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. <