EQUUS CON­SUL­TANTS

EQUUS - - Equus -

Living with a mus­cle ab­nor­mal­ity

Q:My 21-year-old Ara­bian geld­ing, a re­tired en­durance horse, was di­ag­nosed with fi­brotic my­opa­thy a lit­tle over a year ago. One hindquar­ter is more af­fected than the other, and he ex­hibits a mild “slap­ping” gait on that leg un­til he warms up. My vet­eri­nar­ian told me that, although my horse was not in pain, it would be best for him to work only on flat trails.

Can you tell me more about the cause and pro­gres­sion of the dis­ease? There was no trauma in the limb that I’m aware of, and I’m al­ways very care­ful about proper warm­ing up be­fore work. Does the my­opa­thy even­tu­ally sta­bi­lize, or does the mus­cle con­tinue to shorten/ scar over time? If it sta­bi­lizes, can the horse be slowly ex­er­cised on more than flat ground? When I turn him out in the arena he gal­lops around and seems to en­joy it. Does this fur­ther dam­age the mus­cle? Other than the surgery, are there any treat­ments? Elis­a­bet Hiatt Santa Cruz, Cal­i­for­nia

A:Fi­brotic my­opa­thy is a con­di­tion that oc­curs when scar tis­sue de­vel­ops in the big mus­cles on the back of the thigh (think ham­strings in peo­ple). This group of mus­cles pulls the leg back dur­ing the stride and thus is re­spon­si­ble for much of the im­pul­sion a horse gen­er­ates with his rear legs. Scar­ring pre­vents the mus­cles from ex­tend­ing to their full length; the short­ened mus­cles act like a gi­ant rub­ber band, pulling the foot down and back, re­sult­ing in the “slap­ping” gait you de­scribed. Your vet­eri­nar­ian is ab­so­lutely right that this is not a painful lame­ness but sim­ply a lim­i­ta­tion of func­tion.

The scar­ring in the mus­cles usu­ally re­sults from some form of in­jury, pos­si­bly a lac­er­a­tion or a kick. In rare cases, a horse who ha­bit­u­ally leans on the butt chain in a trailer will de­velop fi­brotic my­opa­thy. An­other pos­si­bil­ity is tear­ing of the mus­cle fibers caused by ex­treme ex­er­tion. Be­cause your horse is af­fected in both legs, it is pos­si­ble that he gave ev­ery­thing he had in some of his en­durance rides and dam­aged the mus­cles.

It is un­com­mon for fi­brotic my­opa­thy to progress in sever­ity un­less the horse re­peats the in­jury or con­tin­ues to hurt him­self. Gal­lop­ing in the pas­ture should not be a prob­lem.

Se­vere cases of fi­brotic my­opa­thy may be treated with surgery to cut the semi­tendi­nosus ten­don or mus­cle in an at­tempt to re­lease the lim­it­ing ef­fect of the scar. The pro­ce­dure is not al­ways suc­cess­ful be­cause scar­ring may re­oc­cur at the sur­gi­cal site. Shock­wave treat­ments and pos­si­bly deeper pen­e­trat­ing laser ther­apy can help in some cases. From your de­scrip­tion, it sounds like your horse is only mildly af­fected and likely would not ben­e­fit sub­stan­tially from any treat­ment.

You are for­tu­nate be­cause most horses with fi­brotic my­opa­thy do not warm up out of the lame­ness. Con­tin­u­ing to pay spe­cial at­ten­tion to warm­ing up prop­erly at the start of each ride makes sense for you. Also, be­cause there are lim­i­ta­tions to how far your horse can step with his hind legs, you’ll need to be care­ful in deep or un­even ter­rain. But as long as you re­mem­ber all of this, I sus­pect you can still par­tic­i­pate in quite a few ath­letic en­deav­ors with your horse.

STRENGTH: The big mus­cles at the back of the horse’s thigh are re­spon­si­ble for much of the im­pul­sion he gen­er­ates with his rear legs.

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