Pedal Osteitis in Horses
Pedal osteitis is a radiographic finding of demineralization of the solar margin of the distal phalanx, commonly associated with widening of vascular channels near the solar margin, which is best observed on a 65° proximal-distal dorsopalmar radiographic view. Although the term is usually used to describe changes in the dorsal distal (toe) solar margin, it can be used to describe bone resorption of any aspect of the solar margin of the distal phalanx. The bony resorption usually occurs due to chronic or repeated pressure and/or inflammation of the affected region. The resorption can be focal due to a focal lesion such as a keratoma, or it can be more diffuse in states such as chronic toe bruising, in which the entire distal margin of the toe may appear “moth-eaten” due to extensive bone resorption at the solar margin. Resorption in the toe region commonly occurs in chronic laminitis cases in which displacement of the distal phalanx results in inadequate sole depth between the ground surface and solar margin of the distal phalanx, resulting in chronic trauma and inflammation of that region of the phalanx and surrounding soft tissue (ie, sole bruising or chronic subsolar sepsis). Because the bone resorption is usually permanent, the radiographic finding does not indicate current pathology and may be due to a pathologic state that occurred years ago. Therefore, it is essential that a thorough examination be performed, including application of hoof testers to the entire solar margin of the foot and a lameness examination with nerve blocks if lameness exists. (The entire solar surface, including the toe, will be anesthetized with a palmar digital nerve block.)
Navicular disease is an important differential diagnosis to pedal osteitis–associated toe bruising, because toe bruising is also commonly bilateral and both conditions respond to a palmar digital nerve block. Radiography is helpful in diagnosis and in differentiation from navicular disease. Pedal osteitis associated with chronic subsolar abscess is usually aseptic, with the sepsis isolated to the soft tissue. Radiographic signs of sequestration or severe focal lucency in the same region as the subsolar sepsis may indicate septic pedal osteitis, but lucency can also be an artifact caused by subsolar gas once an abscess is drained (an unopened abscess usually has a tissue density). Curettage of the affected distal phalanx should be avoided unless it is documented to be septic.
Local treatment (ie, curettage of the affected area) is necessary only if there is an active septic process associated with the radiographic changes of pedal osteitis. General treatment of nonseptic cases should be directed at the primary disease that caused the resorption (eg, corrective shoeing for chronic laminitis cases with distal phalanx displacement that predisposes to solar margin bruising).