Menisci (Medial, Lateral)

The menisci of the knee are two fibrocartilaginous structures positioned between the femoral condyles and the tibial plateau. They are known as the medial meniscus and lateral meniscus. Each meniscus has a thick peripheral border attached to the joint capsule and a thin free inner margin that projects into the joint.^[1][2]

The menisci improve the congruity between the rounded femoral condyles and the relatively shallow articular surfaces of the tibia. They also distribute loads across the tibiofemoral joint, contribute to shock absorption, assist joint lubrication, and participate in stabilization of the knee.

Although the two menisci have the same general organization, they differ considerably in shape, attachments, mobility, and relationships. The medial meniscus is more C-shaped and relatively firmly attached, particularly to the medial joint capsule and deep medial collateral ligament. The lateral meniscus is more nearly circular, has no direct attachment to the lateral collateral ligament, and is generally more mobile.

Location

The medial and lateral menisci lie within the tibiofemoral joint between the corresponding femoral condyles and tibial condyles. They rest on the superior articular surface of the tibia and move in relation to both the tibia and femur during knee motion.

Each meniscus occupies the peripheral portion of its tibial compartment. The outer border is thick and attached to surrounding capsular structures, while the inner border is thin and free within the joint.

In cross-section, a meniscus is approximately wedge-shaped, with its thicker base directed toward the joint capsule and its thinner edge directed toward the central portion of the tibial plateau.

General Structure

The menisci consist primarily of fibrocartilage containing a highly organized collagen network. Circumferentially oriented collagen fibers form an important structural framework that allows the menisci to resist forces generated during weight bearing.

Radially oriented fibers help bind the circumferential fibers together and resist longitudinal splitting. This organization allows compressive loads applied to the meniscus to be converted partly into circumferential tensile forces, often described as hoop stresses.

Each meniscus can be described as having:

• Anterior horn: The anterior end attached to the tibial intercondylar region.
• Body: The intermediate portion extending around the tibial plateau.
• Posterior horn: The posterior end attached to the tibial intercondylar region.
• Peripheral border: The thick outer margin related to the joint capsule.
• Free inner border: The thin central edge facing the intercondylar region.
• Superior surface: Concave to accommodate the femoral condyle.
• Inferior surface: Relatively flat and related to the tibial plateau.

Medial Meniscus

The medial meniscus occupies the medial tibiofemoral compartment. It is typically described as C-shaped or semicircular, with a relatively wide separation between its anterior and posterior horns.

Its peripheral border is firmly associated with the medial joint capsule. The deep fibers of the medial collateral ligament are closely related to and attached to the peripheral medial meniscus through the meniscofemoral and meniscotibial portions of the deep medial collateral complex.

These attachments restrict the mobility of the medial meniscus compared with the lateral meniscus. This difference in mobility is important in understanding the mechanical behavior and injury patterns of the two structures.

Attachments of the Medial Meniscus

The anterior and posterior horns of the medial meniscus are firmly anchored to the tibia within the intercondylar region.

The anterior horn attaches to the anterior intercondylar area of the tibia. Its precise relationship with the anterior horn of the lateral meniscus and the anterior cruciate ligament varies according to the arrangement of the tibial attachment sites.

The posterior horn attaches within the posterior part of the tibial intercondylar region. The posterior root attachment is particularly important mechanically because it anchors the meniscus and allows circumferential hoop stresses to be transmitted through the tissue.

The peripheral margin is attached to the joint capsule and medial collateral complex. Inferiorly, short coronary or meniscotibial ligaments connect the meniscus to the margin of the tibial plateau.

Lateral Meniscus

The lateral meniscus occupies the lateral tibiofemoral compartment. It is more nearly circular than the medial meniscus and covers a relatively large proportion of the lateral tibial articular surface.

Its anterior and posterior horns lie relatively close together within the intercondylar region. Like the medial meniscus, these horns are anchored to the tibia by strong root attachments.

The lateral meniscus is generally more mobile than the medial meniscus. One important reason is that it is not directly attached to the lateral collateral ligament. The popliteus tendon passes between the lateral meniscus and the LCL, interrupting the capsular attachment in the posterolateral region.

Attachments of the Lateral Meniscus

The anterior horn of the lateral meniscus attaches to the anterior intercondylar area of the tibia, close to the tibial attachment of the anterior cruciate ligament.

The posterior horn attaches within the posterior intercondylar region. It also has important ligamentous connections with the femur through the meniscofemoral ligaments.

The peripheral border is attached to the joint capsule except where the popliteus tendon passes between the meniscus and capsule posterolaterally. This region is associated with the popliteal hiatus.

Meniscotibial attachments also connect the lateral meniscus to the tibial plateau while permitting greater mobility than is generally present on the medial side.

Comparison of the Medial and Lateral Menisci

Feature	Medial Meniscus	Lateral Meniscus
Shape	C-shaped or semicircular	More nearly circular
Mobility	Relatively less mobile	Relatively more mobile
Collateral ligament relationship	Closely related to deep MCL	No direct attachment to LCL
Popliteus relationship	No popliteal hiatus	Popliteus tendon passes adjacent to meniscus through popliteal hiatus
Horn separation	Relatively wide	Anterior and posterior horns closer together
General injury tendency	More frequently injured	Greater mobility provides some protection from certain mechanical stresses

Meniscal Roots

The anterior and posterior horns attach firmly to the tibial plateau through meniscal roots. These attachments anchor the menisci to the tibia and are fundamental to their mechanical function.

When the knee is loaded, compression of a meniscus tends to displace it outward from beneath the femoral condyle. The root attachments prevent excessive extrusion and allow circumferential fibers to develop tension.

A root injury can therefore impair meniscal function even when much of the fibrocartilaginous body remains physically present. Loss of effective root fixation reduces the ability of the meniscus to distribute load normally across the tibial plateau.

Transverse Ligament of the Knee

The transverse ligament of the knee, also called the transverse intermeniscal ligament, commonly connects the anterior horns of the medial and lateral menisci.

Its size and exact attachment pattern vary considerably. In some individuals it is well developed, while in others it may be small or absent.

The ligament provides a connection between the anterior portions of the two menisci and may help coordinate their movements during knee motion.

Meniscofemoral Ligaments

The posterior horn of the lateral meniscus may be connected to the medial femoral condylar region by one or two meniscofemoral ligaments. These structures pass near the posterior cruciate ligament.

The anterior meniscofemoral ligament, when present, passes anterior to the PCL and is commonly called the ligament of Humphrey.

The posterior meniscofemoral ligament passes posterior to the PCL and is commonly called the ligament of Wrisberg.

The presence, size, and arrangement of these ligaments vary between individuals. They contribute to stabilization of the posterior horn of the lateral meniscus and may influence its movement during knee motion.

Relationship to the Medial Collateral Ligament

The medial meniscus is closely associated with the deep medial collateral ligament. The meniscofemoral component connects the medial meniscus toward the femoral side, while the meniscotibial component connects it toward the tibia.

This close relationship helps stabilize the medial meniscus but also limits its mobility. The superficial MCL lies more externally and should be distinguished from the deep capsulomeniscal fibers.

The anatomical connection between the medial meniscus and deep medial collateral complex also explains why substantial medial knee trauma can involve both structures.

Relationship to the Lateral Collateral Ligament

The lateral meniscus has no direct attachment to the lateral collateral ligament. The LCL extends from the lateral femoral epicondyle to the fibular head as a discrete extracapsular ligament.

The popliteus tendon passes deep to the LCL and between the lateral meniscus and surrounding posterolateral capsular structures. This separation is an important anatomical distinction between the medial and lateral sides of the knee.

Relationship to the Popliteus

The popliteus tendon has an important relationship with the lateral meniscus. It passes through the posterolateral region of the joint and is separated from the lateral meniscus by specialized fascial connections.

The interruption in capsular attachment associated with the tendon forms the popliteal hiatus. Fascicles between the popliteus tendon and lateral meniscus contribute to coordinated movement of the lateral meniscus during knee motion.

The popliteus can help draw the lateral meniscus posteriorly during flexion, reducing the likelihood that it will become trapped between the moving femoral and tibial surfaces.

Relationship to the Semimembranosus

The semimembranosus tendon and its expansions are closely related to the posteromedial capsule and medial meniscus. Contraction of semimembranosus can contribute to posterior movement of the medial meniscus during knee flexion through capsular connections.

This dynamic relationship helps accommodate changes in femorotibial contact as the knee moves.

Movement of the Menisci

The menisci are not fixed structures. They move across the tibial plateau as the femoral condyles roll and glide during flexion and extension.

During knee flexion, both menisci generally move posteriorly. During extension, they move anteriorly. The lateral meniscus usually undergoes greater displacement because it is less firmly attached.

Rotational movements of the tibia and femur also alter meniscal position. The exact movement of each region depends on knee angle, loading, ligament tension, and muscular activity.

Knee Movement	General Meniscal Response
Flexion	Menisci move posteriorly
Extension	Menisci move anteriorly
Rotation	Menisci shift in response to changing femorotibial contact

Functions

Increasing Joint Congruity

The femoral condyles are curved, while the tibial articular surfaces are comparatively shallow. The wedge-shaped menisci deepen the functional articular surfaces of the tibia and improve femorotibial congruity.

The concave superior surfaces partially accommodate the femoral condyles, while the flatter inferior surfaces conform more closely to the tibial plateau.

Load Distribution

The menisci distribute compressive loads over a broader area of the tibial plateau. Without normal meniscal function, loads become concentrated over smaller regions of articular cartilage.

The collagen architecture is crucial to this function. Compression tends to push the meniscus radially outward, while circumferential fibers resist this displacement by developing hoop tension.

Shock Absorption

The fibrocartilaginous menisci deform under loading and contribute to shock absorption within the knee. Their ability to distribute forces reduces localized stress on the articular surfaces.

This function operates together with articular cartilage, subchondral bone, synovial fluid, muscles, and other structures involved in transmitting loads through the lower limb.

Joint Stability

The menisci contribute to knee stability by improving congruity between the femur and tibia. Their stabilizing role becomes particularly relevant when other ligamentous restraints are compromised.

The posterior horns provide important secondary restraint in certain directions of tibial translation, although the menisci do not replace the primary stabilizing functions of the cruciate and collateral ligaments.

Joint Lubrication

Movement and deformation of the menisci contribute to the distribution of synovial fluid across the articular surfaces. This supports lubrication and the maintenance of the low-friction environment required for normal knee movement.

Proprioception

Neural elements are present particularly within the peripheral portions and attachment regions of the menisci. These structures may contribute sensory information related to joint position, movement, and loading.

Vascular Supply

The vascular supply of the menisci is concentrated in their peripheral regions. Branches from the genicular arterial network form a perimeniscal vascular plexus that supplies the outer portion of each meniscus.

The inner portion is largely avascular and depends substantially on diffusion from synovial fluid for nutrition. Vascularity is greater in younger individuals and becomes relatively restricted toward the periphery with maturation.

This regional difference in blood supply has major implications for the healing potential of meniscal injuries.

Vascular Zones

Clinically, the meniscus is often divided into zones according to vascularity:

Zone	Location	Vascularity
Red-red zone	Peripheral meniscus	Relatively well vascularized
Red-white zone	Intermediate region	Transitional vascularity
White-white zone	Inner free margin	Largely avascular

These terms are useful clinically but represent a gradual biological transition rather than sharply separated anatomical compartments.

Innervation

The peripheral meniscus, capsular attachments, and horn regions receive sensory innervation from articular branches associated with nerves supplying the knee.

Mechanoreceptors and free nerve endings are concentrated particularly near the vascular peripheral portions and meniscal roots. The inner fibrocartilaginous region has much less neural tissue.

This distribution parallels the general pattern of vascularity, with the peripheral portion being biologically more active than the central free margin.

Biomechanics of Hoop Stress

When the femoral condyle compresses a meniscus against the tibial plateau, the wedge-shaped tissue tends to be displaced outward. The circumferential collagen fibers resist this displacement and convert part of the compressive load into circumferential tensile stress.

The meniscal roots are essential to this mechanism because they anchor the ends of the circumferential fiber system. If a root becomes detached, the meniscus may extrude outward rather than maintaining normal hoop tension.

Radial tears can also interrupt circumferential fibers. A sufficiently extensive radial disruption may therefore substantially impair load transmission even though much of the meniscal tissue remains present.

Differences in Mobility

The lateral meniscus generally moves more freely than the medial meniscus. Its greater mobility reflects its more circular configuration, absence of direct attachment to the LCL, and specialized relationship with the popliteus tendon.

The medial meniscus is more firmly tethered by capsular and deep MCL attachments. Consequently, it has less ability to move away from forces acting between the medial femoral condyle and tibial plateau.

This difference contributes to the distinct injury patterns of the medial and lateral menisci.

Anatomical Variations

The menisci show variation in size, width, thickness, horn attachments, and accessory ligamentous connections. The meniscofemoral ligaments may be present individually, together, or may be poorly developed.

The transverse ligament may also vary substantially or be absent.

A particularly important variation is the discoid lateral meniscus, in which the lateral meniscus is broader and more disc-like than usual. The degree of coverage of the lateral tibial plateau and the stability of peripheral attachments can vary.

Clinical Significance

Meniscal Tears

The menisci may be injured when compression is combined with rotation or shear across the knee. Tears can occur in different orientations depending on the forces involved and the structural condition of the tissue.

Commonly described patterns include longitudinal, radial, horizontal, flap, complex, and root tears. The anatomical significance of a tear depends not only on its shape but also on its location and whether it disrupts circumferential load transmission.

Bucket-Handle Tear

A bucket-handle tear is a displaced longitudinal tear in which an inner fragment can move toward the intercondylar region. The remaining peripheral meniscal tissue resembles the outer portion of a bucket, while the displaced fragment resembles its handle.

Because the displaced fragment may occupy the central joint, this tear pattern can mechanically interfere with normal knee movement.

Radial Tear

A radial tear extends from the free inner margin toward the peripheral meniscus and crosses the circumferential collagen fibers.

Large radial tears are mechanically important because they interrupt the fiber arrangement responsible for hoop stress transmission. The functional consequence therefore depends strongly on the depth and location of the tear.

Meniscal Root Tear

A meniscal root tear affects the attachment of an anterior or posterior horn to the tibia or occurs close enough to the attachment to impair root function.

Loss of effective root fixation allows abnormal meniscal displacement and reduces the ability of the meniscus to convert compressive loads into circumferential tension.

Posterior root pathology is particularly important because of the substantial loads transmitted through the posterior meniscal regions during weight bearing and knee flexion.

Meniscal Extrusion

Meniscal extrusion refers to displacement of the meniscus beyond the peripheral margin of the tibial plateau. It can occur when meniscal structure, root fixation, or surrounding attachments are compromised.

Extrusion reduces the degree to which the meniscus remains interposed between the femur and tibia and can therefore impair normal load distribution.

Discoid Lateral Meniscus

A discoid lateral meniscus is a developmental morphological variation in which the lateral meniscus covers a greater portion of the lateral tibial plateau than usual.

The morphology ranges from relatively broad meniscal tissue to a nearly complete disc. Peripheral attachment stability can also vary. The anatomical variation itself should be distinguished from tears or instability that may occur within the discoid tissue.

Meniscal Cysts

Parameniscal cysts may develop adjacent to a meniscus and are often associated with a communicating meniscal tear. Fluid can extend through the tear into the surrounding soft tissues.

The location of a cyst can therefore provide information about the underlying meniscal region involved.

Healing Potential

The ability of a meniscal tear to heal is influenced by its location relative to the vascular supply. Injuries near the vascular peripheral margin generally have greater biological healing potential than tears confined to the avascular inner region.

Healing also depends on tear configuration, tissue quality, stability, associated injuries, and mechanical environment. Vascular-zone terminology therefore provides anatomical context but does not by itself determine the outcome of an individual injury.

Meniscectomy and Load Distribution

Removal of meniscal tissue decreases the contact area available for transmitting loads between the femur and tibia. The remaining articular surfaces may therefore experience increased contact stresses.

This relationship demonstrates why preservation of functional meniscal tissue is biomechanically important. The menisci are active load-distributing structures rather than expendable remnants within the knee.

Imaging

MRI is particularly useful for demonstrating meniscal morphology, horn and root attachments, relationships with ligaments, and abnormalities within the fibrocartilage.

Normal menisci typically appear as low-signal structures with triangular profiles on appropriate sagittal and coronal images. Interpretation requires knowledge of normal variants and neighboring ligaments because structures such as the meniscofemoral ligaments and popliteus tendon can create appearances that must be distinguished from pathology.

Arthroscopic Anatomy

During knee arthroscopy, the menisci can be examined directly along their articular surfaces and free margins. The anterior horns, bodies, posterior horns, and accessible root regions can be assessed in relation to the femoral condyles and tibial plateau.

The peripheral attachments, popliteal hiatus, cruciate ligaments, and articular cartilage provide important landmarks for understanding meniscal position and integrity.

The medial and lateral menisci are therefore highly organized fibrocartilaginous structures that adapt the geometry of the femoral condyles to the tibial plateau while participating in load distribution, shock absorption, lubrication, and stability. Their wedge-shaped form, circumferential collagen architecture, and firm root attachments are fundamental to these functions.

The differences between the two menisci are equally important. The medial meniscus is more firmly connected to the medial capsuloligamentous structures and is relatively less mobile, while the lateral meniscus has greater mobility and a specialized relationship with the popliteus tendon. These anatomical differences provide the basis for understanding normal knee mechanics and the characteristic patterns of meniscal injury.