In the ankle, the tibia (shin bone), fibula (calf bone) and talus (ankle bone) meet. It is a weight-bearing joint that allows the foot to extend and flex (plantar and dorsi flexion). The surface where one bone meets the other is covered by a spongy material called cartilage. It acts as a shock absorber and it is lubricated by joint fluid that ensures low friction in the joint.
Pain in the ankle joint is a common condition that can affect people of all ages but predominantly those between 20-40 years of age. This pain can be caused by a sudden ankle injury (e.g. ankle sprain or fracture) or an underlying condition such as arthritis. The condition of the articular talus cartilage itself and that of the underlying bone are highly intertwined, and, when assessing a painful ankle joint, there are many reasons to focus on the entire cartilage and bone unit, instead of just focusing on the cartilage surface alone.
Cartilage has no pain fibers and therefore it cannot be the source of any pain. The bone beneath the cartilage, on the other hand, is richly innervated with pain fibers. Accumulation of fluid in the bone marrow resulting in increased pressure is a common explanation of the pain.