LAMENESS

Better Target Treatment

DDFT Lesions in the Pastern Frequently Associated with Distal Pathology

By Marie Rosenthal, MS

A horse with a deep digital flexor tendon (DDFT) lesion of the pastern is likely to have concurrent DDFT lesions in other areas of the foot that warrant further assessment for concurrent tendinopathy,” explained Elizabeth V. Acutt, BSc, BVSc, a resident in equine diagnostic imaging at Colorado State University College of Veterinary Medicine.

Identifying these lesions allows the veterinarian to target treatment, which may improve the horse’s outcome, she explained at the 67th Annual Convention and Tradeshow of the American Association of Equine Practitioners, held in Nashville, Tenn.

“We know that deep digital flexor tendon injury is common in equine athletes, and it occurs in a large proportion of horses that present to us for diagnostic imaging of the distal limb,” Dr. Acutt said. In addition, the injuries can occur at several points throughout the length of the tendon.

To get an idea of how many horses with DDFT pastern injuries had concurrent tendinopathy and to determine whether different pastern lesion types would be more likely to be concurrent with other lesions, Dr. Acutt and her colleagues at Colorado State performed a medical record search and identified cases of DDFT tearing in the pastern.

They reviewed 34 high-field MRI scans of 33 horses and 64 ultrasonography examinations of 58 horses.

Ten limbs of 10 horses underwent both ultrasonography and MRI. All the MRIs had been performed under general anesthesia. DDFT lesions in the pastern were classified based upon their configuration as core lesions, dorsal border defects, parasagittal splits or diffuse tendonosis. The goal was to identify the horses with various configurations of pastern DDFT lesions that had additional tendon injury in the foot.

Ultrasound images from a horse with a core lesion in one of the lobes of the DDFT in the pastern (A) and a dorsal border tear of the same lobein the suprasesamoidean region (B) (all lesions indicated by arrows)

Images courtesy of Elizabeth V. Acutt, BSc, BVSc

“It's important to note that all of the lesions that we saw on MRI were also identified and characterized appropriately on our ultrasound,” she said.

“We found that over 90% of the MRI cases that had deep digital flexor tendinopathy in the pastern also had lesions within the foot, and of the 31 limbs that had more distal tendinopathy, pastern lesions were classified as core lesions in the majority of those cases,” Dr. Acutt said.

All horses with core lesions also had foot lesions. There were none with a core lesion that did not have more distal tendinopathy. All of the horses that had insertional lesions also had lesions at that suprasesamoidean region of the tendon, which can typically be visualized on ultrasound.

MR images from a horse with core lesions in both lobes of the DDFT in the pastern (A), parasagittal splits in both lobes in thesuprasesamoidean region (B) and single lesion at the tendon's insertion(C) (all lesions indicated by arrows)

Images courtesy of Elizabeth V. Acutt, BSc, BVSc

Ultrasonography Results

Almost 70% of the ultrasound cases with DDFT lesions in the pastern also had lesions in the foot, and of the 20 limbs in which tendinopathy was confined to the pastern alone, most had defects at the dorsal border of the tendon. Only 1 horse had a core lesion without a foot lesion.

“When we combined our ultrasound and MRI data, it indicated that three-quarters of horses with pastern deep digital flexor tendinopathy also have coexisting distal tendinopathy.” The consistent correlation between core and foot lesions was statistically significant, she added.

“There is a significant association between lesion type and the presence of foot lesions with dorsal border lesions, more frequently confined to the pastern; and the core lesions, more frequently having additional distal tendinopathy,” Dr. Acutt explained. In fact, a horse with a core DDFT lesion in the pastern was almost 20 times more likely to have a concurrent foot lesions than those with other pastern lesion types.

These results lead to another question, she said. Which injury came first, or do they occur simultaneously? In their experience, more horses that have foot lesions without pastern injury than have pastern injury without a foot lesion, according to Dr. Acutt.

“This may suggest that injury begins in the foot and then propagates proximally, but we don't have longitudinal studies to confirm this,” she said. When they looked at repeat scans they did not observe extension in either direction of DDFT injury. In other words, the lesions were static in this population.

Characterizing all the lesions that a horse has would enable veterinarians to direct treatment better, she said, because veterinarians would be able to recommend specific treatment, for instance, if a dorsal border tear occurs at the level of the navicular bursa, bursoscopic debridement might be considered.

In addition, knowing exactly what is going on enables a veterinarian to better predict the horse’s recovery and return to work.

“Different lesion locations have been associated with different prognoses within the literature,” she said. For instance, “horses with tears in the navicular region have been shown to have a higher likelihood of returning to work and remaining sound than horses with suprasesamoidean injuries.

“And there's also been multiple studies that show that horses with multifocal tendinopathy, in general, tend to have worse outcomes than those in which the tear is confined to a single region.”

For more information:

Acutt EV, Contino EK, Frisbie DD, et al. Deep digital flexor tendon lesions in the pastern are associated with the presence of distal tendinopathy. Equine Vet J. 2021 May 20. doi: 10.1111/evj.13470 https://beva.onlinelibrary.wiley.com/doi/epdf/10.1111/evj.13470