The enthesis (plural entheses) is the

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

between

tendon A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its abilit ...

ligament A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal ...

and

bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, an ...

. There are two types of entheses: ''Fibrous entheses'' and ''fibrocartilaginous entheses''. In a fibrous enthesis, the collagenous tendon or ligament directly attaches to the bone. In a

fibrocartilaginous Fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its inflexibility and toughness to the former of these constituents, and its elasticity to the latter. It is the only type of ...

enthesis, the interface presents a gradient that crosses four transition zones: # Tendinous area displaying longitudinally oriented fibroblasts and a parallel arrangement of collagen fibres # Fibrocartilaginous region of variable thickness where the structure of the cells changes to

chondrocyte Chondrocytes (, from Greek χόνδρος, ''chondros'' = cartilage + κύτος, ''kytos'' = cell) are the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteo ...

s # Abrupt transition from cartilaginous to calcified fibrocartilage—often called 'tidemark' or 'blue line' # Bone

Clinical significance

A disease of the entheses is known as an ''

enthesopathy An enthesopathy refers to a disorder involving the attachment of a tendon or ligament to a bone. This site of attachment is known as the enthesis (pl. entheses). If the condition is known to be inflammatory, it can more precisely be called an e ...

'' or ''

enthesitis Enthesitis is inflammation of the entheses, the sites where tendons or ligaments insert into the bone. It is an enthesopathy, a pathologic condition of the entheses. Early clinical manifestations are an aching sensation akin to "working out to ...

''. Enthetic degeneration is characteristic of

spondyloarthropathy Spondyloarthropathy or spondyloarthrosis refers to any joint disease of the vertebral column. As such, it is a class or category of diseases rather than a single, specific entity. It differs from spondylopathy, which is a disease of the verteb ...

and other pathologies. The enthesis is the primary site of disease in

ankylosing spondylitis Ankylosing spondylitis (AS) is a type of arthritis characterized by long-term inflammation of the joints of the spine typically where the spine joins the pelvis. Occasionally areas affected may include other joints such as the shoulders or hip ...

Society and culture

Bioarchaeology

Entheses are widely recorded in the field of

bioarchaeology The term bioarchaeology has been attributed to British archaeologist Grahame Clark who, in 1972, defined it as the study of animal and human bones from archaeological sites. Redefined in 1977 by Jane Buikstra, bioarchaeology in the United States n ...

where the presence of anomalies at these sites, called entheseal changes, has been used to infer repetitive loading to study the division of labour in past populations. Several different recording methods have been proposed to record the variety of changes seen at these sites. However, research has shown that, whichever recording method is used, entheseal changes occur more frequently in older individuals. Research demonstrates that diseases, such as

and

calcific tendinitis Calcific tendinitis is a common condition where calcium deposits form in a tendon, sometimes causing pain at the affected site. Deposits can occur in several places in the body, but are by far most common in the rotator cuff of the shoulder. Aro ...

, also have to be taken into consideration. Experimental studies have demonstrated how loading history (physical activity) can increase the relative size of muscle attachment sites.

History

"Enthesis" is rooted in the Ancient Greek word, "ἔνθεσις" or "énthesis," meaning “putting in," or "insertion." This refers to the role of the enthesis as the site of attachment of bones with tendons or ligaments. Relatedly, in muscle terminology, the insertion is the site of attachment at the end with predominant movement or action (opposite of the origin). Thus the words (''enthesis'' and ''insertion''

f muscle F, or f, is the sixth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''ef'' (pronounced ), and the plural is ''efs''. His ...

are proximal in the

semantic field In linguistics, a semantic field is a lexical set of words grouped semantically (by meaning) that refers to a specific subject.Howard Jackson, Etienne Zé Amvela, ''Words, Meaning, and Vocabulary'', Continuum, 2000, p14. The term is also used in ...

, but ''insertion'' in reference to muscle can refer to any relevant aspect of the site (i.e., the attachment per se, the bone, the tendon, or the entire area), whereas ''enthesis'' refers to the attachment per se and to ligamentous attachments as well as tendinous ones.

References

External links

Enthesis information site
at www.enthesis.info
Image of enthesis
at

Medscape Medscape is a website providing access to medical information for clinicians; the organization also provides continuing education for physicians and health professionals. It references medical journal articles, Continuing Medical Education (CM ...

Enthesopathy and Soft Tissue Shadows
at chiroweb.com