Tuesday, July 16, 2013

Hallmarq Standing MRI Presents: Navicular Disease Diagnosis, Then and Now

We have never really understood navicular disease, but maybe we're getting closer. Two horses would have identical lameness symptoms but the radiographs were clean on one, and clearly showed a bone lesion in the other. Some horses stayed lame for years and were never ridden again. Others took a year or so off and, to everyone’s surprise, returned to training.

Navicular disease confounded veterinarians, frustrated trainers and broke the hearts of riders and owners young and old. But as the sophistication of veterinary medicine improved, so did the accuracy of both the diagnosis and prognosis for horses suffering from what we started to call “navicular-type lameness”.

The farrier profession joined forces with veterinarians to fight the war on navicular disease. Farriers adopted the use of bar shoes, pads, impression material and complex localized combinations of hard and soft materials to support the hoof and take stress off the navicular bone, navicular bursa, deep flexor tendon, and/or the ligaments of the navicular zone. Sometimes it was a trial-and-error process. Coffin joint and navicular bursa injections helped sometimes, too, as might injectable treatments like Legend and Adequan. And then there was shockwave, vibration, acupuncture, chiropractics, changes in bedding and arena footing, joint supplements and an arsenal of medications.

But that was then.

The classic perception of “navicular disease” was that the pain would be caused by a cyst-like lesion within the navicular bone. However, radiographs of sound horses also occasionally showed navicular bone lesions. In the study, 68 of the horses had some type of navicular bone lesion, such as this one detailed in a sample Hallmarq standing MRI, in addition to a tendon injury in the foot.

Since the advent of standing MRI for the horse, veterinarians are able to see the inside of the foot from every angle. They are able not only diagnose the health of the navicular bone, they can evaluate the bursa, the tendon and the ligaments, and look for clues to the horse’s pain.

And when they find the source, they can accurately judge if the problem is likely to respond to treatment.

Eugenio Cillán García, LV, MSc, MRCVS
Lecturer in Equine Surgery
And the picture is improving even more. Last month, a paper was published that separates the types of injuries to the deep digital flexor tendon and plots the prognosis for a return to performance. “Deep digital flexor tendon injury within the hoof capsule; does lesion type or location predict prognosis?”, by authors Cillán-García, Milner, Talbot, Tucker,  Hendey, Boswell, Reardon, and Taylor is a paper with important information not only about the injuries inside the foot that cause navicular-type pain, but how the location and type of injury will affect the likelihood of the horse returning to its previous level of performance.

Cillán-García led researchers at the University of Edinburgh in Scotland, who reviewed 168 horses that had been evaluated for foot lameness that was subsequently diagnosed as being caused by a lesion or tear in the DDFT. All the horses had both front feet scanned with the Hallmarq Standing MRI unit, either at the private Liphook Equine Hospital, University of Liverpool or at the University of Edinburgh.

The authors write: “Lesions of the DDFT were divided into core lesions, dorsal border lesions and parasagittal splits. Lesion location was documented.”

This study is important in many ways. First of all, all horses had the same procedures followed, which meant both radiographs and MRI scans of the foot, as well as a standard lameness exam. Once diagnosed, they were all subject to a standardized program of stall rest followed by gradually increased exercise.

All the horses in the study were shod according to a standard set for them, using a graduated heart-har shoe. (Photo courtesy of Eugenio Cillán García)
Farriers will find it interesting that all the horses were shod according to the same prescription: graduated heart bar shoes with latero-medial rolling to reduce the break-over forces, and thus, the tension on the DDFT. In some cases, modifications of the shoeing, such as silicone pads, open gradu- ated heels, graduated egg bar shoes were used depending on the hoof conformation. A shortened shoeing cycle of four to six weeks was advised for the first three shoeings after diagnosis.

After 18 months had passed, owners were asked how the horses were doing.

The authors collected the owners’ statements and reported, “Of 168 horses with primary DDFT injury, 54 horses had dorsal border lesions, 59 had parasagittal splits and 55 had core lesions. Twenty-five per cent of all horses returned to previous levels of athletic activity within 18 months of MRI evaluation.

All the horses in the study suffered from some form of lesion in the deep digital flexor tendon. The lesions were in many different locations and the severities varied among the study horses. The most significant finding of the study is that horses with dorsal border lesions of the DDFT do better than other kind of lesions. Photo courtesy of Eugenio Cillán García.
Additional pathologies of the navicular zone were reported in 108 (67 per cent) cases, including navicular bone abnormalities. desmitis of the medial or lateral collateral ligament of the distal interphalangeal joint, osteoarthritis of the distal interphalangeal joint, adhesions between the navicular bone and the DDFT, and desmitis of the distal sesamoidean impar ligament. Common non-specific findings included effusions of the distal interphalangeal joint and/or navicular bursa.

Horses with complete splits or core lesions of the DDFT were significantly less likely to return to some level of athletic activity than horses with dorsal border lesions . Dorsal border lesions of the DDFT appear to have a better prognosis than core lesions or parasagittal splits.

Hallmarq infographic compares the route to recover for horses diagnosed with and without MRI to back up the diagnosis.

The authors concluded that injury to the deep digital flexor tendon is still a serious threat to a horse’s athletic future but that by using MRI to pinpoint both the location and severity of the injury it may be possible to give owners an accurate picture of what the horse’s future may hold.

An important fact that emerged from the study was that horses that were referred for MRI within 0–8 weeks of onset of lameness, had a significantly increased likelihood of returning to some level of athletic activity compared with horses referred after a longer period.

Without equine MRI, vets use the limited tools available to them to diagnose the probable cause of lameness, and prescribe treatment on this basis. In effect, they are doing it the old-fashioned way, and without the accuracy afforded by MRI.

The most common approach to lameness is to check the hoofcare, rest the horse and treat conservatively. Improvement in the condition is generally taken as confirmation of the diagnosis, but this process is only effective around 30% of the time. If the horse fails to improve the vet will investigate again in search of a different diagnosis, but often a horse will be investigated many times over before a satisfactory conclusion is reached (if ever).

The outcome of horses treated in this way varies, as the catch-all “navicular syndrome” diagnosis covers many different pathologies. Some of these injuries do originate in the navicular bone, others in structures such as the navicular bursa, coffin joint, tendons or ligaments.

Standing MRI can return clear images of each of these structures. With high quality MRI images, picturing the inside of the foot as "slices" in different planes, vets can make diagnoses with more confidence than ever before.

MRI may seem expensive, but when comparing the costs it is important to weigh up the alternative potential costs of multiple trial-and-error shoe-rest-treat cycles, and the other costs incurred through remedial farriery, extra stall rest and time off work.

To learn more about Hallmarq Veterinary Imaging and standing MRI technology for horses:

© Fran Jurga and Hoofcare Publishing

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