Alternative Diagnostic Technique of Equine Laminitis Utilizing Eccentricity of the P3 Bone in the Dorso-Ventral Radiograph

Field: Veterinary (Health Sciences)

The horse hoof has evolved from the same appendage that now makes up the human middle finger, to bear up to 100% of a 500-kg animal, while taking up an area of less than only .05 m2. To meet these exceptionally high mechanical demands, the most distal bone (P3) is suspended in the hoof capsule through a remarkable adaptation of lamina tissue (in humans, this is the tissue underneath a fingernail). The P3 bone is encapsulated by the keratinous hoof (fingernail) in direct contact with the ground and the external environment. The lamina tissue is built to hold the bone so that the P3 bone "floats" within the hoof, providing cushion and impact dampening. When the lamina tissue begins to fail due to sickness, obesity, or age, the developed condition is referred to as laminitis, which causes the P3 bone to rotate downwards. The clinical impact of laminitis is pain, damage to the laminar tissue, and possible humane euthanasia. To diagnose laminitis, veterinarians currently take three radiographs of the horse hoof: from the lateral, ventral, and caudal views. The angle of the bone from the hoof wall in the lateral view is commonly used to diagnosis laminitis. In a healthy animal, this angle would be close to 0 and, in a horse with laminitis, this angle would be much larger. Typically, the other two views are mainly used to determine the overall health of the P3 bone, rather than to help diagnose laminitis. This limits the diagnostic ability of the veterinarian in the case of incomplete, missing, or inconclusive lateral radiographs. The goal of this study therefore was to develop an alternative method of diagnosing laminitis utilizing the ventral radiograph. It was hypothesized that the downward rotation of the P3 bone (as seen in the lateral view) would affect the shape of the P3 bone in the ventral radiograph. More specifically, if the change in the shape of the P3 bone in the ventral radiograph could be measured using the eccentricity of the bone, the ratio of the areas of the P3 bone to hoof, or the difference between the hoof and bone. These measurements were examined to determine if there was statistically significant difference between the healthy and pathological radiographs. The overall goal was divided into two aims: 1) determine if analysis of ventral view images could detect differences in known laminitis and healthy images, and 2) validate the new procedure. In the first aim, 15 sets of radiographs were studied from known cases, of which 7 subjects were diagnosed with laminitis and 8 were confirmed healthy. The angle of the bone from the hoof wall, the areas of the bone and hoof, and eccentricity of the bone were calculated for each case using custom written Matlab programs. It was determined, through statistical testing such as F-tests and 2-way ANOVAs, that eccentricity was the most viable diagnosing method among the three new methods being tested. To validate this diagnostic technique and satisfy the second aim, 35 blinded sets of radiographs were measured and diagnosed with the commonly used method and this new eccentricity-based method. These diagnoses were then compared to a veterinarian's official diagnoses. It was shown, through statistical testing, that eccentricity is an accurate diagnosing technique that exceeds the conventional practice in sensitivity, specificity, false positive rates, and false negative rates.