Why does it occur?
The pathology i.e. the abnormality is swelling of the lining of the joint or tendon sheath with further thickening due to multiplication of the local cells. They in turn produce inflammatory fluid leading to further swelling which may be diffuse or discrete such as a ganglion (see information sheet). Often there is an obvious initiating cause such as an injury but many patients develop symptoms for no obvious cause, probably due to the wear and tear of life.
The response of the synovial cells is designed to deal with the underlying problem such as injury or infection. Often this works and the hand settles after a period of pain stiffness and swelling. Sometimes the synovitis persists and can perpetuate itself by causing damage to the local tissues by the chemicals produced in the inflammatory fluid. A steady state may be reached of chronic pain, swelling and discomfort which may or may not be tolerable to the patient. Otherwise there will be increasing symptoms and the patient will seek medical help.
Joint synovitis: essentially this is a form of joint arthritis i.e. joint inflammation and is treated in the same way (see information sheets). It does however imply a milder state that often resolves well if treated early.
Tenosynovitis: this usually presents like a mild form of trigger finger/thumb (for which it is probably a precursor and can be treated in the same way (see information sheets). Sometime it can be very dramatic.