thumb|300px|[[Radiograph of a horse hoof showing marked separation of the hoof from the coffin bone with evidence of rotation and sinking, compatible with active severe laminitis. P2 designates the middle phalanx, or pastern bone, and P3 designates 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 marked widening of the hoof-lamellar zone, with the distal (bottom) of the coffin bone rotated away from the hoof wall.]]
Laminitis is a disease of the feet of ungulates, found mostly in horses and cattle involving inflammation of the laminae. Clinical signs include foot tenderness progressing to inability to walk, increased digital pulses, and increased temperature in the hooves. 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, often requiring euthanasia.
Laminae
The bones of the hoof are suspended within the hooves of ungulates by layers of modified skin cells, known as laminae or lamellae, which suspend the bony column from the hoof wall, contributing to shock absorption during locomotion. In horses, there are about 550–600 pairs of primary epidermal laminae, each with 150–200 secondary laminae projecting from their surface. These interdigitate with equivalent structures attached to the surface of the coffin bone (PIII, P3, the third phalanx, pedal bone, or distal phalanx), known as dermal laminae. The secondary laminae contain basal cells which attach via hemidesmosomes to the basement membrane. The basement membrane is then attached to the coffin bone via the connective tissue of the dermis. A severe inflammatory event is thought to damage the basal epithelial cells, resulting in dysfunction of the hemidesmosomes and subsequent reduction in adherence between the epithelial cells and the basement membrane. Most cases of laminitis occur in both front feet, but laminitis may be seen in all four feet, both hind feet, or in cases of support limb laminitis, in a single foot. In these cases, there is an increase in blood flow to the hoof, bringing in damaging substances and inflammatory cells into the hoof.
;Endocrinopathy
Endocrinopathy is usually the result of improper insulin regulation, and is most commonly seen with pituitary pars intermedia dysfunction (also called equine Cushing's syndrome) and equine metabolic syndrome (EMS), Since the basement membrane is the main link between the hoof wall and the connective tissue of P3, it is thought that its destruction results in their separation. However, contradictory evidence indicates the role of histamine in laminitis has not been conclusively established.
Mechanical separation
Commonly known as road founder, mechanical separation occurs when horses with long toes are worked extensively on hard ground. The long toes and hard ground together contribute to delayed breakover, hence mechanical separation of the laminae at the toe. Historically, this was seen in carriage horses bred for heavy bodies and long, slim legs with relatively small hooves; their hooves were trimmed for long toes (to make them lift their feet higher, enhancing their stylish "action"), and they were worked at speed on hard roads. 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. A notable example is the 2006 Kentucky Derby winner Barbaro.
Transport laminitis sometimes occurs in horses confined in a trailer or other transportation for long periods of time. Historically, the most extreme instances were of horses shipped overseas on sailing ships. 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.
Laminitis has been observed following an equine standing in extreme conditions of cold, especially in deep snow. Laminitis has also followed prolonged heating such as may be experienced from prolonged contact with extremely hot soil or from incorrectly applied hot-shoeing.
Complex causes
- Pituitary pars intermedia dysfunction, or Cushing's disease, is common in older horses and ponies and causes an increased predisposition to laminitis.
- Equine metabolic syndrome is a subject of much new research and is increasingly believed to have a major role in laminitis. It involves many factors such as cortisol metabolism and insulin resistance. It has some similarities to type II diabetes in humans. In this syndrome, peripheral fat cells synthesise adipokines which are analogous to cortisol, resulting in Cushings-like symptoms.
- A retained placenta, if not passed completely after the birth of a foal, can cause mares to founder, whether through toxicity, bacterial fever, or both.
- Anecdotal reports of laminitis following the administration of drugs have been made, especially in the case of corticosteroids. The reaction may be an expression of idiosyncrasy in a particular patient, as many horses receive high dose glucocorticoid into their joints without showing any evidence of clinical laminitis.
- Even horses not considered to be susceptible to laminitis can become laminitic when exposed to certain agrichemicals. The most commonly experienced examples are certain herbicides and synthetic nitrate fertilizer.
Risk factors
Whilst diet has long been known to be linked to laminitis, there is emerging evidence that breed and body condition also play a role. Levels of hormones, particularly adiponectin, and serum insulin are also implicated, opening up new possibilities for developing early prognostic tests and risk assessments.
Diagnosis
Early diagnosis is essential to effective treatment. However, early outward signs may be fairly nonspecific. Careful physical examination typically is diagnostic, but radiographs are also very useful.
Clinical signs
thumb|250px|right|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.
- Increased temperature of the wall, sole and/or coronary band of the foot
- Obel grade 1: Horse shifts weight between affected feet or continuously lifts feet up. It is sound at the walk but displays a shortened stride at the trot.
- Obel grade 2: Horse displays a stilted, stiff gait, although is willing to walk. It is possible to easily lift a front foot and have the horse take all of its weight on the contralateral limb.
- Obel grade 3: Horse displays a stilted, stiff gait, but is reluctant to walk and is difficult when asked to lift a front foot.
- Obel grade 4: Horse is very reluctant to move, or is recumbent.
;Nerve blocks
Horses suffering from the disease usually require an abaxial sesamoid block to desensitize the affected region, since the majority of pain comes from the hoof wall. However, chronic cases may respond to a palmar digital block since they usually have primarily sole pain. A 65-degree dorsopalmar view is useful in the case of chronic laminitis to evaluate the rim of the coffin bone for pathology.
Prognosis
The sooner the diagnosis is made, the faster the treatment and the recovery process can begin. Rapid diagnosis of laminitis is often difficult, since the general problem often starts somewhere else in the horse's body. 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). Even in these cases, a clinical cure can often be achieved. Endotoxic laminitis (e.g. after foaling) tends to be more difficult to treat. Successful treatment requires a competent farrier and veterinarian, and success is not guaranteed. A horse can live with laminitis for many years, and although a single episode of laminitis predisposes to further episodes, with good management and prompt treatment it is by no means the catastrophe sometimes supposed: most horses suffering an acute episode without pedal bone displacement make a complete functional recovery. Some countermeasures can be adopted for pasture based animals. Discovery of laminitis, either active or relatively stabilized, on an equine prepurchase exam typically downgrades the horse's value, as the possibility of recurrence is a significant risk factor for the future performance of the horse.
Several radiographic abnormalities can be judged to correlate with a worsened prognosis:
- Increased degree of rotation of P3 relative to the dorsal hoof wall (rotation greater than 11.5 degrees has a poorer prognosis) A chronic situation can be either stable or unstable. The difference between acute, chronic, stable, and unstable is of vital importance when choosing a treatment protocol. There is no cure for a laminitic episode and many go undetected. Initial treatment with cryotherapy and anti-inflammatory drugs may prevent mechanical breakdown if instituted immediately, but many cases are only detected after the initial microscopic damage has been done. In cases of sepsis or endotoxemia, the underlying cause should be addressed concurrently with laminitis treatment. Cryotherapy reduces inflammatory events in the lamellae. Ideally, limbs should be placed in an ice bath up to the level of the knee or hock. Hooves need to be maintained at a temperature less than 10 degrees Celsius at the hoof wall, for 24–72 hours. He eventually recovered enough to win two Grade 1 races before retiring to stud.
Drug therapies
;Anti-inflammatories and analgesics
Anti-inflammatories are always used when treating acute case of laminitis, and include Nonsteroidal anti-inflammatory medications (NSAIDS), DMSO, pentoxpfylline, and cryotherapy. However, firocoxib provides less pain relief than phenylbutazone or flunixin. Systemic acepromazine as a vasodilator with the fringe benefit of mild sedation which reduces the horse/pony's movements and thus reduces concussion on the hooves, may be beneficial after lamellar damage has occurred, although no effects on laminar blood flow with this medication have been shown. Nitroglycerine has also been applied topically in an attempt to increase blood flow, but this treatment does not appear to be an effective way to increase blood flow in the equine digit.
Trimming and shoeing
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. No approach has been shown to be effective in all situations, and debate is ongoing about the merits and faults of the numerous techniques. 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. With correct trimming and, as necessary, the application of orthotics, one can effect this reorientation. However, this is not always completely effective.
;Trimming
Successful treatment for any type of founder must necessarily involve stabilization of the bony column by some means. Correct trimming can help improve stabilization. This usually includes bringing the "break over" back to decrease the fulcrum-effect that stresses the laminae. Trimming the heels helps to ensure frog pressure and increases surface area for weight-bearing on the back half of the hoof. 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. Pour-in pads or putty is sometimes placed on the sole to increase surface area for weight-bearing, so that the sole in the area of the quarters, and the bars, will take some of the weight.
;Altering the palmar angle
The deep digital flexor tendon places a constant pull on the back of the coffin bone. This is sometimes counteracted by decreasing the palmar angle of the hoof by raising the heels, often with the use of special shoes which have a wedge in the heel of approximately 20 degrees. Shoes are usually glued or cast onto the foot so painful nailing does not have to take place. The position of P3 within the hoof is monitored with radiographs. Once the horse has improved, the wedge of the shoe must be slowly reduced back to normal.
;Use of orthotics
The application of external orthotic devices to the foot in a horse with undisplaced laminitis and once displacement has occurred is widespread. Most approaches attempt to shift weight away from the laminae and onto secondary weight-bearing structures, while sparing the sole.
;Corrective hoof trimming
Corrective hoof trimming will restore proper hoof form and function. Corrective trimming will allow the hooves to be healthy again.
;Realigning trimming
Realigning trimming trims back the toe so that it is in line with the coffin bone. Realigning trimming pushes the coffin bone back into the correct position. The process of a new hoof capsule totally growing out to replace the old one takes up to a year.
Alternative horseshoeing methods
New non-invasive horseshoeing methods are available for farriers to take advantage of. They encapsulate the damaged hoof, protecting and supporting the sensitive internal structures. This prevents further deterioration, whilst also immediately reducing pain and improving the horse's ability to move. The resulting comfort also reduces overall stress levels, leading to a faster recovery as the horse can quickly return to a regular routine.
Aggressive therapies
;Dorsal hoof wall resection
A dorsal hoof wall resection may help in certain conditions after consultation with an experienced veterinarian and farrier team. 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. When the coffin bone is pulled away from the hoof wall, the remaining laminae will tear. 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.
;Coronary grooving
Coronary grooving involves removing a groove of hoof wall just distal to the coronary band. It is thought to encourage dorsal hoof wall growth and improve alignment of the wall. Tenotomy does risk subluxation of the distal interphalangeal joint (coffin joint),
Complications
Complications to laminitis include recurrent hoof abscesses, which are sometimes secondary to pedal osteitis,