus can fail at any of the five functions, and the examination findings differ by which. Section 4 covers the tests.

Preservation is preferred because the functions cannot be replaced individually. Section 6 covers management.

MRCS Level

The Principle

Every function depends on one structural condition: a continuous ring anchored at both ends. Compression is converted to circumferential tension, and tension needs both an intact hoop and two attachments. 3.6.2 covers the mechanism.

That condition is why function and appearance separate. A meniscus can look complete on imaging and carry no tension, and a repaired one can look imperfect and work.

It also explains the tear patterns that matter. A tear across the fibres costs function; a tear along them may not.

At the Knee

Conventional teaching gives the menisci roughly half of the load transmitted across the tibiofemoral joint in extension, rising substantially in flexion as contact moves onto the posterior horns. 3.6.5 covers load sharing.

The lateral meniscus matters more to its compartment, because the lateral tibial plateau is convex and offers no concavity of its own. 2.6.1 covers the anatomy.

The medial meniscus is more firmly attached and translates less, which makes it a better secondary restraint and more vulnerable to a tear when the knee translates. 2.5.1 covers it.

Proprioceptive and lubricating roles are supported by anatomical and laboratory work and are not quantified in the way load transmission is.

What Changes It

Ring continuity and root attachment, which are the structural conditions.

Flexion angle, which shifts the share the menisci carry.

Degeneration, which reduces the tissue's tensile capacity without changing its outline.

Previous resection, by the amount and the location.

How It Is Measured

Cadaveric contact studies with pressure sensors measure the load transmission role directly, in a specimen under a chosen load.

Tensile testing of meniscal strips measures the tissue's circumferential and radial properties, in excised tissue.

Histological and immunohistochemical work demonstrates mechanoreceptors, which establishes the presence of a sensory role rather than its magnitude.

No clinical measurement of any of the five functions exists in a patient, so function is inferred from structure. 5.6 covers imaging.

Clinical Relevance

Judge a meniscus by whether the ring is continuous and anchored rather than by how much tissue is present.

Expect a degenerate meniscus to carry less tension than its outline suggests.

Treat the lateral meniscus as the more important one to its compartment, against the frequency of injury.

Infer function from structure, and say that is what you are doing.

FRCS Level

At the Knee

Treat the five functions as a package that cannot be restored selectively. A repair that restores the ring restores all five to some degree; a device that restores area restores one.

That is the mechanical argument for repair over substitution, and for substitution over nothing. The ordering follows from the structure rather than from the outcome data, and the outcome data agrees.

Conventional teaching holds that meniscal function is not restored by any current substitute to the level of a repaired native meniscus, which is why the decision taken at the first operation is the one that matters. 6.43 covers transplantation problems.

What Changes It

Whether the ring can be restored at the first operation, which decides everything later.

Root integrity, which is the structural condition for tension. 3.6.9 covers it.

Alignment, which decides whether a working meniscus is protected or overloaded. 3.13 covers it.

Cartilage state at the time, since restoring function to a damaged surface achieves less.

How It Is Measured

Paired cadaveric studies comparing intact, torn, repaired and substituted states are the standard for a mechanical claim about function.

Long term cohorts measure joint preservation, which is the clinical form of the same question over a decade.

Second look arthroscopy and imaging measure healing rather than restored tension.

Nothing measures restored meniscal function in a patient, which is the standing gap in this whole field.

Clinical Relevance

Repair at the first operation wherever the ring can be restored, because the decision is not repeatable.

Address root integrity and alignment alongside the meniscus, since both decide whether it works.

Explain that healing on imaging is not restored function.

Rank repair above substitution and substitution above nothing, on structural grounds.