Luzanne van der Laan, Robert M. Kirberger, Geoffrey T. Fosgate, Christelle Le Roux

Background

Medial coronoid process disease (MCPD) is the most common cause of canine elbow dysplasia, leading to lameness in young large-breed dogs. Computed tomography (CT) is the preferred imaging modality to assess the medial coronoid process (MCP) due to its superior spatial resolution and absence of bone overlap. However, limited information exists regarding the normal MCP shape and density in clinically healthy dogs. This study aimed to describe the CT appearance and Hounsfield unit (HU) variability of the normal MCP, medial radial head (MRH), and lateral radial head (LRH) in young adult Labrador Retrievers, establishing reference data for future diagnostic comparisons.

Methods

This retrospective descriptive study analyzed CT scans from 51 purpose-bred, clinically sound South African guide dogs (Labrador Retrievers, aged 12–13 months). Only dogs confirmed free of elbow dysplasia (ED) on both radiography and CT were included. Bilateral elbows were imaged under sedation using a Siemens Emotion Duo scanner (1 mm slice thickness, 130 kVp, 70 mAs, bone algorithm). Multiplanar reconstructions were aligned at three consistent levels of the MCP (−1 mm, 0 mm, +1 mm from the apex). Two reviewers independently classified MCP shapes and measured HU for the MCP, MRH, and LRH. Intra- and interobserver repeatability, as well as sex-based differences, were statistically evaluated.

Results

Three principal MCP shapes were identified—ovoid, triangular, and softly pointed—which corresponded consistently to the −1, 0, and +1 mm imaging levels, respectively. There were no significant shape differences between sexes or sides, with excellent interobserver agreement (κ = 0.97).
Mean MCP HU values ranged from 1501–1526 HU in females and 1460–1490 HU in males, with significantly higher density in females (p < 0.001). The MRH consistently demonstrated higher HU than the LRH at all levels, reflecting greater medial joint load. Mean MRH HU ranged from 1183–1245 HU (females) and 1148–1219 HU (males); LRH HU ranged from 785–832 HU (females) and 705–759 HU (males). MCP density was highest at level −1 and lowest at +1. Intra-observer repeatability was good (ICC = 0.90 at level −1), while interobserver repeatability was moderate. Volume averaging occurred most frequently at +1 mm.

Limitations

The retrospective design and absence of arthroscopic or histopathologic confirmation limited diagnostic certainty of “normal” joints. The study focused exclusively on 1-year-old Labrador Retrievers, precluding age or breed comparisons. HU values may vary between scanners, and small measurement errors during image alignment could influence results. Additionally, mild volume averaging at certain levels reduced measurement precision.

Conclusions

This study establishes reference standards for normal MCP morphology and bone density in young adult Labrador Retrievers. The MCP displays predictable shape variation with CT slice level, and both sex and anatomical location influence HU values. The MCP HU is most reliably assessed at level −1, while MRH HU is best evaluated at level 0. These findings provide a robust baseline for identifying pathological deviations in early elbow dysplasia and for standardizing CT assessment techniques in future veterinary orthopedic research.

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