Laminitis, Chronic
Basic Information 
Definition
• A painful inflammatory condition of the hoof-lamellar interface (HLI) that causes lameness, abnormal hoof growth and appearance, and separation of the hoof from underlying dermal connective tissue
• The HLI has been compromised by the laminitic condition.
• May or may not be associated with pain at any one time
• Acute laminitis evolves into chronic laminitis at some arbitrary point.
• There is evidence of abnormal hoof growth on physical examination.
• The development of chronic laminitis is an inescapable consequence of the acute laminitic condition, whatever the cause.
• When laminitic pain is diagnosed for the first time in a horse with hoof growth changes and radiographic abnormalities implicative for underlying chronic laminitis, the episode is usually referred to as subacute laminitis.
• Insidious-onset, chronic laminitis may result from underlying endocrinopathic influences such as insulin resistance or corticosteroid influence and is commonly identified in horses that have been grazing pastures (“pasture associated laminitis” [PAL]).
• Also classified depending on the clinical behavior of the condition over time
• Recurrent, exacerbative, or refractory (chronic) laminitis is characterized by repetitive and recurrent bouts of activated inflammation in the HLI that cause progressive deterioration of the integrity of the hoof and persistent pain.
• Chronic subacute laminitis refers to the situation in which pathologic changes in the HLI are recognized by the abnormal manner with which the affected hoof has grown but tends not to be so readily associated with pain and lameness.
Clinical Presentation
• Abnormal hoof growth is usually evident with or without pain (lameness).
• When present, lameness and hoof pain are similar to those described for acute laminitis (see “Laminitis, Acute” in this section).
• When exercised on hard ground, chronically affected horses are likely to develop bilateral forelimb lameness, and the digital arterial pulses become transiently prominent.
• Visual inspection of the hoof reveals prominent circumferential growth lines, palmar/plantar divergence of the growth lines, bunching up of growth lines at the dorsal aspect of the hoof, slippering of the toe, broadening of the white line zone (especially at the toe), seedy toe, solar convexity, and heel contracture.
• Conservative paring of the solar aspect of the hoof often reveals flecks of hemorrhage.
• The chronically foundered hoof is prone to developing recurrent sole abscesses.
Diagnosis 
• May be diagnosed several days after the development of painful acute laminitis (see “Laminitis, Acute” in this section)
• May also be diagnosed based on observation of characteristic physical abnormalities observed on examination of the hoof (see above) in the absence of overt signs of pain or lameness
• The patient may develop bilateral lameness and increased prominence in the digital arterial pulse strength when exercised on hard ground surfaces.
• Examine the patient for evidence of underlying predisposing endocrinopathy such as pituitary pars intermedia dysfunction (PPID) and equine metabolic syndrome (EMS).
• Endocrinologic tests performed on horses affected with laminitis may yield falsely positive results as a result of stress and pain (cortisol response and reduced insulin sensitivity).
Treatment 
General principles
• The two essential goals are pain management and restoration of the structural integrity of the hoof.
• The athletic capability of many affected horses will be reduced or nullified as a consequence of laminitis.
• Sometimes the prognosis for severe laminitis is unfavorable and warrants euthanasia.
• Emphasize to the owner that the prognosis may become clearer after some time has passed to allow the effects of treatment to be assessed and that treatment may be labor intensive and lengthy.
• Be cautious about enthusiastically encouraging horse owners to pursue treatment for severe laminitis without first discussing the fact that it might not be effective.
• Specific treatments for chronic laminitis are applied to the continuum of treatments started when acute laminitis first occurred.
• Treatments that must be addressed include both those pertaining to rehabilitation of the affected hoof and those that promote the general health of the patient.
• Treatment and management of chronic laminitis is usefully addressed under the following categories: rest and stall confinement, stabilization of P3, pain management, hoof trimming and farriery, surgical treatments, nutritional factors, endocrinopathic factors, and miscellaneous
• There are no validated reports for the predictably successful prevention or treatment of laminitis using drugs.
• Both rehabilitation of the affected hoof and the prognosis depend on new hoof growth. (The rate of new hoof growth along a chronically diseased HLI is slower than it is in the healthy horse.)
• When successful, the management of chronic laminitis typically requires at least 6 to 12 months of closely invested care.
Rest and stall confinement
• The patient’s movement should be restricted (large stall confinement) to minimize further mechanical damage and to promote healing of the HLI.
• Premature exercise (eg, as soon as signs of hoof pain have abated) often causes further damage to the HLI (and pain).
• Allow time to establish stability in the HLI akin to the value of stabilization during bone fracture repair.
• Limited and strictly regulated handwalking exercise should only be contemplated after evidence has been demonstrated that the HLI has stabilized (see below).
Stabilize P3
• Although it is not possible to completely stabilize P3 in the same manner that internal fixation techniques may be used to immobilize bone fractures, strategies aimed at promoting stability of P3 within the hoof capsule are helpful from the perspectives of both pain management and optimal healing (promoting reestablishment of the normal relationship between P3 and the hoof capsule).
• Effective stabilization of P3 inhibits further damage to the compromised HLI.
• Evaluation of the effectiveness of stability-promoting strategies includes observation of a reduction in pain (especially after pain medications such as phenylbutazone are withdrawn) and (objectively) the use of serially acquired hoof radiographs.
• Radiographic evidence of stability can be attributed to the effects of stability-promoting treatments as well as the effects of healing.
• Provision of stability is intended to relieve loading of the compromised aspects of the HLI (commonly at the dorsal aspect of the hoof) and redistribute loading to the more palmar/plantar aspects of the HLI and the ground-bearing surface of the hoof (sole and frog).
• Stability may also be promoted by reducing the turning force (“moment”) acting on the dorsal HLI by the pull of the deep digital flexor tendon (DDFT) through the distal interphalangeal joint.
• Reduction of the distal interphalangeal joint moment is not recommended for horses affected by distal displacement of the (entire) third phalanx (“sinking”).
• Stability promoting strategies include restriction of movement, removing the patient’s shoes (standing on regular shoes tends to increase tension in the HLI), and simply providing a deeply littered bedding.
• The provision of sand or pea gravel for bedding is often helpful.
• Patients should not be discouraged from lying down.
• Support to the sole or frog may also be provided in the form of high-density styrofoam cut to the shape of the hoof and attached using tape.
• Other commonly used treatments include the application of Lily pads to the frog, silicone putty, and plaster of Paris casts applied to fill in the concavities of the sole.
• The dorsal aspect of the wall at the toe should be beveled using a rasp to facilitate breakover.
• Specially designed reusable tape-on shoes (Redden modified Ultimate shoes) can be used in conjunction with silicone putty applied over the palmar/plantar aspect of the sole or frog to provide heel elevation (if indicated) to reduce the tensile pull of the DDFT and a “rolled” toe that serves to move the point of breakover to a more palmar/plantar location.
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