Fractures of Ossified Rib Cartilages in the Horse – a Concern of Veterinarians?

In connection with an osteological study of more than one hundred complete, disarticulated skeletons of the Norwegian Fjord and Døle horse breeds in the collection of the University Museum of Bergen, attention was drawn to the ossified parts of the rib cartilages because of frequent healed fractures transverse to the cartilages. Unossified cartilage had been removed, so the ossified cartilages were available as dry specimens. The skeletons derive from pedigreed stallions as well as some few mares, so both name, year of birth and age are known. Most often the age was between 15 and 30 years, but some few horses were younger, the youngest 5‐year‐old. Ocular inspection of each skeleton revealed that healed fractures occurred in ossified rib cartilages of every horse, varying from some few instances to >30. Skeletons of horses of other races in the museum collection corroborated this. Healing of the fractures was obvious. Four kinds were observed: The first, and probably least sincere fracture appeared as a visible transverse ring, the second displayed callus elevation around the fracture, the third showed dislocation and callus formation, and the fourth concerns pseudoarthrosis, when fractured parts fail to unite during healing. Even a fifth kind may be considered, with circumferential callus formation leaving the interior healed but unfused. X‐ray displays the fractures as white, cross‐sectional bands of bone repair. However, such fractures appear not to be considered in contemporary veterinary pathology, but the large number of fractures observed in some cases, callus formation and dislocation of fractures in others, indicates that some period following these fractures is likely to have been traumatic to the horse, so that fracture of ossified rib cartilages should not be ruled out concerning horses showing unexplained symptoms of pain.