Health Up­date

Re­search of­fers new in­sights for SDFT in­jury prog­no­sis.

Practical Horseman - - Contents -

When a horse injures his su­per­fi­cial dig­i­tal flexor ten­don, know­ing the prog­no­sis for re­cov­ery can help de­ter­mine which treat­ment steps to take. While there are gen­eral stan­dards for es­ti­mat­ing long-term out­come, a new study has de­ter­mined a more sci­en­tific method for pre­dict­ing a horse’s chance of suc­cess­fully re­turn­ing to a per­for­mance ca­reer.

A re­search team focused on ul­tra­sound im­ages of Thor­ough­bred race­horses with SDFT in­juries at ini­tial pre­sen­ta­tion. “These in­juries oc­cur at high-in­ten­sity gal­lop work,” says lead re­searcher Rafael Al­zola, BVMS, MSc, GPCert, Cert AVP, MRCVS, equine surgery res­i­dent at Eng­land’s Not­ting­ham Vet­eri­nary School and Oakham Vet­eri­nary Hospi­tal. He was joined by col­leagues from the Univer­sity of Not­ting­ham, biotech com­pany Ox­tex Ltd. and the head vet­eri­nar­ian at the Hong Kong Jockey Club.

“You could prob­a­bly get nearly all the [in­jured] horses back to rac­ing and through one race,” adds Dr. Al­zola. “But it is whether or not they have a successful ca­reer fol­low­ing the in­jury.”

The re­searchers be­gan by ex­am­in­ing ul­tra­sound im­ages at ini­tial pre­sen­ta­tion taken at the Hong Kong Jockey Club between 2003 and 2014. The study in­cluded 469 horses with only SDFT in­juries in front limbs. “The fan­tas­tic op­por­tu­nity here was that all the horses are kept, trained and raced on the same track and looked af­ter by the same vet group,” says Dr. Al­zola. This elim­i­nated many vari­ables (such as track sur­face) that could have af­fected out­come.

All the in­juries were graded us­ing an es­tab­lished ul­tra­sound scor­ing sys­tem. Then, the re­searchers used a sta­tis­ti­cal model to com­pare the in­juries at ini­tial pre­sen­ta­tion with the horses’ rac­ing ca­reers fol­low­ing in­jury. (This post-re­cov­ery fol­low-up stage is a pri­mary rea­son the study has been on­go­ing for seven years.) The model iden­ti­fied which ul­tra­sono­graphic fea­tures of the SDFT in­jury at ini­tial pre­sen-

tation were good pre­dic­tors of the horses’ abil­ity to suc­cess­fully re­turn to rac­ing (de­fined as com­plet­ing five or more races).

The team looked at horses ex­hibit­ing core-le­sion in­juries, where the ten­don fibers snap, leav­ing what looks like a black hole in the ul­tra­sound im­age. In this type of in­jury, the cross-sec­tional area was the best pre­dic­tive fac­tor. This area is what you see when the im­age is taken with the ul­tra­sound scan­ner per­pen­dic­u­lar to the leg. It’s measured in the SDFT zone show­ing the most dam­age.

When the size of the core le­sion was less than half that of the cross-sec­tional area, the horse had a roughly 29 to 35 per­cent chance of suc­cess­fully rac­ing again. If the le­sion was larger, those odds de­creased to around 11 to 16 per­cent.

For horses without core le­sions—ex­hibit­ing strain and in­flam­ma­tion of the ten­don fibers—re­searchers de­ter­mined that the lon­gi­tu­di­nal fiber pat­tern was the best pre­dic­tive fac­tor. This pat­tern is what shows up when the ul­tra­sound scan­ner is held par­al­lel to the leg. It shows dis­rup­tion in the align­ment of the ten­don fibers and again was measured in the zone with the most dam­age.

In horses where the lon­gi­tu­di­nal fiber pat­tern rep­re­sented less than 75 per­cent of the to­tal SDFT fibers, they had any­where from a 49 to 99 per­cent chance of suc­cess­fully rac­ing again. But when the af­fected area was larger, the prob­a­bil­ity dropped to just 14 per­cent.

“The re­ally im­por­tant mes­sage from our per­spec­tive is that if a horse has an in­jury which is likely to re­cur or fail when they race again, their wel­fare will be bet­ter if this is rec­og­nized [early] and plans are made for an al­ter­na­tive ca­reer or re­tire­ment,” says Dr. Al­zola. “We don’t want to write them off, but we want an in­formed, ev­i­dence-based de­ci­sion on what is best for them in the long term.”

The team be­lieves this study will set the stage for fu­ture work that can help pro­vide more sci­ence-based prog­noses for in­jured horses in other dis­ci­plines. — Sushil Du­lai Wen­holz

Re­searchers study­ing ul­tra­sounds of race­horses with su­per­fi­cial dig­i­tal flexor ten­don in­juries are cre­at­ing a sci­en­tific method to de­ter­mine a horse’s chance of a full re­cov­ery.

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