Concussion does not cause ringbone; rather, it arises in a way similar to splints, that is, through tension or “jerk” affecting the fibers of ligaments and tendons investing the pastern area. In this body zone, “jerk” most commonly comes from unlevel mediolateral hoof strike, which in turn is due either to unlevel hoof trim, to use on hard, lumpy ground, or else in dry sand into which the edges of the hoofs can suddenly sink. Numerous fibrous tissues that invest the pastern bones can be affected, including the collateral ligaments as well as the branches of the suspensory ligament complex that insert below the ankle joints. The tendinous insertions of the superficial digital flexor and long extensor muscles are frequently also involved.
Rolf’s skeleton shows evidence of
severe ringbone, with obvious exostosis (left, yellow arrows) but no actual fusion of the joints. The exostosis tends, exactly as in splints, to overcoat and thus preserve the fibers it affects. In the macerated specimen, the areas of insertion of ossified tissues appear as rough, raised lines.
In addition, the whole of the anterior and lateral faces of Rolf’s short pastern bones are coated by thick, rough exostosis. The numerous smooth-edged, round holes that are visible in the front view of the short pasterns formed around proliferating blood vessels, which suggests that Rolf’s pasterns would have been hot to the touch, there was a throbbing pulse, and that the stallion would have been quite lame. In a recent telephone interview, Gary Clarke, director emeritus of the Topeka Zoo, confirmed that during the last several years of his life Rolf was put on anti-inflammatory medication to reduce discomfort.
Medication was necessary in any case, as Rolf also suffered from systemic arthritis that affected most of his joints. “Arthrosis”
shows up on the bones of arthritic horses as exostotic “lipping” along the edges of joints (blue arrows). Lipping may limit joint
mobility to a mild or moderate extent; it usually also induces pain upon movement.
Lexington’s pasterns (opposite, top) are much cleaner than Rolf’s, displaying only small ossified ridges marking the insertions of the extensor branches of the suspensory apparatus (yellow arrow A), the insertion of the tendon of the superficial digital flexor muscle (B) and collateral ligaments (C). As in most horses, Lexington’s hind pasterns are clean.
As noted in “Structure of Skeletal Bone: Normal vs. Rotten,” page 46, the outer lamellar “shell” of Ethan Allen’s bones (above) has largely rotted away, exposing the cancellous bone within. This postmortem damage is not pathology, and there is no pathology whatsoever evident on Ethan Allen’s pasterns or coffin bones.
The same may be said for the bones of his sire, Black Hawk (left): They are as clean as a whistle, confirming again that both of these horses were as reported, very sound and siring sound.
Lexington had mild ringbone-type exostosis, left fore and hind. LEFT FORE LATERAL VIEW LEFT HIND MEDIAL VIEW
Rolf’s skeleton shows ringbone on the long and short pasterns of the right side. SIDE VIEW FRONT VIEW
Black Hawk’s right fore and right hind pasterns and coffin bones show no pathology. RIGHT FORE, SEEN FROM THE FRONT RIGHT HIND, OBLIQUE LATERAL VIEW
LONG PASTERN BONE REAR VIEW SIDE VIEW SHORT PASTERN BONE FRONT REAR COFFIN BONE LATERAL VIEW COFFIN BONE, SEEN FROM ABOVE Ethan Allen’s fore pastern bones and coffin bone show no pathology.
Ethan Allen’s hind pastern bones and coffin bone show no pathology. COFFIN BONE, SEEN FROM ABOVE COFFIN BONE LATERAL VIEW LONG PASTERN BONE REAR VIEW SIDE VIEW SHORT PASTERN BONE FRONT REAR