Keratomas in horses are abnormal growths or benign tumors that develop within the hoof capsule, potentially resulting in lameness and discomfort.

They develop slowly over time and may go unnoticed until they reach a size that interferes with the horse’s soundness.

These non-cancerous masses comprise overgrowths of keratin, typically forming near the coronary band. These masses are rare, and the exact cause of their development is unknown in most cases.

Treatment typically involves surgical removal of the keratoma. Most horses with keratomas make a full recovery and are able to continue in performance careers.

Keratomas in Horses

The hoof is a highly complex structure with many components working together to support the horse’s weight. Keratomas arise from the hoof keratin on the inner surface of the hoof wall, creating a mass between the hoof wall and the coffin bone. [1]

These large masses can compromise normal function of the hoof and damage surrounding tissues, resulting in pain and lameness.

Keratomas typically originate near the coronary band and extend downward. [2] They are usually cylindrical or spherical in shape, and are most commonly found near the toe or near the hoof quarters. [1][2] There are rare reports of keratomas affecting other locations, such as the hoof sole, frog, and above the coronary band. [1][3][4]

Most horses only have one keratoma, however there have been reports of multiple keratomas within one hoof, as well as horses with keratomas in multiple hooves. [3][4]

Causes

In most cases, the underlying cause of keratomas is unknown. [5] Some cases have a history of previous injury to the hoof, such as: [3][5]

  • Traumatic injury to the hoof, such as nail punctures or other foreign bodies
  • Sole abscesses
  • Imbalance in the hoof, causing abnormal stress on one area of hoof wall

Lameness from keratomas occurs due to the mass pressing against the highly sensitive laminae, the supportive tissue between the hoof wall and the coffin bone. [2] The mass pressing on surrounding tissues can also cause tissue death and damage to the coffin bone. [1][6]

Symptoms

The most common symptom of keratomas is intermittent, slowly progressive lameness. Most horses have moderate to severe lameness by the time of diagnosis. [5]

Additional symptoms include: [5][7]

  • Swelling or bulging of the coronary band or hoof wall
  • Deviation of the white line of the hoof towards the center
  • Appearance of a semicircular area of thickened, white tissue on the white line

The keratin composing a keratoma is generally of poor quality, and can become a site of fungal or bacterial invasion and infection. [8] These infections can result in a draining tract from the hoof sole or hoof wall, which can appear similar to a hoof abscess. [5]

Some horses with keratomas are only diagnosed when their owner brings them to the veterinarian due to recurring, difficult to treat hoof abscesses. [7]

Diagnosis

Since the symptoms of keratomas are similar to many other causes of lameness, a thorough diagnostic work-up is required to identify the cause. Diagnostic tests may include: [5]

  • Application of hoof testers
  • Flexion testing
  • Nerve or joint blocking
  • X-rays
  • Ultrasound

Most horses with keratomas show a pain response when the veterinarian applies hoof testers directly over the keratoma. [5]

They also typically show a significant improvement in their lameness with a palmar/plantar digital (PD) nerve block, which blocks the majority of the horse’s feeling in their hoof. [5] Some horses require an abaxial sesamoid nerve block to resolve their lameness, which blocks hoof pain sensation completely. [5]

Confirming a diagnosis of a keratoma requires X-rays, MRI, or CT scanning, which show the mass within the hoof capsule. [2][5] On X-rays, the mass appears as a semicircular shape over the coffin bone that has smooth edges. [5]

In some cases, keratomas are not visible on X-rays, requiring MRI or CT scanning for diagnosis. [7]

Treatment

Treatment of keratomas involves surgical removal of the growth, to resolve the pressure on the surrounding hoof structures. [5] The main surgical method is partial hoof wall resection, although other approaches can also be successful.

Surgery to remove a keratoma can be performed under general anesthesia or standing anesthesia, where the horse is sedated in a veterinary stock. [6] For standing procedures, the surgeon generally blocks the horse’s feeling in the affected foot using an abaxial sesamoid nerve block. [6]

Partial Hoof Wall Resection

In this surgical procedure, the surgeon first performs X-rays, MRI, or CT scanning to identify the exact location and size of the keratoma. [2]

After appropriate sedation, the surgeon cuts a window into the hoof wall using an oscillating saw or a hole-making device called a trephine. [2][6] The goal is to position the window directly over the keratoma, to remove the mass while maintaining as much intact hoof wall as possible. [6]

The major benefit of partial hoof wall resection is maintaining hoof wall stability, resulting in fewer post-operative complications. [9] Horses can also return to performance and exercise sooner compared to horses who receive a complete wall resection. [9]

Complete Hoof Wall Resection

This approach is more common for very large keratomas, or keratomas where the exact location of the mass is unknown. [6] In this procedure, the surgeon removes the entire hoof wall over top of the keratoma extending from the coronary band to the sole. [6]

By removing an entire section of hoof wall, the surgeon can clearly visualize the keratoma to ensure that the entire mass is removed. [6] They are also able to remove any dead or dying bone or tissue surrounding the keratoma. [6]

New Techniques

There is a report of successful removal of two keratomas through a supracoronary approach, or entering through the skin above the coronary band. [10]

The veterinarians reported decreased stall rest time and decreased time to returning to exercise from this approach, as it does not create any defects in the hoof wall. [10]

However, the usefulness of this approach is likely limited to keratomas close to or above the coronary band, as keratomas lower in the hoof would be inaccessible. [10]

Post-operative Care

Before the horse wakes up from anesthesia, the hole in the hoof wall is packed with gauze to help stabilize the hoof. [6] In some cases, the veterinarian may soak the gauze in antiseptic to reduce the risk of post-operative infection. [6]

Initial post-operative care typically involves bandage changes every 2-3 days for around 3-4 weeks. [6] Some surgeons recommend applying increasing concentrations of iodine to help dry out the hoof tissue and increase cornification, the process of producing keratin. [6] Horses may require antibiotics and pain control during this healing period. [6]

Stall Rest

During the initial recovery period, the horse must be on stall rest to prevent instability and damage within the hoof. [6]

Most horses require 4-6 weeks of stall rest until hole has closed over with a thin layer of keratin. [6] At this point, horses can begin a light exercise program under the guidance of their veterinary surgeon.

Recovery

Complete regrowth of the hoof wall defect typically takes 6-12 months, depending on environmental conditions. [6] In general, hoof wall grows approximately 6 mm/month, however this growth rate is slower during cold temperatures and in dry conditions. [5]

Once the hoof wall has regrown completely, the horse can return to its previous performance level in most cases.

Hoof Support

Horses that have a complete hoof wall resection require additional post-operative care to maintain the stability of the hoof.

The most common way to improve stability is a specialized horseshoe with wide clips on either side of the removed hoof wall. This keep the two halves of the hoof from separating when the horse’s weight is applied to the hoof. [6] These shoes must be reset every 6-8 weeks, similar to a standard horseshoe. [6]

Once the initial thin layer of hoof wall has rejoined the sole, a regular horseshoe can be used. [6]

Surgeons may also place a metal plate across the hoof wall defect as an additional support measure. [6] These plates are left in place until the new hoof wall grows in, and are only removed once the plate reaches the bottom of the horse’s hoof. [6] Alternatives to metal plates that are also common include plastic tabs or fiberglass patches. [9]

Horses that do not have adequate hoof support are likely to develop hoof cracks due to the weak hoof wall. [9] Horses that develop hoof cracks usually require longer periods of stall rest, and may have a delayed return to performance compared to other horses. [9]

They are also predisposed to developing excessive granulation tissue (proud flesh) while healing. [9] Treatment of excessive proud flesh usually requires a second surgical procedure to remove the excess tissue, to prevent impaired growth of the hoof wall. [9]

Hoof Reconstruction

Some surgeons may offer reconstruction of the hoof wall defect using polymethylmethacrylate, a specialized polymer that can replace the missing hoof keratin. [6][9] This reconstruction can allow the horse to return to exercise and performance sooner than traditional treatment options. [6]

Generally, these polymers are only applied once the initial keratin layer has grown in completely. [6] Applying polymers to a fresh surgical site poses a risk of trapping bacteria or dead tissue beneath the polymer, resulting in infection. [6][9]

Some antibiotic-containing polymers are available and can be used on fresh surgical sites at the surgeon’s discretion. [6]

New Techniques

A recent study used a 3D printed polylactic acid scaffold to apply a platelet-rich plasma (PRP) gel to healing keratoma surgical sites. [11] Platelet-rich plasma is commonly used to accelerate soft tissue repair and healing in lameness cases, as it contains products that increase tissue repair and proliferation. [11]

The use of PRP gel in keratoma treatment may help accelerate hoof wall growth and healing of the underlying tissues. [11] PRP also has antibacterial properties that may reduce the risk of infections. [11]

The researchers also believe that the scaffold used to hold the gel may provide an additional benefit for the regrowing hoof tissue by providing structural support for the growing cells. [11]

From their study, the researchers concluded that this new method may improve recovery times and complications from keratoma surgery. [11] Further research and more widespread availability of the polylactic acid scaffold is required before this treatment will become commonplace in veterinary surgical centers.

Prognosis

Most horses make a full recovery from keratoma surgery and return to their previous level of performance. [2][5]

One study showed that 83% of horses treated surgically returned to previous performance levels. [2] Typically, a return to performance takes between 6-36 months, depending on the size of the hoof wall defect. [11]

Some veterinarians and owners may elect medical management using pain control alone rather than undergoing hoof surgery. These horses have a poorer prognosis, with one study showing only 42% of horses successfully returning to performance. [2]

Recurrence

There is a possibility of the keratoma recurring if the mass is not completely removed during surgery. [5] Masses that have an irregular shape or poorly defined edges have a higher risk of recurrence. [12]

Using CT scanning or MRI may reduce the risk of leaving a portion of the keratoma behind, as these imaging modalities can more accurately identify the size and location of the lesion. [2]

Differential Diagnoses

Although keratomas are the most common mass occurring within the hoof capsule, there are other possible masses that can occur. To distinguish between the types of masses, a biopsy or submission of the removed mass to a diagnostic laboratory is required.

Other potential types of hoof masses include: [7][13]

  • Squamous cell carcinomas
  • Melanomas
  • Glomus smooth cell tumours
  • Mast cell tumours
  • Vascular hamartomas

Symptoms and treatment of these other masses are similar to keratomas, however some of these masses have a poorer prognosis. [7] For example, melanomas have a high risk of recurrence even after surgical removal. [13]

Summary

  • Keratomas in horses are an overgrowth of hoof keratin that can cause lameness and tissue damage
  • Symptoms include progressive lameness and changes in the hoof shape
  • Surgical removal of the mass is the most effective treatment option
  • Most horses make a full recovery and return to previous levels of performance

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References

  1. O’Grady. S. E. and Horne. P. A., Lameness Caused by a Solar Keratoma: A Challenging Differential Diagnosis. Equine Veterinary Education. 2001. doi: 10.1111/j.2042-3292.2001.tb01894.x.
  2. Baxter. G. M., Ed., Adams and Stashak’s lameness in horses, Seventh edition. Hoboken, NJ: Wiley-Blackwell, 2020.
  3. Miller. S. M. and Katzwinkel. R. H., Solar Keratoma: An Atypical Case. Journal of the South African Veterinary Association. 2015. doi: 10.4102/jsava.v86i1.1257.
  4. McDiarmid. A., Keratoma from the Frog Corium of a Horse. Equine Veterinary Education. 2007. doi: 10.2746/095777307X204207.
  5. Baxter. G. M., Ed., Manual of Equine Lameness. Wiley Blackwell, 2011.
  6. Honnas. C. M. et al., Hoof Wall Surgery in the Horse: Approaches to and Underlying Disorders. Veterinary Clinics of North America: Equine Practice. 2003. doi: 10.1016/S0749-0739(03)00002-6.
  7. Osborne. C. et al., Neoplasia within the Equine Foot: A Retrospective Case Series of Four Horses. Equine Veterinary Education. 2022. doi: 10.1111/eve.13523.
  8. Fürst. A. E. and Lischer. C. J., Other Clinical Problems of the Equine Foot. Veterinary Clinics of North America: Equine Practice. 2021. doi: 10.1016/j.cveq.2021.08.005.
  9. Smith. S. J. B. et al., Complete and Partial Hoof Wall Resection for Keratoma Removal: Post Operative Complications and Final Outcome in 26 Horses (1994–2004). Equine Veterinary Journal. 2006. doi: 10.2746/042516406776563288.
  10. Gasiorowski. J. C. et al., Supracoronary Approach for Keratoma Removal in Horses: Two Cases. Equine Veterinary Education. 2011. doi: 10.1111/j.2042-3292.2010.00197.x.
  11. Leonardi. F. et al., Platelet-Rich Plasma Combined With a Sterile 3D Polylactic Acid Scaffold for Postoperative Management of Complete Hoof Wall Resection for Keratoma in Four Horses. Journal of Equine Veterinary Science. 2020. doi: 10.1016/j.jevs.2020.103178.
  12. Mair. T. S. and Linnenkohl. W., Low-Field Magnetic Resonance Imaging of Keratomas of the Hoof Wall. Equine Veterinary Education. 2012. doi: 10.1111/j.2042-3292.2011.00367.x.
  13. Stefanik. E. et al., From Keratoma to Anaplastic Malignant Melanoma in a Horse’s Hoof. Animals. 2022. doi: 10.3390/ani12223090.