The challenges of equine foot lameness

Foot pathologies are one of the most common causes of lameness in horses. Although localization of the lameness is, in most cases, easily achieved using diagnostic anesthesia, obtaining a complete and accurate diagnosis can be challenging.^1,2

With the recent advances in diagnostic imaging, in particular the increased availability of MRI and CT, we have improved our ability to diagnose changes that may not be so obvious on x-rays, particularly in the early stage of the disease. This, in return, has improved our treatment abilities and overall postoperative prognosis. In this article, we will discuss 2 conditions of the equine foot: keratomas and septic osteitis.³

Keratomas

Keratomas are often seen in practice, and they can be a diagnostic challenge. Keratomas are benign soft tissue occupying masses of the foot capsule and containing squamous epithelial cells infiltrated with keratin. They are commonly located in the dorsal, dorsolateral, or dorsomedial aspects of the foot, and as they become larger, they can put pressure on the distal phalanx, resulting in resorption of the bone. The associated poorly structured soft horn may be more susceptible to bacterial colonization and infection. Clinical signs of keratomas can range from being quiet and asymptomatic to causing various degrees of lameness, deformation of the hoof capsule/white line, and recurrent abscesses.¹

Diagnosis can be made using conventional x-rays, but more advanced imaging with CT has been the modality of choice for diagnosis and treatment of this condition (Figure 1a and Figure 1b). CT allows for a better delimitation of the lesion and, in return, improved planification of surgical treatment (Figure 2).^4,5

Treatment can be conservative if the patient is asymptomatic. However, all affected tissue may need to be surgically removed to prevent recurrence. Depending on the location and extent of the keratoma and the nature of the horse, the procedure can be performed while the horse is standing or under general anesthesia. Partial wall resection is associated with reduced postoperative complications, improved postoperative comfort, and a quicker return to exercise. Following the procedure and depending on the size of the defect, creating stabilization of the hoof wall either with a therapeutic shoe or fiberglass material is usually warranted.^6-9

Septic pedal osteitis

Another common condition is septic pedal osteitis, which is usually the result of a chronic foot abscess that extends to the third phalanx. In severe cases, formation of a sequestrum can be seen.^1,2 Sometimes patients will present with foot pain, and x-rays may not be entirely conclusive as to the extent of the pathology. Most patients will have a mild to moderate degree of lameness, increased digital pulses, and presence of a draining tract, and will be positive to hoof testers. Some patients may also present with subsolar abscesses nonresponsive to treatment.

Diagnosis is made based on clinical signs and x-ray images characterized by radiolucency of the distal phalanx and irregularity of the solar margin. Because the appearance of the solar margin in clinically normal horses varies widely and may take a couple of weeks to be evident, a CT or MRI may be indicated (Figure 3, Figure 4a and Figure 4b). CT may be more sensitive and offer a more complete diagnosis and treatment, especially if targeted debridement of the third phalanx is needed or a sequestrum needs removal (Figure 5a and Figure 5b). In more complicated cases, surgical debridement will be needed and can be achieved through a localized trephine hole over the lesion. Similar to keratoma removal, a smaller surgical access will allow for a better postoperative outcome.^10,11

For example, the case in Figure 5 is a horse that presented sound in walk, and 4/10 right hindlimb lame when trotted in a straight line. The horse was noted to have elevated right hind digital pulses but no notable swellings or effusions on the limb. The horse was anesthetized, and a CT scan of the right hind distal limb was performed to assess the extent of the devitalized bone and plan the surgical approach. Under the same anesthesia, the defect in the sole was enlarged, guided by the CT findings, and the sequestrum was identified and removed. Infected tissue (bone and laminar) was debrided. Regional limb perfusion with amikacin was performed prior to recovery. Once a healthy bed of granulation tissue was formed, a treatment plate was applied until the sole defect filled and healed.

Conclusion

CT can be extremely useful in the diagnosis and treatment of various conditions of the equine distal limb. If one of the main limitations until now was the necessity to place the horse under general anesthesia, the development of new units allowing the procedure to be performed with the horse standing will be an advantage and may lead to new indications for the procedure.

About the author: After graduating from the Ecole Nationale Veterinaire de Lyon, France, Mélanie Perrier, DrMedVetm DACVS, ECVS, CERP, completed an equine surgical internship in California, followed by a large animal surgery residency at The University of Wisconsin, Madison. Perrier was then a clinical assistant professor of large animal surgery and critical care at the University of Tennessee, Knoxville, before returning to private practice in the Middle East and France. Perrier is now a senior lecturer in equine surgery at the Royal Veterinary College, United Kingdom. Her main interests are soft tissue surgery, equine rehabilitation and management of the equine athlete.

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