The medial meniscus is a crescent-shaped wedge of fibrocartilage that sits on the inner (medial) side of the knee, resting on the tibial plateau between the femur and tibia. It covers roughly half of the medial tibial plateau and is slightly thicker on average than its lateral counterpart, though both share a similar overall volume. What makes the medial meniscus anatomically distinctive is not just its shape but its anchoring system, internal fiber architecture, regionally variable blood supply, and limited mobility compared with the lateral meniscus. Understanding these structural details helps explain why certain tears heal well and others do not, and why the posterior horn is the site that gives surgeons the most trouble.
Overall Shape and Dimensions
Viewed from above, the medial meniscus traces a broad C or semicircle. Its posterior horn is wider than its anterior horn, giving the structure an asymmetric profile. In cross-section, it is wedge-shaped: thick at the outer (peripheral) rim and tapering to a thin, free inner edge. MRI-based measurements in healthy men found the medial meniscus covers about 50% of the medial tibial plateau, compared with roughly 59% plateau coverage by the lateral meniscus. Despite this difference in footprint, the two menisci have nearly identical volumes, each averaging around 2.4 mL. The medial meniscus compensates for its smaller footprint by being slightly thicker, with a mean thickness of about 2.8 mm versus 2.7 mm for the lateral side.1PubMed Central. Morphometric differences between the medial and lateral meniscus in healthy men – a three-dimensional analysis using magnetic resonance imaging
Internal Collagen Architecture
The medial meniscus is not a uniform slab of cartilage. Its mechanical strength comes from two interlocking collagen networks. The primary network consists of thick bundles of collagen fibers running circumferentially, following the C-shaped curve of the meniscus from one root attachment to the other. These circumferential fibers are the ones that generate hoop stress when the knee is loaded, converting compressive force from the femur into tensile force along the length of the meniscus. Imaging of meniscal tissue confirms this arrangement of circumferential bundles paired with radially oriented “tie fibers” that run perpendicular to them.2PubMed Central. Regional and fiber orientation dependent shear properties and anisotropy of bovine meniscus
Those radial tie fibers deserve special attention because they are what hold the circumferential bundles together, preventing them from splaying apart under load. Detailed three-dimensional imaging reveals that tie fibers are more complex than simple cross-struts. They come in at least three forms: broad overlapping sheets, discrete bundles, and finer individual fibers. The sheets often stack with their fiber rows oriented at different angles, creating an interwoven structure that subdivides the circumferential fascicles into progressively smaller groups.3PubMed Central. Tie-fibre structure and organization in the knee menisci This layered, interlocking design is part of what makes meniscal tissue so difficult to replicate with synthetic materials.
The radial tie fiber network also changes over a lifetime. In fetal menisci, these fibers are relatively sparse and uniform. As the skeleton matures through childhood and into adulthood, the tie fibers become denser, thicker, and more heterogeneous, reflecting the increasing mechanical demands placed on the tissue.4PubMed Central. Structure, function, and defect tolerance with maturation of the radial tie fiber network in the knee meniscus
What the Meniscus Is Actually Made Of
The composition of the medial meniscus varies dramatically from its outer rim to its thin inner edge, and these regional differences track with the different mechanical jobs each zone performs. The outer zone is almost entirely collagen (about 93% by dry weight), with only around 2% glycosaminoglycans, the sugar-protein molecules that attract and hold water. The inner zone is quite different: roughly 76% collagen and 8% glycosaminoglycans. The middle zone falls in between.5PubMed. Glycosaminoglycans and proteoglycans from different zones of the porcine knee meniscus This gradient makes biological sense. The outer zone, anchored to the capsule and rich in circumferential collagen, resists tension. The inner zone, where compressive forces from the femoral condyle dominate, is enriched with water-attracting molecules that help it resist being crushed, much as articular cartilage does. Decellularized tissue analysis confirms the same pattern: the inner meniscal matrix contains the greatest glycosaminoglycan content and the least collagen.6Biomedical Materials. Regional-specific meniscal extracellular matrix hydrogels and their effects on cell–matrix interactions of fibrochondrocytes
The dominant glycosaminoglycan throughout the meniscus is chondroitin sulfate, accounting for about 80% of the total in the inner zone. Dermatan sulfate is the second most abundant, and hyaluronic acid makes up a small fraction. The outer zone has proportionally more dermatan sulfate and hyaluronic acid relative to chondroitin sulfate.7PubMed. Glycosaminoglycans and proteoglycans from different zones of the porcine knee meniscus
Blood Supply and the Three-Zone System
One of the most clinically consequential features of the medial meniscus is its uneven blood supply, because blood vessels are what make tissue repair possible. The peripheral rim receives blood from a network branching off the genicular arteries that supply the knee capsule. Moving inward, the blood supply thins out and eventually disappears. Clinicians divide this gradient into three zones: the peripheral “red-red” zone (well-vascularized), a transitional “red-white” zone, and the inner “white-white” zone (avascular). A tear in the red-red zone can heal, sometimes with surgical assistance. A tear in the white-white zone has essentially no blood-borne healing capacity.
Recent three-dimensional micro-CT imaging has added more granularity to this picture. In the medial meniscus, the perimeniscal zone (zone 0, the very outermost edge) distributes its blood vessels unevenly across layers: roughly 39% in the superior (top) layer, 41% in the intermediate (middle) layer, and only 20% in the inferior layer near the tibia. Deeper into the meniscus body, the intermediate layer consistently carries the least blood vessel volume.8PubMed Central. Vascularization Characteristics of the Different Meniscal Layers: Three-Dimensional Assessment With Micro-CT This means the vascular zones are not simple concentric rings; the density of vessels also varies by depth within the same cross-sectional slice.
How the Blood Supply Changes with Age
The vascular architecture of the meniscus is not static. Fetal menisci are highly cellular and penetrated by blood vessels throughout. By the 29th week of gestation, vessels have already retreated to the periphery, setting the stage for the adult pattern.9Translational Research in Anatomy. An exploratory study of the histomorphogenesis and zonal vascular changes in the human fetal medial meniscus After birth, vessel density continues to decline. A study examining menisci across age groups from birth to 80 years found a significant negative trend in overall vascular density with increasing age. Beyond the first two decades of life, no vasculature was found in the red-white zone at all, and the white-white zone was avascular at every age.10PubMed. Age-Related Changes in the Microvascular Density of the Human Meniscus This progressive vascular loss may partially explain why meniscal tears become harder to repair in older patients, even when the tear location is technically in the peripheral zone.
Cell density and proteoglycan content also shift during development. Younger menisci are packed with cells and blood vessels; as the skeleton matures, cell counts drop and the proteoglycan-to-collagen ratio increases, reflecting a tissue that is transitioning from a growing, remodeling structure to a load-bearing one.11PubMed. Changes in Matrix Components in the Developing Human Meniscus
Root Attachments
The medial meniscus is anchored to the tibia at two points called its “roots.” The anterior root attaches in front of the tibial eminence (the bony ridge at the center of the tibial plateau), and the posterior root attaches behind and slightly lateral to it. These roots are the anchor points for the circumferential collagen fibers, and without them, the meniscus cannot generate hoop tension. A root tear is functionally similar to a total meniscectomy in terms of the biomechanical consequences for the joint.
The posterior root has been the focus of extensive anatomical study because it tears more often than the anterior root and because its precise location matters for surgical repair. Cadaveric measurements show its footprint is oval, measuring roughly 8.3 mm front-to-back and 4.3 mm side-to-side, and it sits about 6.9 mm from the tibial insertion of the posterior cruciate ligament.12Revista Colombiana de Ortopedia y TraumatologÃa. Anatomical Study of the Posterior Root of Medial Meniscus in Human Knee A separate quantitative analysis using a coordinate system centered on the medial tibial eminence apex found the posterior root center about 11.5 mm away from that landmark, positioned roughly 9.6 mm posterior and slightly lateral to it, with the nearest edge of the posterior cruciate ligament’s tibial attachment about 8.2 mm away.13PubMed. Qualitative and quantitative anatomic analysis of the posterior root attachments of the medial and lateral menisci Surgeons use these landmarks during arthroscopic repair to place tunnels or anchors as close to the native attachment as possible.
Advanced 3D MRI sequences now allow interactive visualization of these root structures in living patients, which helps with pre-surgical planning and with diagnosing subtle partial root tears that standard two-dimensional imaging can miss.14European Journal of Radiology. An anatomical study of normal meniscal roots with isotropic 3D MRI at 3 T
The Peripheral Attachments and Ramp Region
Besides its roots, the medial meniscus is secured along its outer rim to the joint capsule and the tibia through a series of softer attachments. The meniscotibial ligament (also called the coronary ligament) tethers the meniscus to the tibial rim. When this ligament tears in isolation, the meniscus can float slightly above the tibial plateau on imaging, a pattern distinct from a meniscal body tear.15Skeletal Radiology. Meniscotibial (coronary) ligament tears
The region where the posterior horn of the medial meniscus meets the capsule and tibial rim is known as the “ramp” zone, and it has become a major focus in sports medicine because ramp lesions (tears at this junction) frequently accompany anterior cruciate ligament injuries. Cadaveric dissections measured the posterior meniscocapsular attachment at an average length of about 20 mm; it attaches to the posterior horn at roughly a third of the way up from the bottom of the meniscal wall. The meniscotibial ligament’s tibial footprint sits about 5.9 mm below the edge of the articular cartilage on the posterior medial plateau.16PubMed. Quantitative and Qualitative Assessment of the Posterior Medial Meniscus Anatomy: Defining Meniscal Ramp Lesions
Histological examination of these attachments reveals loose, partially oriented collagen fibers, a scattering of fibroblasts and fat cells, and several small blood vessels at the junction. One study found that the meniscocapsular and meniscotibial attachments share a common insertion site on the posterior horn and look similar under the microscope, though the meniscocapsular tissue appeared denser.17PubMed Central. Ramp Lesions of the Posterior Segment of the Medial Meniscus: What Is Repaired? A Qualitative Histological Study of the Meniscocapsular and Meniscotibial Attachments This shared anatomy is relevant to surgeons performing ramp lesion repairs, because a suture through the “ramp” region is passing through both tissues simultaneously.
Hoop Stress and Load Bearing
The medial meniscus absorbs and distributes load using a mechanism called hoop stress. When the curved surface of the femoral condyle presses down, the wedge-shaped meniscus tries to squirt outward. The circumferential collagen fibers, anchored at both roots, resist this outward displacement by converting the downward compression into tension along their length, like a hoop around a barrel. As long as the fibers and root attachments are intact, the meniscus spreads load over a wide area of the tibial plateau.
Disruption of this system has measurable consequences. Biomechanical modeling of the osteoarthritic knee found that hoop stress in the posterior horn of the medial meniscus was about 83% greater than in a healthy joint, while the anterior horn saw only an 11% increase.18PubMed Central. Biomechanics of the medial meniscus in the osteoarthritic knee joint This disproportionate stress on the posterior horn helps explain why that region degenerates faster. Radial tears, which cut across the circumferential fibers, are especially damaging because they reduce the cross-sectional area available to transmit hoop tension. The stress concentrates at the tear apex, and the direction of hoop stress can actually reverse at the tear site, providing a mechanical reason for why radial tears tend to propagate once they start.19PubMed Central. Finite element analysis of medial meniscus tears and related surgical techniques with biomechanical validation Posterior root tears similarly destroy the anchor point for hoop tension and are considered a biomechanical equivalent of removing the meniscus entirely.20PubMed Central. Why Hoop Tension Matters: A Biomechanical Perspective on Medial Meniscus Posterior Root Tears-A Narrative Review
Movement During Knee Flexion
The medial meniscus is not bolted in place. It glides posteriorly on the tibial plateau as the knee bends, tracking the backward roll of the femoral condyle. But its range of motion is relatively modest. MRI analysis during deep knee flexion measured about 3.3 mm of posterior translation for the medial meniscus, compared with 8.2 mm for the lateral meniscus.21PubMed. Magnetic resonance image analysis of meniscal translation and tibio-menisco-femoral contact in deep knee flexion A systematic review of the highest-quality studies confirmed this finding: the lateral meniscus consistently translates more than the medial meniscus during flexion.22PubMed. Meniscal translation during knee flexion: what do we really know?
The medial meniscus’s limited mobility is a direct consequence of its attachments. Its broader capsular connection, longer meniscotibial ligament, and attachment to the deep fibers of the medial collateral ligament all act as leashes. This constrained movement protects the medial compartment but also makes the posterior horn vulnerable: because the meniscus cannot slide out of the way, it absorbs more shear force during activities like deep squatting and pivoting.
Nerve Supply and Proprioception
The meniscus is not just a passive spacer. Its outer portions contain nerve fibers, and studies of human menisci have found that mechanoreceptors in the medial compartment of the knee are concentrated specifically in the anterior and posterior horns of the medial meniscus.23PubMed. Evaluation of the neurosensory function of the medial meniscus in humans These receptors detect mechanical deformation and likely contribute to the knee’s sense of joint position. This finding has practical implications: a meniscectomy that removes horn tissue may not just change the mechanics of the knee but could also reduce the joint’s proprioceptive feedback, contributing to the instability some patients report after surgery even when the ligaments are intact.
The Discoid Medial Meniscus
Most anatomical descriptions assume a normal crescent shape, but a small percentage of people are born with a “discoid” meniscus, a thickened, disc-like structure that covers most or all of the tibial plateau. A discoid lateral meniscus is a well-known variant found in roughly 3 to 5% of the population, but a discoid medial meniscus is far rarer, reported at only 0.03 to 0.3%.24Journal of Clinical Imaging Science. Ipsilateral Medial and Lateral Discoid Menisci: A Rare Combination of Infrequent Anatomic Variants Because of its rarity, a discoid medial meniscus is often discovered incidentally on MRI or during arthroscopy for other reasons. It can be asymptomatic, but when it is unstable or torn, it may cause mechanical symptoms like clicking, locking, or a feeling that the knee is “giving way.” Treatment depends on how much of the meniscus is abnormal and whether it is causing problems, but surgeons generally try to reshape the disc into something closer to a normal crescent (a procedure called saucerization) rather than removing it entirely.
How the Medial Meniscus Develops Before Birth
The adult pattern of a well-organized, partially vascularized meniscus is the end point of a developmental sequence that begins early in fetal life. In the earliest stages, the meniscus is densely packed with cells and fully penetrated by blood vessels. The collagen fibers are initially disorganized but become progressively more ordered as gestation advances. By the 29th week, blood vessels have already withdrawn to the periphery, foreshadowing the red-white-white zone system of the adult.25Translational Research in Anatomy. An exploratory study of the histomorphogenesis and zonal vascular changes in the human fetal medial meniscus Cell density continues to drop after birth, and the ratio of proteoglycans to collagen rises as the tissue shifts from a building phase to a load-bearing phase.26PubMed. Changes in Matrix Components in the Developing Human Meniscus This trajectory is worth knowing because it means the healing-friendly environment that exists in a young child’s meniscus is progressively lost with skeletal maturity, not abruptly switched off at a particular age.