Answer:
The cause of bone fusion in joints damaged by rheumatoid arthritis is due to the over activity of the synovium.
Step-by-step explanation:
Synovium -
Synovium is a lining that covers the joints of the body , which is responsible for lubrication of the joints and to move easily .
The disorder rheumatoid arthritis is caused by the over activity of this lining , as it swells out and becomes inflamed , and hence, can destroy the joint and even the ligament and the tissues .
The weakening of these ligament can lead to deformities like claw toe or hammer toe.