What is an amphiarthrosis? Characteristics and classification

The amphiarthrosis are the joints that have a very limited range of movement, whose bony surfaces are generally flat or concave and their structure is mainly cartilaginous.

Amphiarthrosis differs from the synarthrosis in the structure of bone union through cartilage; that of synarthrosis is composed mainly of non-cartilaginous fibrous tissue.

Synchondrosis of the spine (cartilaginous articular disc).

The amphiarthrosis have an interosseous joint space, which does not become a proper cavity; this space is occupied by fibrocartilage or hyaline cartilage and is surrounded by interosseous ligaments, the latter being responsible for the stability of the joint.

These joints, which for some are called secondary joints, have body stability as their main function. Its structure is designed to be able to withstand shock forces and to be flexible in specific situations.

What is the cartilage?

Cartilage is a type of specialized firm connective tissue, with the consistency of a soft plastic, and formed by chondrocytes and a dense extracellular matrix composed of proteins, water, collagen and proteoglycans.

The chondrocytes, which only represent 5% of the tissue, are responsible for producing the collagen and proteoglycans sufficient to maintain the extracellular matrix, which makes up 95% of the tissue. This fabric fulfills as its main function the reduction of friction in the bony union acting as a lubricant.

Likewise, it has the capacity to withstand high cyclical loads in a unique way, without evidence of degenerative damage, while protecting the bone ends acting as a shock absorber, since it has elastic resistance to pressure due to high mechanical loads.

Cartilage unlike bone, does not need blood supply, innervation or lymphatic drainage for maintenance and proper functioning, receives its nutrition by diffusion through the extracellular matrix.

However, due to this, its regenerative capacity is poor with respect to bone regeneration capacity, representing one of the greatest challenges in orthopedic medicine today.

There are 3 types of cartilage: hyaline cartilage, elastic cartilage and fibrous cartilage. The hyaline cartilage, named for its glassy and translucent appearance, also known as articular cartilage is that which is found mainly in ampiarthrosis, is 2 to 4 mm thick.

Classification of amphiarthrosis

Structurally it is within the group of fibrocartilaginous joints, and according to the type of cartilage tissue can be classified into:

Synchondrosis or primary cartilaginous

Also called true or cartilaginous amphiarthrosis, are those in which the bones are bound by hyaline cartilage and are in direct contact with it.

In turn, the synchondrosis may be temporary, such as those that are part of the ossification nucleus of the growing bones, or they may be permanent, those that after being formed, the adult bone continues to be in contact with hyaline cartilage as in the spinal column. .

Symphysis or secondary cartilaginous

Also called diarthroanfiarthrosis, fibrocartilaginous fusions are very robust between two bony structures, which usually have a pseudocavity inside with a rudimentary synovium.

The symphysis is usually located in the mid sagittal line of the human body and the most representative is the pubic symphysis.

It is also called mandibular symphysis to the small crest in the midline of the jaw, which indicates the site of union of the two hemiarchies, although it is not properly a symphysis, since it lacks fibrocartilaginous tissue.

Functionally, it is within the group of semi-mobile joints, with characteristics that place it between the diarthroses and the synarthrosis. They comply with the mobile function described above.

References

1. Meriam-Webster Medical Dictionary (2017) Retrieved from: merriam-webster.com
2. Encyclopedia Britannica. Cartilage. Anatomy Written by: Encyclopedia Britannica Publishers (2007) Retrieved from: britannica.com
3. US National Library of Medicine National Institutes of Health. The Basic Science of Articular Cartilage. Structure, Composition, and Function. Sports Health. 2009 Nov; 1 (6): 461-468. Alice J. Sophia Fox, MSc, Asheesh Bedi, MD, and Scott A. Rodeo, MD. Retrieved from: ncbi.nlm.nih.gov
4. BioSalud Day Hospital International Clinic of Biological Medicine since 1985. What is Articular Cartilage? Retrieved from: biosalud.org
5. Viladot Voegeli, Antonio. Basic biomechanics lessons of the locomotor system. p. 53. Retrieved from: books.google.es