<prompt> A most common cause of bony ankylosis-Rheumatoid arthritisPyogenic arthritisTraumatic arthritisOsteoarthritis  <response>: AnkylosisAnkylosis is the fusion of bones in a joint leading to stiffness of the joint.Ankylosis may be : -1 Fibrous ankylosis: - Two articular surfaces are fused by fibrous tissue.The feature are : -Some movement of joint is possible though just a jog of movement.Movements may be painless or painful.Most common cause is tubercular arthritis.2 Bony ankylosis: - There is a bony union between two articular surfaces. The features are : -No movements possible.a Joint is painlessA most common cause is acute suppurative arthritis septic arthritis.Sometimes, stiffness may also occur due to extra-articular etiology such as in Bum contracture, myositis ossificans etc. It is called False ankylosis. 