Magnetic resonance imaging of entheses. Part 1.

Entheses are the sites of attachment of a tendon, ligament, or joint capsule to bone. Many features of entheses are adapted to disperse stress and accommodate compressive and shear forces at, or near, boundaries between tendons or ligaments and bone. Of particular interest is calcified and uncalcified fibrocartilage, which has mechanical properties that differ from those of tensile regions of tendons or ligaments, and from bone. Ultrashort echo time (UTE) pulse sequences can identify the specific tissue components of entheses and differentiate cortical bone, calcified fibrocartilage, uncalcified fibrocartilage, and fibrous connective tissue. Magic angle imaging can also differentiate tissues, such as fibrocartilage and tendon, which have different fibre orientations. Understanding the magnetic resonance (MR) appearance of entheses involves consideration of tissue properties, fibre-to-field angle, magic angle effects, pulse sequences, and geometrical factors including fibre-to-section orientation and partial volume effects. New approaches using MR imaging, allow entheses to be visualised with much greater detail than previously possible, and this may help in biomechanical studies, diagnosis of disease including overuse syndromes and spondyloarthropathies, as well as monitoring tissue repair and healing.