Fibrocartilage: Definition, Function, Position, Symphysis Pubis, Meniscus and Tissue Identity

It is the only type of cartilage that contains type I collagen in addition to normal type II.

White fibrocartilage consists of a mixture of white fibrous tissue and cartilage tissue in various proportions. It owes its flexibility and toughness to the first of these components, and its elasticity to the last.

During labor, relaxin relaxes the pubic symphysis to facilitate delivery, but this can lead to posterior joint problems.

Fibrocartilage is found in the pubic symphysis, the fibrous annulus of the intervertebral discs, the menisci, the triangular fibrocartilage, and the temporomandibular joints.

It is also present at the tendon bone interface, where there is a transition from the soft tendon to the calcified and non-calcified fibrocartilage before becoming bone.

pubic symphysis

It is a cartilaginous joint that is located between the upper and left branches of the pubic bones. It is located in front of and below the urinary bladder.

In men, the suspensory ligament of the penis attaches to the symphysis pubis. In women, the pubic symphysis is intimately close to the clitoris. In normal adults, it can move about 2 mm and with 1 degree of rotation. This increases for women at the time of delivery.

The name comes from the Greek word “symphysis”, which means “to grow together.”

Disco intervertebral

An intervertebral disc (or intervertebral fibrocartilage) is located between the adjacent vertebrae in the spine.

Each disc forms a fibrocartilaginous joint (a symphysis), to allow slight movement of the vertebrae , and acts as a ligament to hold the vertebrae together. Their role as shock absorbers in the spine is crucial.

Intervertebral discs consist of an external fibrous annulus, the annulus fibrosus disci intervertebralis, which surrounds an internal gel-like center, the nucleus pulposus. The annulus fibrosus consists of several layers (sheets) of fibrocartilage composed of type I and type II collagen.

Type I is concentrated towards the edge of the ring, where it provides greater resistance. Rigid sheets can resist compressive forces. The fibrous intervertebral disc contains the nucleus pulposus and this helps distribute pressure evenly across the disc.

This prevents the development of stress concentrations that could cause damage to the underlying vertebrae or to their end plates. The nucleus pulposus contains loose fibers suspended in a mucoprotein gel.

The disc nucleus acts as a shock absorber, absorbing the shock of the body’s activities and keeping the two vertebrae apart. It is the remnant of the notochord.

There is a disc between each pair of vertebrae, except for the first cervical segment, the atlas. The atlas is a ring around the approximately cone-shaped extension of the shaft (second cervical segment).

The shaft acts as a pole around which the atlas can rotate, allowing the neck to rotate. There are 23 discs in the human spine: 6 in the neck (cervical region), 12 in the middle of the back (thoracic region), and 5 in the lower back (lumbar region).

For example, the disc between the fifth and sixth cervical vertebrae is called “C5-6.”

Meniscus (anatomy)

A meniscus is a fibrocartilaginous, crescent-shaped anatomical structure that, unlike an articular disc, only partially divides a joint cavity.

In humans, they are present in the knee, wrist, acromioclavicular, sternoclavicular, and temporomandibular joints; in other animals they may be present in other joints.

Generally, the term “meniscus” is used to refer to the cartilage of the knee, either the lateral or medial meniscus. Both are cartilaginous tissues that provide structural integrity to the knee when subjected to tension and torsion.

The menisci are also known as “semi-lunar” cartilages, referring to their crescent shape. The term meniscus is from the ancient Greek μηνίσκος (meniskos), which means ‘increasing’.

Triangular fibrocartilage

The triangular fibrocartilage complex suspends the ends of the radius and ulna bones above the wrist. It is triangular in shape and is made up of various ligaments and cartilage.

The triangular fibrocartilage complex allows the wrist to move in six different directions: bending, straightening, twisting both ways and side to side.

There is a small pad of cartilage called the articular disc in the center of the complex that cushions this part of the wrist joint.

Temporomandibular joint

They are the two joints that connect the jaw with the skull. It is a bilateral synovial joint between the temporal bone of the upper part of the skull and the lower jaw, from which it derives its name.

Tendon-bone interface

The tendon-bone interface (enthesis) is a highly sophisticated biomaterial junction that allows the transfer of stresses between mechanically different materials.

Enthesis encounters very high mechanical demands and regenerative capacity is very low, resulting in high rates of rupture recurrence after surgery.

Tissue engineering offers the potential to restore the functional integrity of entheses. However, recent enthesis tissue engineering approaches have been limited by a lack of knowledge about the cells present at this interface.

Fibrocartilage identity

Fibrocartilage has been reported in mammals, birds, reptiles, amphibians, and fish. In its clearest form, it can be easily recognized by both routine histology and immunohistochemistry.

Histologically, a ‘typical’ fibrocartilage is an avascular and aneural tissue that has large, round or oval cells embedded in an embedded capacitance material (ECM) in which collagen and elastic fibers are readily visible, as in ordinary dense fibrous connective tissue.

However, in addition, there is a small amount of amorphous, pericellular and territorial matrix that is metachromatically stained with toluidine blue. It is the ability to distinguish fibers in routine histology slides that is critical in distinguishing fibrocartilage from hyaline cartilage.

In hyaline cartilage, the fibers are normally not visible in routine sections, as the rest of the matrix masks the fiber. Immunohistochemically, fibrocartilage is typically characterized by the presence of type II collagen and aggrecan, as in hyaline cartilage.

The absence of any of the molecules in the body as a whole can have severe effects on spfacelogenesis.

The practical difficulty in trying to define fibrocartilage accurately is that there are no clear limits that allow histological and immunohistochemical features to form the basis for an empirical definition.

Thus, type II collagen and aggrecan, for example, can be expressed in many non-cartilaginous tissues, eg, muscle or tissues in the developing ear.

Nor can fibrocartilage be more easily defined on the basis of its biochemical composition.

Eyre et al . have pointed out that the menisci of the knee joint (which are one of the best-known fibrocartilages) contain only a small amount of type II collagen, in what is largely a matrix rich in type I collagen, but that the discs Human IVs contain roughly equal amounts of both.

Therefore, it must be accepted that fibrocartilage cannot always be unequivocally distinguished from dense fibrous connective tissue on the one hand or hyaline (and occasionally elastic) cartilage on the other.

There is a continuous spectrum of tissues between these two extremes and fibrocartilage always blends imperceptibly with one or the other.

Thus, the typical hyaline articular cartilage covering the head of the humerus, for example, is often fibrocartilaginous near the junction of the rotator cuff tendons and fibrocartilage in menisci, IV discs, tendons, and ligaments mixed with tissue fibrous.

Therefore, fibrocartilage should be considered as a “transitional tissue” and the reader cannot assume that a tissue present in one location, or stage of development, is the same as another.

The idea that fibrocartilage is a transitional tissue is consistent with its developmental origin, as it can differentiate both dense fibrous connective tissue and hyaline cartilage.

This makes it difficult to know what to call your cells. We choose to simply refer to them as fibrocartilage cells, while others call them fibrochondrocytes.

However, the terms fibroblasts or cartilage cells (chondrocytes) can sometimes be applicable, although not interchangeable, according to the origin of tissue development.

Such difficulties in defining cell phenotypes are not, of course, restricted to fibrocartilage, but are often a general problem in skeletal biology.

Fibrocartilage function

Fibrocartilage is a dynamic tissue that develops at sites where entheses are subject to shear and compression forces. It also has the ability to promote bone formation, as shown by histological analysis during postnatal growth.

Gradual (rather than abrupt) flexing of the soft tissues of entheses near the margins of the joint, which is a consequence of the stiffness of the matrix by proteoglycans in the entheses fibrocartilage, dissipates the stress concentration at the site of Union.

However, it also means that parts of the enthesis and adjacent tissues are compressed during joint traction. The idea is best understood in relation to the Achilles tendon and is the archetypal example of the concept of the organ of enthesis.

When the foot is dorsiflexed, the Achilles tendon gradually flexes in the region of the fibrocartilage plug as the angle of insertion at which the tendon approaches the heel is changed.

Consequently, the immediately adjacent part of the tendon is compressed against the superior tuberosity of the calcaneus. The mutual compression of tendon and bone leads to the formation of a sesamoid fibrocartilage on the deep surface of the former and a periosteal fibrocartilage on the surface of the latter.

Basic mechanical engineering principles would suggest that a tendon that bends under load would be more prone to failure. The enthesis itself, the periosteal fibrocartilage, the bursa, and the fat pad collectively comprise the organ of enthesis of Achilles as originally defined.

Together, they all work in one way or another to reduce the concentration of stress on the enthesis itself.

Because the deep crural fascia in the lower leg effectively serves as a retinaculum to reduce bow chord and flexion that would otherwise occur at enthesis, it can also be considered part of the enthesis organ complex.

This concept of an organ of enthesis has wide applicability, and an organ of enthesis is seen in many other places in the body.

Fundamentally, the development of an enthesis organ depends on the presence of a microscopic pulley site immediately adjacent to the enthesis itself or an enthesis that is in a well, that is, the adjacent bone is slightly elevated in comparison.

The rheumatological meaning of the concept of the enthesis organ is that it helps to explain why patients with enthesopathies may present with symptoms that affect the immediately adjacent area rather than just the tendon / ligament / bone junction.

Similar biomechanical conditions that lead to fibrocartilage formation in and near entities exist at other sites, including regions where tendons or ligaments wrap around bony pulleys (for example, where the peroneal tendons wrap around the lateral malleolus in the ankle) and some synovial joints (sacroiliac and sternoclavicular joints).

Entheses are often considered to be well supplied with pain and proprioceptive receptors.

However, studies of rat Achilles tendon enthesis have shown that healthy enthesis is aneural and that nerve fibers are restricted to neighboring tissues, for example the epithenon and particularly the protruding tip of the Kager fat pad. in the retrocalcaneal bag.

Therefore, in its lack of nerve fibers, the fibrocartilage in enthesis parallels the articular cartilage of a synovial joint.

Fibrocartilage is also avascular, and the enthesis blood supply is derived largely from vessels in the peritenon and adjacent bone marrow.

Fibrocartilage position

In fibrocartilage, the matrix is ​​dominated by a dense regular network of bundles of collagen fibers arranged parallel to each other in several layers.

The bundles in the adjacent layers run in different directions (like the layers in a joint capsule), producing a strong material with moderate elasticity. Fibrocartilage is found in various places and forms, in particular:

Joint discs: Complete or incomplete discs interposed between the articular surfaces of some synovial joints, including the knee joint, the sternoclavicular joint, and the acromioclavicular joint.

In these joints, the discs improve congruence (the area over which joint reaction forces are distributed) and joint stability. In addition, the discs deform in response to load and therefore provide shock absorption.

Symphysis Joints : Complete discs that join the bones at the symphysis joints. These joints include the symphysis pubis and the joints between the bodies of the vertebrae.

In these joints, the deformation of the disc in response to load allows movement between the articulating bones and provides shock absorption.

Styling in ball joints : Extension to the concave articular surface in a ball joint (eg, shoulder and hip joints) in the shape of a labrum (lip) around the edge of the articular surface.

A labrum deepens the socket, which increases the joint area and therefore the stability of the joint.

Lining of the bony grooves : The lining of the bony grooves and channels that are occupied by tendons, such as the tibialis posterior tendons, the flexor longus of the fingers, and the flexor longus of the big toe in a groove behind the medial malleolus.

The grooves act as pulleys that normally increase the mechanical efficiency of the associated muscles.