Foreign body synovitis is a painful reaction to an object that gets embedded into the body.  Although this usually happens in the hand, it may occur in any part of the body.  The foreign body can be any object such as a thorn, splinter, glass etc.  The foreign body causes an inflammatory reaction in and around the area which is painful.  Both joints and tendons may be affected by this problem.  The inflammatory reaction may cause pain and limitation of function of the extremity.  Diagnosis of foreign body synovitis is made by history.  In the absence of a history of trauma to the area, X-rays, MRI and ultrasound of the area may be useful in detecting the embedded object.  Blood work is useful to identify the presence of infection and exclude other causes of pain such as auto-immune disease, arthritis and gout.  Treatment is mainly removal of the offending object with surgery, followed by treatment of infection and pain with oral or intravenous medications.