A large amount of bridging new bone is present on the dorsal, plantar and lateral aspects of tibia and especially at the tibio-tarsal joint. The surface of the new bone formation is smoot and the opacity heterogeneous. The bone opacity of the talus is reduced.

• Bony mass around tarsus with ankyloses of tibiotarsal- and intertarsal joints
• Severe osteopenia talus

The list of differential diagnoses includes multiple cartilaginous exostoses and changes associated with diffuse, idiopathic hyperostosis (DISH). The bilateral symmetrical nature of the changes would be unusual for a traumatic cause. The radiological findings are not compatible with enthesiophytosis or degenerative joint disease.

Due to Wolff’s law, a lack of bone loading results in bone loss; thus the osteopenia of the talus is the result of disuse due to ankylosis. Due to the traction of the Achilles tendon, which causes some loading and thus stimulation of bone turnover, the calcaneus is affected to a lesser degree. Assessment of the degree of osteopenia of the central tarsal and 1^st row of tarsal bones is impossible due to superimpositioning. A small degree of osteopenia affecting the distal tarsal bones could be present and could be explained by a small degree of retained movement in the tarso-metatarsal joints.

Due to the absence of vertebral abnormalities such as ossification of the ventral longitudinal ligament, as would be expected in DISH, it is likely that “Tyson” is suffering from a form of multiple cartilaginous exostoses.