Ankle Synovitis. (Also known as Post-Traumatic Ankle Synovitis). Ankle synovitis is a condition characterized by inflammation of the soft tissue lining the ankle joint capsule, known as the synovium, with subsequent ankle swelling, pain and stiffness.nkle synovitis is a condition characterized by inflammation of the soft tissue lining the ankle joint capsule, known as the synovium, with subsequent ankle swelling, pain and stiffness.