A pastern joint prob­lem

EQUUS - - Eq Consultant­s -

Q:Re­cently I saw a horse who was re­cov­er­ing from surgery for an­nu­lar lig­a­ment con­stric­tion on the hind legs. Ap­par­ently, he had been “knuck­ling over” be­cause the an­nu­lar lig­a­ment was con­strict­ing the pastern in the hind legs. I had never heard of this con­di­tion be­fore. Can you tell me more about it? Carolyn Kay Harper Philo­math, Ore­gon

A:To un­der­stand how things can go wrong in the pastern joint, you first need to ap­pre­ci­ate how the ten­dons and lig­a­ments work to­gether when they’re healthy. The pal­mar-plan­tar an­nu­lar lig­a­ments are very tough, fi­brous struc­tures that wrap hor­i­zon­tally around the back of fet­lock joints. In ad­di­tion to sup­port­ing and sta­bi­liz­ing the joints, the an­nu­lar lig­a­ments support the flexor ten­dons, which run down the back of the horse’s legs, and they pro­vide a canal for th­ese ten­dons to glide through as the horse works.

Th­ese struc­tures may be placed un­der huge amounts of strain. Think of the force ap­plied to the rear legs as an even­ter jumps over an ob­sta­cle or on the front legs as he lands.

In­juries and in­flam­ma­tion in the an­nu­lar lig­a­ments or the flexor ten­dons can cause thick­en­ing and stiff­en­ing in ei­ther struc­ture. As a re­sult, the canal be­hind the fet­lock may grow smaller, or the ten­don that slides through it may grow big­ger. Ei­ther way, the abil­ity of the ten­don to glide freely past the fet­lock joint is di­min­ished, and the horse will be un­able to com­pletely ex­tend the fet­lock and set the foot flat on the

ground. In­flam­ma­tion and ad­he­sions of the ten­don to the sheath make this a painful con­di­tion that gets worse when the horse ex­er­cises.

The horse you saw was ap­par­ently af­fected in the rear legs, but this con­di­tion can oc­cur in the front fet­locks, too. The prob­lem may ap­pear in any breed but is of­ten as­so­ci­ated with sport horses, race­horses and warm­bloods.

Treat­ment for an­nu­lar lig­a­ment syn­drome is sim­i­lar to some of the treat­ments for carpal canal (tun­nel) syn­drome in peo­ple: The fet­lock canal is widened sur­gi­cally by cut­ting the an­nu­lar lig­a­ment. This surgery has a very good suc­cess rate (in one study, 87 per­cent of the horses re­turned to ath­letic sound­ness) if the in­jury in­volves only the an­nu­lar lig­a­ment and not the flexor ten­dons. Horses with a flexor ten­don in­jury (bowed ten­don) in that area did not do nearly as well, with only 38 per­cent be­com­ing sound.

Bruce A. Con­nally, DVM, MS

Wy­oming Equine Long­mont, Colorado

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