The perichondrium is the cartilaginous membrane of tight connective tissue that surrounds, stabilizes, and nourishes all hyaline and elastic cartilage except articular cartilage. The perichondrium contains the blood supply to the cartilage tissue associated with it. Injuries to the perichondrium can lead to cartilage damage because the supply to the cartilage is so disrupted.
What is the perichondrium?
Cartilage tissue or cartilage consists of specialized chondrocytes and corresponds to the extracellular ground substance of built-up connective tissue. Cartilage tissue, in the form of articular cartilage, covers the individual joint surfaces of real joints or diarthroses of humans, such as the knee joint or the hip joint. The function of cartilage in joints is to provide low-friction mobility. In addition to joint functions, cartilage is the basic substance of intervertebral discs and menisci. Cartilage tissues of the human body carry a covering layer outside joints, the so-called perichondrium. The perichondrium forms the most superficial layer of cartilage tissue and itself has two layers. Its individual layers correspond to the stratum fibrosum and the stratum cellulare. The enveloping layer not only keeps the cartilage alive, but also supports the regeneration of cartilage damage during growth. Except for the articular surfaces, all hyaline and elastic cartilage in the body bears a perichondrium. Fibrocartilage, on the other hand, lacks perichondrium.
Anatomy and structure
The perichondrium corresponds to a tight layer of connective tissue and thus specialized chondrocytes. The enveloping layer is firmly connected to the cartilaginous tissue via collagen fibers. The structure of the perichondrium consists of two different layers. The stratum fibrosum forms the outer fibrous layer and consists of tight connective tissue with collagen fibers. Thanks to this layer, the joined cartilage has high dimensional stability. The stratum cellulare corresponds to the inner layer of the perichondrium. It is a cell-rich chondrogenic layer containing fibroblasts and mesenchymal cells of the undifferentiated form. The undifferentiated mesenchymal cells may become chondroblasts, or develop into chondrocytes. Thus, they are involved in the appositional growth of cartilage. The perichondrium also contains a capillary network to supply all cartilage tissue. Since the enveloping layer of cartilage accordingly contains many vessels and is also supplied with nerve endings, the enveloping layer is extremely sensitive to pain.
Function and tasks
The perichondrium performs several functions in the human body. All of its functions relate to the cartilage tissue that covers the enveloping layer. First, the perichondrium has a stabilizing effect and counteracts all tensile forces acting on the cartilage through its collagen fibers and elastic fibers. In addition, the perichondrium is responsible for the nutrition and oxygen supply of the cartilage tissue. The tissue fulfills this supply function by means of the vascular apparatus it carries inside it. In addition to nutrients, blood contains oxygen in hemoglobin-bound and free form. In the human body, blood is the most important transport medium. In addition to nutrients and O2, growth factors and messenger substances are partly transported in the blood and reach their target tissues via the bloodstream. In the case of the perichondrium, the transport of oxygen and nutrients from the blood to the cartilage cells takes the form of diffusion within the ground substance. Diffusion is based on an undirected random movement of molecules due to thermal energy. In the case of non-uniform concentration, more molecules move from the areas of high concentration into those of lower concentration. In this way, mass transport occurs without the expenditure of energy and thus represents a form of passive mass transport. From the perichondrium, nutrients and oxygen thus move along the concentration gradient into the cartilage and supply the tissue. The fact that articular cartilage does not depend on a perichondrium is mainly due to the so-called synovial fluid in its joint capsule. This synovial fluid provides the supply that in cartilages with a perichondrium is provided by the enveloping layer. In addition to the above-mentioned functions, the perichondrium can form regenerative cartilage if required in early childhood.In an adult organism, this function is present only to a very small to almost no extent.
Diseases
An extremely painful disease of the perichondrium is called perichondritis. This disease is a bacterial inflammation of the cartilaginous membrane that usually affects the auricle and can spread from there to the internal or external auditory canal. In most cases, the pathogens causing the infection are staphylococci or pseudomonas. The pathogens penetrate the cartilaginous skin via the smallest injuries to the skin, where they multiply. An insect bite is often sufficient as a port of entry. Typically, in perichondritis, the affected tissue swells severely and becomes red. Dermal blistering of the skin may occur, accompanied by severe pain. If left untreated, perichondritis leads to tissue death. Ear injuries can also cause permanent damage to the perichondrium located there. The same applies to injuries to all other perichondrial sheathed cartilage, such as in the area of the intervertebral discs. Injuries to the perichondrium should not be underestimated because the enveloping layer nourishes the cartilage itself. For this reason, after cartilage injuries, perichondrial injuries or even hematomas between the perichondrium and the cartilage, there is always a risk of necroses forming in the cartilage tissue. Such necroses are not fully reversible. In addition, because of the numerous nerve endings in the perichondrial tissue, severe pain is present in the event of any injury to the perichondrium. This pain phenomenon should not be confused with osteoarthritis, which corresponds to a wear and tear of articular cartilage without perichondrium.