Enthesis

Enthesis (plural: entheses) is the point at which a tendon or ligament^[1] or muscle^[2] inserts into bone, where the collagen fibers are mineralized and integrated into bone tissue. The collagen to bone interface is via Sharpey's fibers.

Classification

There are two types:

• Fibrous entheses
• Fibrocartilaginous entheses

In a fibrous enthesis, the collagenous tendon or ligament directly attaches to the bone, whilst the fibrocartilaginous enthesis displays 4 zones during the transition from tendon/ligament to bone:

• i) tendinous area displaying longitudinally oriented fibroblasts and a parallel arrangement of collagen fibres
• ii) a fibrocartilaginous region of variable thickness where the structure of the cells changes to chondrocytes
• iii) an abrupt transition from cartilaginous to calcified fibrocartilage - the so-called 'tidemark' or 'blue line'
• iv) bone

Pathology

A disease of the entheses is known as an "enthesopathy" or "enthesitis" and is characteristic of spondyloarthropathy but is present in other pathologies as well.

The enthesis is the primary site of ankylosing spondylitis.

References

External links

• Image of enthesis at Medscape
• Enthesopathy and Soft Tissue Shadows at chiroweb.com
• Resnick D, Niwayama G (1983). "Entheses and enthesopathy. Anatomical, pathological, and radiological correlation". Radiology 146 (1): 1–9. PMID 6849029. http://radiology.rsnajnls.org/cgi/content/abstract/146/1/1. 
• Origin of phrase at rheuma21st.com at rheuma21st.com