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The enthesis is the point where a tendon or ligament attaches to a bone. It is differentiated from the tendon, ligament or bone by the mineralization of the collagen fibers that fuse with the bone itself. This mineralization allows the enthesis to become part of the bone and to anchor the muscle or ligament to the bone.
The plural form of enthesis is entheses. There are two main types of enthesis in the human body. They are either fibrous or fibrocartilaginous. Fibrous entheses attach themselves directly to the bone and are the simpler of the two forms.
Fibrocartiloginous entheses have a four-phase transition from tendon to bone. The first stage happens in the tendinous area where there are parallel fibroblast and collagen fibers. Second is the fibrocartilaginous region, which is identified by its chondrocyte cell structures. The third section is the calcified fibrocartilage, which directly links to the fourth phase, the bone.
The arm is a good example of the function of an enthesis. The triceps and biceps muscles are attached to the arm at both ends by tendons and entheses. The muscle stretches from one bone to another over the elbow joint. The entheses anchor the muscles in place allowing them to perform their function. The entheses usually do not snap, and any muscle recoil is caused by the breaking of the tendon linking the enthesis to the muscle.
Enthesitis, also called enthesopathy, is the inflammation of the enthesis. An inflammation is the swelling of tissue. Symptoms of enthesitis include pain and swelling, usually around the heel, but also around the fingers and toes. If related to psoriatic arthritis, there may be inflammations at other points as well.
The entheses are prone to damage as they are major points of compression and stress in the body. All movement pushes and pulls the enthesis’ attachment to the bone. The nature of any damage done during enthesitis depends on the nature of tissue repairs made to the entheses on a microbiological level.
It is possible to examine and track the damage to the enthesis using ultrasound and magnetic resonance imaging (MRI). Ultrasound provides a better image and is able to better track early signs of problems. This includes the blurring of the tendon boundaries, fat degradation and the formation of intratendinous lesions.
Enthesitis is treated by treating the underlying cause. Such causes include trauma or injury, overloading the enthesis or psoriatic arthritis. Physicians will know best how to treat each problem, whereas treating just the inflammation will only allay the symptoms of the problem and not the problem itself.