AMPHIARTHROSIS: CHARACTERISTICS AND CLASSIFICATION - MEDICINE - 2024

The amphiarthrosis are joints having a very limited range of motion, whose bone surfaces are generally flat or concave and is primarily cartilaginous structure.

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

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

These joints, which by 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 cartilage?

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

Chondrocytes, which only represent 5% of the tissue, are responsible for producing enough collagen and proteoglycans to maintain the extracellular matrix, which makes up 95% of the tissue. The main function of this tissue is to reduce friction at the bone junction, acting as a lubricant.

Likewise, it has the ability to withstand high cyclic loads in a unique way, without evidence of degenerative damage, while protecting the bone ends by functioning as a shock absorber, as it has elastic resistance to pressure due to high mechanical loads.

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

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

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

Classification of amphiarthrosis

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

Synchondrosis or primary cartilaginous

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

In turn, synchondroses can be temporary, such as those that are part of the ossification nucleus of growing bones, or they can be permanent, those that after having formed, the adult bone continues in contact with hyaline cartilage as in the spine.

Symphysis or secondary cartilaginous

Also called diarthroamphiarthrosis, they are very robust fibrocartilaginous fusions between two bone structures, which normally have a pseudocavity inside with a rudimentary synovium.

The symphyses are usually located in the midsagittal line of the human body and the most representative is the pubic symphysis.

The small ridge in the midline of the mandible is also called the mandibular symphysis, which indicates the site of union of the two hemiarcades, although it is not properly a symphysis, since it lacks fibrocartilaginous tissue.

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

References

1. Meriam-Webster Medical Dictionary (2017) Recovered from: merriam-webster.com
2. Encyclopedia Britannica. Cartilage. Anatomy. Written by: Encyclopaedia Britannica Editors (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. Recovered from: ncbi.nlm.nih.gov
4. BioSalud Day Hospital International Clinic of Biological Medicine since 1985. What is Articular Cartilage? Recovered from: biosalud.org
5. Viladot Voegeli, Antonio. Basic biomechanics lessons of the locomotor system. p. 53. Recovered from: books.google.es