The coronary band is dynamic, Taylor said, and asymmetric weight bearing can influence its shape. She described a healthy coronary band (as viewed from the side) as nearly straight or with a slight upward arch. Often, horses develop one-sided coronary band asymmetry in the heel that is referred to as sheared heels. Horses with sheared heels frequently experience displacement of one hoof quarter along with the heel bulb, and they commonly develop painful conditions such as quarter cracks or thrush.
Veterinarians can use the angle the coronary band forms with the ground to estimate the position of the coffin bone within the hoof capsule. A normal coronary band angle is considered to be about 20° to 25°, Taylor said; if the coronary band angle is greater than 30°, the horse probably has an extremely low or negative palmar/plantar angle (the angle bottom of the coffin bone make with the ground; hooves with an angle of greater than 45° undoubtedly have a negative palmar/plantar angle, she added). Simply put, negative palmar/plantar angles mean the horse’s heel is being crushed.
“At the other extreme, a coronary band parallel to the ground as viewed from the side is indicative for a high palmar angle,” she said, noting this is often seen in laminitic horses or those with a club foot.
The coronary band angle could also indicate other problems within the hoof capsule. Taylor explained that the coronary band angle correlates with the normal forces the coffin joint encounters and the force the deep digital flexor tendon exerts on the navicular bone. For instance, she said, as the coronary band angle increases, the palmar/plantar angle decreases, and both the torque on the coffin joint and the force on the navicular bone increase. These biomechanical forces could initiate or aggravate heel pain, deep digital flexor tendon strain, and/or coffin joint disease.
Additionally, Taylor said, in a healthy hoof, the hair along the coronary band should lie flat on the hoof wall; consider hair pointing in an outward direction an abnormality because it could indicate excessive ground reaction forces on the hoof wall.