How to Treat Severe Laminitis in an Ambulatory Setting

1. Introduction

Severe laminitis is generally a career-ending disease in the horse and is often life-threatening. It has been stated often by authoritative sources that laminitis remains the most controversial disease in equine veterinary medicine with regards to etiology, treatment, and prognosis^a  . The challenges faced by the veterinarian and the farrier are enormous and include not only treating a disease in which the etiology is poorly understood but also guiding and counseling the owner/trainer throughout the treatment process. The owner should be made aware of the difficulties associated with treating severe laminitis and the ethical considerations regarding the welfare of the horse.¹  The goal of the clinician is to relieve pain, prevent or limit additional damage to the lamellae, and improve function of the feet. The clinician is often limited in this respect, because it is the extent of the lamellar pathology (damage) that will limit the success of treatment and not the treatment regimen itself.²  Treatment is also complicated, because there is no proven or consistent treatment for laminitis; consequently, treatment regimens for both acute and chronic laminitis generally remain empiric and are based on the past experience of the attending clinician.¹  Each horse with laminitis should be approached on an individual basis by noting the predisposing cause, amount of instability, foot conformation, and structures of the foot that can be used to change the forces placed on the hoof.³ 

Most cases of acute laminitis do not go to a veterinary clinic or referral facility, because the shear act of moving and shipping a horse with unstable laminitis may worsen the existing condition. Initially, the necessary expertise, medical care, imaging, and farriery care can be provided at the farm on an ambulatory basis. Radiography is essential for diagnosis, assessment of foot conformation, and guidance of the initial hoof care. Additional benefits of treating the horse as an ambulatory patient are the familiarity of the horse’s usual surroundings and the owner/trainer being involved in assessing improvement or deterioration of the condition, because they will be more aware of the animal’s normal behavior. An acceptable outcome in all but the mildest cases of laminitis requires a team of dedicated individuals: veterinarian, farrier, and horse owner. This paper presents an overview of the treatment options available when treating severe laminitis in a non-hospital setting.

2. The Phases of Laminitis

The classification of laminitis into phases is a convenience to both enhance comprehension and assist in the diagnosis, treatment, and prognosis, but the disease is a continuum. Laminitis is divided into the developmental, acute, and chronic phases, all three phases of which are relevant to the treating clinician. However, the continuum varies greatly among cases, because they may take different entry points into the disease and thus, different paths after affected.⁴ The developmental stage of laminitis is the initial phase of the disease that begins with the original insult to the lamellae and ends with the onset of clinical symptoms such as pain, increased digital pulse, hoof-tester pain, and laminitic stance. The acute stage begins with the onset of clinical symptoms and is frequently cited as lasting 72 h or until displacement of the distal phalanx occurs, whichever is sooner.⁴ Chronic laminitis has been associated with continuation of clinical signs and/or a change in position of the distal phalanx within the hoof capsule; however, if the clinical signs of acute laminitis have not markedly improved within 48 –72 h, the horse should be considered to be entering the chronic stage. It should be noted that, in some horses with equine metabolic syndrome, there seems to be a derangement of the lamellae, and they remain painful for an extended period of time without displacement of the distal phalanx.
 

3. The Mechanism

The anatomic structure of the tissues affected by laminitis has been well-documented. However, despite considerable advances in our understating of the pathophysiology of laminitis made over the two decades, there is still much to be learned about the initiating events and the pathways by which they lead to the clinical disease. The interdigitating dermal and epidermal lamellae and their related vasculature are positioned between the parietal surface of the distal phalanx and the rigid hoof capsule. The digital circulation to the proximal dorsal lamellae is through the coronary artery, and the distal dorsal lamellae receive their blood supply from branches of the terminal arch that form the circumflex artery. Any compromise or instability in the lamellae changes the position of the distal phalanx, which in turn, creates abnormal pressure on the vessels restricting circulation. The inflexible nature of the hoof capsule does not accommodate the inflammatory effects, especially edema, that occur in the laminar tissue during laminitis—this scenario could be considered a type of compartment syndrome effect.

Knowledge of the biomechanics and forces exerted on the structures of the foot, including the lamellae, is critical to the clinicians when formulating a plan to counteract these forces. Because the lamellae suspend the distal phalanx within the hoof capsule and accept weight, this structure is subjected to an array of mechanical forces. The main forces are the weight (load) of the animal, which is opposed by the ground reaction force (GRF) and the moments (a moment is the product of the length of a lever arm and the force perpendicular to the lever arm) about the distal interphalangeal (DIP) joint, in which the moment generated by the GRF is opposed by that load generated by tension in the deep digital flexor tendon (DDFT) (Fig. 1).⁴ These normal mechanical forces exerted on the foot become detrimental with laminar compromise. A laminitic horse that is painful will be reluctant to move, and when not recumbent, the horse’s limbs will be approximately positioned as if in the mid-stance phase of the stride. The load (opposed by GRF) is located dorsal to the center of articulation and just behind and slightly medial to the apex of the frog on the ground surface of the foot.⁵ When the limb is loaded, the tensile forces in the DDFT create a moment, which unless opposed by an equal and opposite moment, causes rotation around the DIP joint. At breakover, the moment created by the DDF exceeds that created by the GRF. The tensions in the DDF are greater during the mid-stance phase of the stride than at rest, and they are further increased at the beginning of the breakover phase of the stride. The opposing moments generated by the GRF and the tension in the DDF lead to a distractive force within the dorsal lamellae. Dorsal capsular rotation is the most common form of displacement seen in laminitis, and it relates to the inability of the compromised lamellae to accept the load placed on the dorsal region of the foot during weight-bearing and breakover. [...]