Laminitis

Severe cases with outwardly visible clinical signs are known by the colloquial term founder, and progression of the disease will lead to perforation of the coffin bone through the sole of the hoof or being unable to stand up, requiring euthanasia.

The bones of the hoof are suspended within the axial hooves of ungulates by layers of modified skin cells, known as laminae or lamellae, which act as shock absorbers during locomotion.

A single severe laminitic episode or repeated, less severe episodes can, depending upon the degree of separation of dermal and epidermal laminae, lead to either rotation or sinking of the pedal bone, both of which result in anatomical changes in the position of the coffin bone with visible separation of the laminae, colloquially known as founder.

Also, ligaments attaching the collateral cartilages to the digit, primarily in the palmar portion of the foot, possibly contribute to a difference in support from front to back.

A severe "sinker" usually warrants the gravest prognosis and may, depending upon many factors, including the quality of aftercare, age of the horse, diet and nutrition, skill, and knowledge and ability of the attending veterinarian and farrier(s), lead to euthanasia of the patient.

Clinical signs at this time include bounding digital pulses, lameness, heat, and possibly response to hoof testing.

Compensated cases will have altered hoof structure, including founder rings, wide white lines, and decreased concavity to the sole.

Venograms will have relatively normal contrast distribution, including to the apex and distal border of the coffin bone, and the coronary band, but "feathering" may be present at the lamellar "scar.

Venogram will show "feathering" into the vascular bed beneath the lamellae, and there will be decreased or absent contrast material in the area distal to the apex of the coffin bone.

[9] Commonly known as road founder, mechanical separation occurs when horses with long toes are worked extensively on hard ground.

Road founder is also seen in overweight animals, particularly when hooves are allowed to grow long; classic examples are ponies on pasture board in spring, and pregnant mares.

However, the continual shifting of weight required to balance in a moving vehicle may enhance blood circulation, so some horsemen recommend trailering as an initial step in rehabilitation of a horse after long confinement.

[citation needed] Whilst diet has long been known to be linked to laminitis, there is emerging evidence that breed and body condition also play a role.

[14] Levels of hormones, particularly adiponectin, and serum insulin are also implicated, opening up new possibilities for developing early prognostic tests and risk assessments.

Additionally, radiographs also allow the visualization and evaluation of the hoof capsule, and can help detect the presence of a lamellar wedge or seromas.

[1] The lateral view provides the majority of the information regarding degree of rotation, sole depth, dorsal hoof wall thickness, and vertical deviation.

Poor or improper blood flow to different regions of the hoof help determine the severity of the laminitic episode.

[1] Other imaging tools have been used to show mechanical deviations in laminitis cases include computed tomography, as well as MRI, which also provides some physiologic information.

With modern therapies, most laminitics will be able to bear a rider or completely recover, if treated quickly, and if the laminitis was not severe or complicated (e.g. by equine metabolic syndrome or Cushing's disease).

Exercise is slowly increased once the horse has improved, ideally in an area with good (soft) footing, beginning with hand-walking, then turn-out, and finally riding under saddle.

[1] Cooling of the hoof in the developmental stages of laminitis has been shown to have a protective effect when horses are experimentally exposed to carbohydrate overload.

[1] Pentafusion, or the administration of ketamine, lidocaine, morphine, detomidine, and acepromazine at a constant rate of infusion, may be of particular benefit to horses suffering from laminitis.

[34] Besides pain management and control of any predisposing factors, mechanical stabilization is a primary treatment goal once the initial inflammatory and metabolic issues have resolved.

Once the distal phalanx rotates, it is essential to derotate and re-establish its proper spatial orientation within the hoof capsule, to ensure the best long-term prospects for the horse.

Trimming the heels helps to ensure frog pressure and increases surface area for weight-bearing on the back half of the hoof.

[38] While horses may stabilize if left barefooted, some veterinarians believe the most successful methods of treating founder involve positive stabilisation of the distal phalanx, by mechanical means, e.g., shoes, pads, polymeric support, etc.

The resulting comfort also reduces overall stress levels, leading to a faster recovery as the horse can quickly return to a regular routine.

If decreased bloodflow distal to the coronary plexus is seen on a venogram, or when a laminar wedge forms between P3 and the hoof wall, preventing the proper reattachment (interdigitation) of the laminae, this procedure may be beneficial.

This may lead to abscesses within the hoof capsule that can be severe and very painful, as well as a mass of disorganized tissue called a laminar (or lamellar) wedge.

[52] Complications to laminitis include recurrent hoof abscesses, which are sometimes secondary to pedal osteitis,[1] seromas, and fractures to the solar margin of the coffin bone.

Radiograph of a horse hoof showing rotation of the coffin bone and evidence of sinking, a condition often associated with laminitis. The annotation P2 stands for the middle phalanx , or pastern bone, and P3 denotes the distal phalanx, or coffin bone. The yellow lines mark the distance between the top and bottom part of the coffin bone relative to the hoof wall, showing the distal (bottom) of the coffin bone is rotated away from the hoof wall.
Hoof sagittal section with massive inflammation and rotation of third phalanx
Hoof specimen, sagittal section. Severe P3 rotation and penetration into the sole. A lamellar wedge is evident.
The front feet of this horse exhibit the rings and overgrowth typical of foundered horses.
Cross-section of horse with severe laminitis, showing a dished dorsal hoof wall that grows in a more horizontal manner, and a sole that is convex due to pressure from the tip of P3 secondary to rotation.
Radiographic measurements, including coronary extensor distance (CE), horn:lamellar distance (HL), sole depth (SD), digital breakover (DB), and palmar angle (PA)
The isolated event line showing a period of diminished dorsal growth, followed my normalised growth, is indicative of a fairly recent and well recovered bout of laminitis in this foot.