Entheses: tendon and ligament attachment sites.

The current brief review focuses on certain issues relating to form-function relationships that are evident at tendon or ligament attachment sites (entheses). It evaluates the development of entheses (both fibrocartilaginous and fibrous) and highlights again an issue largely ignored for decades - i.e. how entheses attached to the metaphyses of long bones manage to keep the same relative position as the bones grow in length. Attention is drawn to the manner in which enthesis fibrocartilage prevents direct cell-cell communication between osteocytes and tendon/ligament cells and how (in a healthy enthesis) it presents a physical barrier separating the blood supply of bone from that of tendon/ligament. The possibility that the thoracolumbar fascia, with its multitude of muscular associations and numerous sites of ligamentous attachment could increase stress concentration at entheses is raised, the structure and development of enthesophytes (bony spurs) is reviewed as is the concept of a synovio-entheseal complex (SEC). How these functional anatomical units (SECs) could trigger pain and inflammation in athletes is briefly discussed.