Chronic lameness in a pony

Dorsopalmar and lateromedial views were made of both front feet. Because of the abnormal shape of the feet, opaque markers were placed on the hoof wall.

Radiographic changes

• Rotation of P3 bilaterally with minimal sign of "sinking" of P3.
• Gas between the hoof wall and laminar corium suggesting subsolar abscessation and septic osteitis.
• Bone lysis involving the tips of P3 as seen on the DP views suggesting septic osteitis.
• A break in the pastern angle bilaterally.
• Mineralization of the lateral cartilages of P3.

Radiographic diagnosis

• Bilateral chronic laminitis characterized by rotation of P3 with minimal "sinking".
• Probable associated bilateral P3 septic osteitis with subsolar absessation.

Comments

Radiographic signs of P3 displacement are definitive evidence of chronic laminitis. This includes either palmar deviation (rotation) of P3 from the hoof wall, distal (vertical or "sinking") displacement of P3, or a combination of the two.

Normally, the dorsal cortex of P3 is parallel to the dorsal margin of the hoof wall in the lateromedial view. Divergence of the hoof wall and the dorsal cortex is indicative of mechanical separation of the dermal and epidermal laminae. In the horse with palmar deviation of P3, these lines diverge at the toe region. The angle can be measured and is referred to as the degree of rotation.

Other radiographic changes seen with laminitis are gas between the hoof wall and the soft tissues of the laminar corium. Bony changes include an indistinct dorsal surface of P3, a "ski tip" appearance with or without pathologic fracture to the tip of P3 and enlarged vascular channels, all secondary to subsolar abscess and septic osteitis.

Distal displacement of P3 can be more difficult to detect. In the normal foot, the proximal edge of the extensor process of P3 is positioned roughly at the same plane or just proximal to the junction of the hoof wall and coronary band.

Other radiographic changes that can be seen with chronic and progressive laminitis include a very thin sole. A break in the pastern angle (rotation of P3 about the distal interphalangeal joint) can occur if contraction of the deep digital flexor tendon occurs or if the rapid growth of the hoof wall at the heel is improperly managed.

An increase in the thickness of the dorsal soft tissues has been suggested to be an early sign of laminar inflammation or edema and thus a sign of acute laminitis.

Measurements made from the radiographs are probably most valuable when used for serial assessment on an individual horse. Positioning of both the horse's foot and the x-ray beam is critical.

From The Phalanges, Elizabeth A. Riedesel, in (Thrall, Donald E. Textbook of Veterinary Diagnostic Radiology, 5th Edition)