There are two different types of entheses. Fibrous entheses are characterised by pure dense fibrous connective tissue that links the tendon or ligament to the bone, but fibrocartilaginous entheses have a transitional zone of fibrocartilage at the bony interface. Most entheses are fibrocartilaginous—for example, those of the annulus fibrosus, Achilles tendon, and most insertions on long bone epiphyses or apophyses. Typically, four zones of tissue are present—dense fibrous connective tissue, uncalcified fibrocartilage, calcified fibrocartilage, and bone. The two fibrocartilage zones are separated by a calcification front known as the tidemark.

 Uncalcified fibrocartilage probably reduces stress concentration by gradually dissipating any fibre bending and stretch-induced narrowing of the tendon/ligament away from the junctional region where wear and tear are most likely to occur. It is prominent at sites at which a great deal of bending of the tendon/ligament accompanies joint movement. It also creates a vascular and cellular barrier between bone and tendon/ligament cells.

 The calcified fibrocartilage serves to link the tendon/ligament to the bone via an irregular interface—probably in the manner of a jigsaw, with little direct continuity of collagen fibres. The stress dissipation role of enthesis fibrocartilage hinges on its compression tolerance properties—any bending or narrowing of a tendon/ligament increases compressive loading. As in articular cartilage, its ability to resist compression is linked to the presence of aggrecan and type II collagen in the extracellular matrix. These molecules have been demonstrated at several entheses by rerverse transcriptase-polymerase chain reaction, western blotting, and/or immunohistochemistry. At most sites, they are synthesised by fibrocartilage cells that appear relatively late in development by fibroblast metaplasia. In the inner annulus, however, the fibrocartilage is derived from hyaline cartilage that is present during early development.