The subchondral split line patterns of the medial coronoid process in canine ulnae

The subchondral split line patterns of the canine medial coronoid process (MCP) were compared with fragmentation line patterns of the MCP in case of elbow dysplasia. Split line patterns were determined in paired ulnae from the killed 26 large-breed dogs ranging in age between 0.8 and 15 years and in two ulnae affected by fragmentation of the MCP. The macerated ulnae were degreased with methylene chloride and decalcified in 5% nitric acid. The subchondral bony layer was pierced at right angles in regular intervals using a round needle that was dipped in black liquid acrylic colour. Three main types of split line patterns could be differentiated (i.e. a sagittal type, a transverse type and an intermediate type). In the sagittal type, split lines were aligned in parallel to the lateral border and at right angles to the rim of the tip and medial border of the MCP. In the transverse type, split lines were orientated in a transverse line to both collateral borders. The intermediate type was characterized as a transition type between sagittal and transverse type as the split lines were aligned obliquely to the longitudinal axis of the MCP. These three types corresponded well with the fissure and fragmentation line patterns of the MCP. The present findings strongly suggest an association between split line pattern and type of fragmentation of the MCP.