Coffin Bone Fractures (Ossicles) in Young Horses
by Richard A. Mansmann, VMD,PhD
The radiograph shows fractures in the developing wings of the coffin bone in a 13-month-old TB colt. There is a fragment on both sides of the developing wings of the coffin bone. This colt had similar lesions in the opposite foot at 6 months, which were completely healed by 13 months.
Fractures or ossicles in the developing wings of the coffin bone (third phalanx of P3) appear to be common in young horses. Coffin bone fractures in horses younger than 2 years of age heal more readily than those in horses over 2 years of age. So, whenever these wing fractures or ossicles are found in sucklings, weanlings, or yearlings, they should simply be given time to heal; surgery, confinement, and shoeing changes are usually unnecessary. It is recommended that healing be monitored with a single radiography (x-ray) every 2 months until the lesions have resolved. This common phenomenon in foals may be a traumatic form of developmental bone disease, and could be considered to be a sentinel for nutritional or other pasture footing problems (ground too hard, too many rocks, etc.).
In 1978, I found some irregularly scalloped areas (ossicles) in the developing wings of the coffin bone in three foals I had bred and raised. I was concerned, but the foals all developed normally and their coffin bones were radiographically normal by 15 months of age. Later, I had the opportunity to x-ray the feet of several young horses on a well-managed Thoroughbred and Appaloosa breeding farm. We found 13 healthy (i.e. sound) young horses with these ossicles on their coffin bones. In 1990, we x-rayed 6 foals every two months from 2 to 14 months of age. Four of the six foals had ossicles in at least one foot, all of which had "healed" completely by 14 months of age and caused no apparent problems.
The size and distribution of these ossicles are variable. They may be found in one or both wings of the same coffin bone, and in one or both feet. They are not necessarily symmetrical. They occur more often in the front feet, but may be found in the hind feet. These ossicles or fractures do not involve any part of the coffin joint.
Over the years, I have seen or read about foals that have had surgery to remove these "fracture fragments;" foals that have been discriminated against at sales, and foals that were treated with stall confinement or special shoeing. None of the 20 foals I have studied, and none of at least 20 others with which I have been involved, have had any lameness or developmental problems that were confirmed to be related to their P-3 ossicles. All have "healed" while being maintained in their farm's normal foal environment with no special treatment or management changes. (Note: Even more extensive fractures involving the body of the coffin bone or extending into the coffin joint seem to heal better in horses under 2 years of age than in older horses.)
It is my opinion this "temporary ossicle formation" in the P-3 is a very common phenomenon in young horses. These ossicles are probably not part of the normal development of the equine coffin bone, so they could be a form of traumatic developmental bone disease (i.e. trauma of some type causing a lesion in developing bone). They could also be a sentinel for pasture footing or nutritional problems in a particular herd.
In 1986, Dr. Yovich and others published a series of cases of coffin bone fractures in young horses. Three of the foals, ranging in age from 2 weeks to 5 months, had similar radiographic changes to the one shown above. Of the foals in which later radiographs were taken, the coffin bones developed normally.
Dr. Ric Redden, in an unpublished study, found ossicles in at least one foot in 115 out of 149 foals on six Thoroughbred farms in Kentucky. Some of these foals were lame and some had club-footed conformation, but others were sound.
In 1993, Dr. Kaneps and others from the University of California at Davis suggested that these ossicles are fractures, although lameness histories on the affected foals were unclear. The theory as to how or why these fractures occur in the developing wings of the coffin bone involves three key points:
- The foal's hoof and coffin bone are soft and do not mature until 2-3 years of age.
- The fractures occur at or near the junction between the coffin bone and the cartilage that will ossify with maturity into the wing of the coffin bone. In other words, the fractures occur in an area of developing bones.
- The deep flexor tendon attaches onto the underside of the coffin bone at about this level.
According to the theory, the fractures occur while the foal is running around in the field. During a sharp turn, the ground forces on the developing wing of the coffin bone exert pressure in one direction, while the deep flexor tendon pulls the coffin bone in another direction. The result is a small fragment of bone broken off the margin of the coffin bone, as shown in the radiograph above.