[Ossification in chronic Achilles tendinosis: a third calf bone]

Ossification of the Achilles tendon is a rare complication of chronic Achilles tendinosis. This case report discusses a 59-year-old man who experienced Achilles tendon lengthening in early childhood due to a congenital clubfoot disorder with a record-breaking ossification of a length of 10 cm. Because of persistent symptoms and the risk of fracture, the choice of treatment after unsuccessful conservative therapy depends on surgical reconstructive criteria.