Investigation into the morphology of the third metacarpal bone in the horse

Abstract

AIMS: To describe key morphological attributes of the third metacarpal bone (Mc3) of horses and to determine whether or not the symmetry of the Mc3 varied significantly between limbs of the same horse.

METHODS: Ten pairs of metacarpi were collected from slaughter facilities. The age and breed of the horses were recorded. Fixed points and axes that could be easily reproduced between bones were identified on high-quality photographic images of each bone. Using image analysis, three angles were measured. Angle gamma measured the rotation around the long axis of the diaphysis of Mc3, angle delta the angle between the dorsal long axis of the cannon bone and the surface of the condyle of Mc3, and angle theta the angle between the surface of the condyle and the long axis of the sagittal ridge of the condyle of Mc3. These angles represent some of the characteristic morphologic relationships within the equine Mc3.

RESULTS: The coefficient of variation for angles gamma, delta and theta and were 1.2%, 0.2% and 0.5%, respectively. Angle gamma was larger in the left compared with the right limb (p=0.041). Angles delta and theta were larger in the right compared with the left limb (p=0.001 and p=0.003, respectively). There was a single outlier in a left limb for angle gamma. When this was excluded from the analysis, angle gamma in the left limb was still larger than in the right limb. Angle delta was consistently greater than 90° in 19/20 metacarpi.

CONCLUSIONS: There were significant morphological differences in the Mc3 between the left and right limbs of the 10 horses examined. These findings provide some reliable reference data for future investigation. Further work is required to document these differences in a larger population of horses and to determine whether the morphology of the Mc3 is influenced by age or other factors such as use of the animal.

KEY WORDS:

• Horse
• third metacarpal bone
• distal limb conformation
• morphology
• condylar fracture
• laterality
• handedness

Acknowledgements

The authors would like to acknowledge Dr. Chris Rogers for his assistance with the statistical analysis and Dr. Elwyn Firth for his support, guidance and expertise.

Notes

¹ http://www.tandfonline.com/doi/suppl/10.1080/00480169.2011.651056

Additional information

Notes on contributors

DC Dymock

Current Address: University of Florida, College of Veterinary Medicine, Department of Large Animal Clinical Sciences, Gainesville, FL, 32610-0136, USA