RINGBONE

EQUUS - - Conformation Insights -

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

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