The Palmar Metric: a novel radiographic assessment of the distal phalanx in the horse Monique F.
1 Craig ,
John J.
1 Craig ,
and Matthew A.
2 Burd
Visual Explanation of Method
Introduction Our method computes a measure of the concavity of the palmar aspect of the pedal bone from a standard-practice lateral radiograph. Our palmar metric quantifies the ‘flatness’ or ‘cuppiness’ of the pedal bone. We propose it as a useful tool in any study that seeks to understand what factors lead to demineralization of the pedal bone throughout the horse’s life. As an example, we show that pedal bones tend to flatten throughout any horse’s lifetime. We ask: what hoof-care practices would minimize the rate of loss of the palmar concavity?
University-Industry Collaboration
The ‘Palmar Curve’
Methods
Quantification
Three independent groups of horses were used as the basis of this study. In total, 821 digital LM radiographs were analyzed. Group #1 is a mixed breed group of 266 front feet, group #2 is a mixed breed group of 277 front feet, and group #3 consists of 278 Quarter Horse front feet. A new measure was developed, the “palmarmetric” which is based on measuring the area under a profile we call the ‘palmar curve’ which is evident in high quality LM radiographs of the equine digit. This is a calculated ratio, expressed as a percentage, of the area under the coffin bone relative to the area of a certain rectangle described by the bone. Its value is dependent on the shape of the solar surface of the coffin bone. The more curve to the bone (solar concavity) the greater the ratio. Formulating this measure as a ratio of areas means that no scaling system is required for the radiograph, and also that our metric is not dependent on foot size. The value of the palmar metric ranges from zero (a totally flat pedal bone) up to values as high as 15.0 or more. Our algorithm for computing the palmar metric from a standard-practice LM radiograph has been implemented and is available in the commercially available Metron-DVM software. The Palmar Metric was negatively correlated with age and decreased at a rate of 0.28 % per year for horses of various breeds (group #1 and group #2) and 0.33 % per year for Quarter Horses (Group #3). Analysis of precision errors (0.05-0.71) and CV (0.67-14.1 %) indicated there was a range of proficiency demonstrated by the individual users. The overall precision error and CV indicated one can expect up to a 14% difference in the Palmar Metric dependent on user expertise. Radiographic positioning, if orientation was correct to within 10 degrees, did not significantly impact precision.
References
Contact me! Monique@EponaTech.com www.Epona-Institute.org
The mark-up and measurement process of our method is now a part of the Metron-DVM software found in DR and CR systems used around the world by veterinarians.
Applied to actual horse
Results In our group #1 and #2 study of 543 feet of known age, the palmar-metric was calculated. The graph includes the linear regression line, y= -0.28x + 9.98, r2=0.28, P<0.05, and shows the interesting result that the palmar-metric, on average, decreases with age. The wide scatter of the data indicates that many factors other than age must also affect the palmar metric. One could determine if a given individual lies above or below the value of the trend line for it’s age as a means of rating the horse as having a below or above average P3 bone. In a second study, we plot our metric for group #1 versus the palmar-angle. Again, a wide scatter is apparent, but the data suggests a weak optimum of around 3.75 degrees, suggesting that palmar angles higher or lower than this value lead to increased demineralization of the pedal bone.
Academic institutions that have equine science programs teach subjective evaluation of horse conformation. Although quantitative methods have been reported, only recently have tools for rapid objective quantification been developed. Due to advances in imaging technology, conformation of the horse, including foot conformation, can now be assessed accurately and quantitatively. Using undergraduate students as examiners, we have investigated several ways of quantifying the morphometrics of the equine hoof and lower leg, such as the project reported here. The Cal Poly Animal Science department has teamed with the Epona Institute in a fruitful universityindustry collaboration which gets undergraduates involved with research projects. 1. The Epona Institute
543 Front Hooves
2. Cal Poly San Luis Obispo, Animal Science Dept.
* Parks AH. Form and function of the equine digit. Vet Clin Equine 2003;19:285–307. * Craig J, M Craig, T Weltner. Quantifying conformation of the equine digit from lateromedial radiographs. In: Proceedings Assoc Equine Sports Med 2001; 21:20-25. * Rocha JV, CJ Lischer, M Kummer, M Hässig, JA Auer. Evaluating the measuring software package Metron-PX for morphometric description of equine hoof radiographs. Journal of Equine Veterinary Science 2004;24:347-354.