Enthesis

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An enthesis (plural: entheses), also known as a footprint, generally refers to the anatomic junction where connective tissue (e.g. ligament, tendon, joint capsule, bursa or a combination thereof) attach to bone.

Enthesis are commonly classified into two types :

  • fibrous
  • fibrocartilage

Histology

Fibrous

In a fibrous enthesis, the collagen fibers comprising ligament or tendon attach directly to periosteum or bone cortex . They are usually associated with short tendons, e.g. gluteus maximus insertion onto the femur . This usually occurs along a relatively wide area of a bone shaft .

Fibrocartilage

A fibrocartilage enthesis represent a more complex attachment between tendon and bone. They generally occur at locations where tendon inserts onto a portion of bone lacking periosteum, e.g. an epiphysis.

They are classically divided into four zones:

  • collagen zone - derived from tendon or other soft tissue structure
  • non-calcified fibrocartilaginous zone - variable thickness where chondrocytes predominate
  • calcified fibrocartilaginous zone - an abrupt transition ("tidemark or blue line)
  • subchondral bone zone

    • The zonal organization is thought to result in decreased stress on the interface .

    Related pathology

    • enthesopathy: a pathological condition affecting the enthesis
    • enthesitis: an inflammatory condition causing enthesopathy
    • enthesophyte: bony projection at an enthesis in response to enthesopathy