One of the most frequently occurring developmental disorders in the canine elbow joint is the fractured medial coronoid process of the ulna (FCP). The pathogenesis of this fracture is still largely unknown, but osteochondrotic lesions were found at the predilection site (Grondalen and Grondalen, 1981) and (Wolschrijn, 2004). The presence and contents of cartilage canals and the formation of OC has been reported to be correlated (Kincaid and Lidvall, 1982). In this study it is investigated if the medial coronoid process of the ulna (MCP) in a dog breed predisposed to develop fractured coronoid process (FCP) contains cartilage canals, and if so, to describe their location and their relation to the predilection site in time.

The right elbows of nine young Golden retrievers, aged 4 to 24 weeks, were dissected. The MCPs were fixed in formalin and without prior decalcification embedded in methylmethacrylate. The entire MCP was serially sectioned in the vertical plane from cranial to caudal, and the sections (5μm) were routinely stained.

The apex of the MCP was fully cartilaginous at the youngest ages, with a clear division in a superficial and a deep layer hyaline cartilage. Towards the ulna columnation, cell hypertrophy and spicules were present. After ten weeks of age the enchondral ossification was already present at the apex. It could be substantiated that the medial coronoid process did not develop from a separate ossification centre. From the age of four weeks on three cartilage canals were visible, a medial, a central and a lateral canal, all originating from the periost surrounding the distal parts of the MCP and coursing in a proximal direction. They contained an arteriole, venules, capillaries and loose connective tissue and were surrounded by elongated cells. At 13 weeks two cartilage canals with a smaller diameter were present, and from 16 weeks on no cartilage canals were found.

This pattern has, to our knowledge, not been reported before. The predilection site of FCP is the lateral side of the MCP. This leaves open the possibility that FCP is caused by early chondrification of the lateral cartilage canal, causing insufficient nutrition of the cartilage, leading to osteochondrosis.

REFERENCES

1.  Grondalen J, Grondalen T. 1981. Arthrosis in the elbow joint of young rapidly growing dogs. V. A pathoanatomical investigation. Nord Vet Med 33:1-16.

2.  Kincaid SA, Lidvall ER. 1982. Communicating cartilage canals of the physis of the distal part of the ulna of growing swine and their potential role in healing of metaphyseal dysplasis of osteochondrosis. Am J Vet Res 43:938-944

3.  Wolschrijn CF, Gruijs E, Weijs WA 2004. Micro CT and histology of FCP in a 20 week old dog. Vet Rec accepted