An enthesis (pl. entheses), also known as a footprint, generally refers to the anatomic junction where connective tissue (e.g. ligaments, tendons, joint capsules) attach to bone.
Enthesis are commonly classified into two types 1:
In a fibrous enthesis, the collagen fibers comprising ligament or tendon attach directly to periosteum or bone cortex 1,2. They are usually associated with short tendons, e.g. gluteus maximus insertion onto the femur 1. This usually occurs along a relatively wide area of a bone shaft 1.
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 1.
- 1. Anthony S. Tadros, Brady K. Huang, Mini N. Pathria. Muscle-Tendon-Enthesis Unit. (2018) Seminars in Musculoskeletal Radiology. 22 (03): 263. doi:10.1055/s-0038-1641570 - Pubmed
- 2. D'Agostino MA, Terslev L. Imaging Evaluation of the Entheses: Ultrasonography, MRI, and Scoring of Evaluation. (2016) Rheumatic diseases clinics of North America. 42 (4): 679-693. doi:10.1016/j.rdc.2016.07.012 - Pubmed