[Duplication of the acromioclavicular joint: A case dating from the end of the 19th century].

The duplication of the acromioclavicular joint is a very rare anomaly of shoulder girdle. Here, we present a new case of unilateral duplication of the acromioclavicular joint observed on an individual from the 19th century. In the literature, two hypotheses are proposed to explain the origin of this anomaly. The first is a congenital origin that could be explained by in utero displacement of one of the clavicle's primary ossification centers, or the existence of an additional ossification center. The second is a traumatic origin resulting from an acromioclavicular fracture that occurred during the growth period of the individual. Our macroscopic observations and CT-scan images show no sign of a healed fracture, of complications, or of a bone callus after healing. The hypothesis of a congenital origin for this acromioclavicular duplication is therefore preferred.