Equine laminitis

An update on aetiology, predisposing factors, molecular pathogenesis, advanced diagnostics and clinical management in a specialist facility.

1. Introduction

Laminitis is a complex syndrome characterised by structural failure of the distal suspensory apparatus of the third phalanx (P3), with compromise of the dermal and epidermal lamellae. Despite advances in our understanding of its pathogenic mechanisms, it remains one of the leading causes of chronic pain, suffering and, in many cases, euthanasia in the horse.

Speed of intervention is a primary prognostic determinant: clinical studies show that lamellar damage can occur within a few hours of the developmental phase, and that the therapeutic window for preventing rotation or sinking of P3 is extremely narrow (12–24 hours).

Equine veterinary clinics equipped with inpatient facilities and advanced diagnostics play a crucial role in managing acute and subacute cases, offering continuous monitoring, intensive support and the ability to perform investigations such as serial radiographs and venography, key diagnostic tools for guiding treatment.

2. Epidemiology and predisposing factors

2.1 Endocrinopathic laminitis (EL)

This is now recognised as the most frequent form (up to 90% of cases not associated with acute systemic disease).
Main predisposing conditions:

• Insulin dysregulation (ID)
• Equine Metabolic Syndrome (EMS)
• PPID (Cushing's), especially in horses >15 years old

Higher-risk categories:

• ponies (Shetland, Welsh), Iberian horses, Morgans
• obese animals (BCS >7/9) or those with regional adiposity (high cresty neck score)
• horses grazing pasture rich in NSC (Non Structural Carbohydrates)

2.2 Inflammatory or septic laminitis

Associated with conditions such as:

• acute colitis and endotoxaemia
• retained placenta
• acute metritis
• severe pneumonia
• bacterial endotoxin release syndrome

2.3 Mechanical laminitis

“Supporting limb laminitis” (SLL) is secondary to prolonged overloading of the contralateral limb, and is particularly frequent in:

• full-thickness fractures
• tenotomy or catastrophic injury of the deep digital flexor tendon (DDFT)
• joint sepsis or severe cellulitis

Its pathophysiology relates to chronic lamellar hypoxia and reduced vascular flow.

3. Pathogenesis: molecular and histopathological mechanisms

Laminitis is not a single disease process but a syndrome characterised by several overlapping pathogenic mechanisms.

3.1 Vascular dysfunction and lamellar microangiopathy

Studies by Pollitt and Belknap have demonstrated:

• initial vasoconstriction mediated by endothelins
• a subsequent increase in capillary permeability
• interlamellar oedema
• arteriovenous shunting
• collapse of the digital venous network

Impaired perfusion causes tissue hypoxia and activation of matrix metalloproteinases (MMP-2, MMP-9).

3.2 MMP activation and basement membrane degradation

MMPs degrade the basement membrane (BM), the key structural element anchoring the epidermal lamellae to the dermal lamellae.
Consequences:

• lamellar separation
• loss of P3 suspension
• rotation/sinking

3.3 Insulin dysregulation and IGF-1 pathways

In endocrinopathic laminitis:

• prolonged hyperinsulinaemia activates IGF-1 receptors on epidermal cells
• it stimulates disorganised keratinocyte proliferation
• it alters hoof mechanics
• it reduces cell cohesion

3.4 Systemic inflammation

Numerous inflammatory mediators are involved:

• TNF-α
• IL-1β, IL-6
• COX-2
• PGE2 (increased in the digital corium)

Neutrophil infiltration and microthrombosis are observed.

3.5 Biomechanical failure of the P3 suspensory complex

The combination of:

• BM degradation
• DDFT alterations
• loss of interlamellar cohesion
  results in progressive rotation of P3.

The pull of the DDFT tends to draw the apical margin of P3 dorsally, while body weight drives vertical sinking.

4. Clinical diagnosis and staging

4.1 Early clinical signs

• markedly increased digital pulse
• increased local temperature
• accentuated pain on hoof testers applied across the foot
• typical “sawhorse” stance (toe-out)
• stiff gait, reluctance or inability to walk

4.2 Obel staging (classical)

• I: mild signs, horse reluctant to move
• II: difficult movement, alternate lifting of the limbs
• III: marked refusal to move, resistance to limb flexion
• IV: immobile, extreme reluctance or inability to move

5. Advanced diagnostics

5.1 Radiographic diagnosis

Standard projections include:

• lateromedial with an external marker
• dorsopalmar/dorsoplantar
• skyline of the extensor process

Parameters to assess:

• rotation of the dorsal margin of P3
• sole–P3 distance (sole depth)
• coronary band–P3 distance (founder distance)
• vertical sinking
• dorsal hoof wall thickness

Serial radiographs every 48–72 hours in acute cases allow the clinician to monitor progression and adjust the treatment and shoeing plan.

5.2 Venography of the foot

Digital venography allows direct assessment of lamellar venous drainage.
Indications:

• acute cases that are difficult to interpret clinically
• suspected incipient sinking
• failure to respond to treatment
• decisions regarding therapeutic shoeing

Main areas assessed:

• coronary venous plexus
• dorsal venous plexus
• circumflex vessels
• tip zone
• venous plexus of the frog

Typical abnormalities:

• collapse of the circumflex vessels
• absent filling of the tip zone
• reduced or absent dorsal drainage
• signs of coronary ischaemia

Venography performed within 24 hours can dramatically change the prognosis and guide more targeted mechanical support.

6. Therapeutic management

6.1 Early intervention (first 12–24 hours)

Treatment in the early phases is decisive in preventing progression of the damage.

Continuous cryotherapy

The gold standard in preventing endocrinopathic laminitis and in the early phases.
Parameters:

• ideal temperature 0–5 °C
• duration: 24–72 continuous hours
  Cryotherapy suppresses MMP activity, reduces the inflammatory response and stabilises the microcirculation.

Pharmacological treatment

• NSAIDs: flunixin meglumine, phenylbutazone
• Pentoxifylline: to improve microcirculation
• Acepromazine: peripheral vasodilation (selective use)
• Insulin therapy for severe endocrinopathic forms (targeted use)

Immediate mechanical support

• EVA or variable-density polyurethane pads
• caudal support
• stabilising bandages
• immobilisation of the foot to reduce DDFT leverage

6.2 The importance of hospitalisation

Hospitalisation allows:

• 24-hour monitoring of the response to treatment
• prolonged, controlled cryotherapy
• management of refractory pain
• serial diagnostics (radiography, venography)
• intensive management of nutrition and insulin resistance
• application of advanced therapeutic shoeing through farrier–veterinarian collaboration
• controlled surfaces to limit movement

In severe cases, hospitalisation is the difference between functional recovery and irreversible progression.

6.3 Treatment of chronic forms

Objectives:

• mechanical stabilisation
• progressive realignment of P3
• metabolic management (weight management, low-NSC diet)
• corrective shoeing (heart bar, realignment shoeing, wedge shoe, advanced barefoot management)
• long-term pain control (gabapentin, targeted NSAIDs)

7. Prognosis

Negative prognostic factors:

• sinking >10–15 mm
• absent venous filling in the tip zone
• sole depth <10 mm
• rotation >12°
• uncontrollable pain
• severe, unmanageable metabolic conditions

The prognosis is better in cases diagnosed and treated within 24 hours.

 

IN DEPTH: Venography of the foot — detailed technique

Venography is an advanced diagnostic procedure that allows visualisation of the venous perfusion pattern within the horse's foot by injecting radiopaque contrast medium into the digital vein. It is particularly useful in the acute phases of laminitis to assess the degree of vascular compromise and guide the choice of therapeutic shoeing.

Patient preparation

• The horse is preferably sedated (xylazine or detomidine ± butorphanol) to ensure it stands still.
• The affected limb is lifted and placed on a radiographic block.
• It is essential to clip and disinfect the area over the lateral or medial digital vein to make catheter placement easier.

Catheter placement

• A 20–22 G catheter is used, inserted into the dorsal or lateral digital vein, just proximal to the bifurcation of the coronary veins.
• The catheter is secured with a suture or elastic tape to prevent displacement during the procedure.
• A tourniquet is applied just above the fetlock to raise venous pressure and promote filling of the distal vascular system.

Preparation of the foot

• The foot is thoroughly cleaned and dried.
• A radiolucent sleeve or light bandage is applied to contain any leakage of contrast medium.
• A standardised wooden or plastic radiographic block is used to keep the position constant.

Administration of the contrast medium

• Iopamidol or iohexol at 300–370 mg/ml is normally used.
• The recommended volume ranges between 20 and 30 ml depending on the size of the horse.
• The contrast medium must be injected at constant pressure, over 5–7 seconds, to ensure uniform filling of all the digital veins.
• The radiograph must be taken within 5–10 seconds of completing the injection, to avoid artefacts caused by proximal diffusion.

Recommended radiographic projections

• Lateromedial
• Dorsopalmar/dorsoplantar
• 60° medial and lateral obliques (optional)
• “Tip view” to assess the tip zone

Vascular structures to analyse

1. Coronary venous plexus
   Indicative of proximal perfusion: a reduction suggests coronary compromise or capsular tension.
2. Dorsal plexus
   Sensitive to changes in pressure and to rotation of P3.
3. Circumflex vessels
   Absent filling is a negative prognostic sign, correlated with ischaemia of the sole.
4. Tip zone
   One of the areas compromised earliest in endocrinopathic laminitis.
5. Veins of the frog
   These allow assessment of the integrity of the caudal blood supply and of the hoof–pastern axis.

Interpreting the results

Main signs of compromise:

• absent or reduced filling of the circumflex vessels
• lack of perfusion in the tip zone
• dorsal “cut-off” coinciding with rotation of P3
• coronary congestion with pathological venous dilation
• collapse of flow in the frog

Venography, if repeated at 12–24 hours, provides valuable information on the progression of vascular damage and allows specific supports to be guided (heart bar, wedge, caudal pads, wooden blocks).

IN DEPTH: Wooden hoof supports in the management of laminitis

Wooden hoof supports, such as the “Steward Clog”, “Wooden Clogs” or custom variants, are an established therapeutic approach in the management of acute and chronic laminitis. Their effectiveness derives from the combination of load redistribution, reduced DDFT leverage and stabilisation of the foot.

Biomechanical principles

1. Reduced dorsal leverage
   The wooden block has a profile that promotes early breakover, reducing tension on the DDFT.
2. Load redistribution towards the caudal region
   The rigid, flat material transfers load onto the digital cushion and frog, reducing pressure on the toe.
3. Stabilisation of the hoof capsule
   Uniform contact with the block improves cohesion between sole, wall and third phalanx.
4. Pain relief
   Many horses show immediate improvement in locomotion thanks to reduced instability.

Application technique

• The foot should be prepared minimally, avoiding excessive paring of the sole.
• The support is shaped from wood 2.5–4 cm thick.
• It is applied with screws and polyurethane adhesive (for example a high-viscosity product) to distribute load evenly.
• Reinforcements or bevels may be added at the sides to facilitate lateral roll.
• Cushioning material (EVA, silicone) can be incorporated under the caudal region in cases of intense pain.

Clinical indications

• acute phase of endocrinopathic laminitis
• laminitis with radiographically documented dorsal rotation of P3
• horses with thin soles
• horses that are difficult to shoe in the acute phase (as a temporary alternative to conventional shoeing)
• situations in which venography shows a deficit of the circumflex vessels

Advantages

• atraumatic application
• immediate reduction in leverage and pain
• can be modified and customised
• excellent synergy with cryotherapy and pharmacological treatment

Limitations

• they require frequent reassessment (every 2–3 weeks)
• not indicated in horses with fractures or marked instability of P3
• they require a flat, soft surface in the stable

8. Conclusions

Laminitis is a multisystemic, multifactorial condition requiring an integrated, multidisciplinary and highly prompt approach. Modern diagnostic techniques such as advanced radiography and venography have revolutionised the way the progression of lamellar damage is assessed, allowing more precise therapeutic decisions.

Hospitalisation in a specialist equine veterinary clinic remains a decisive element in the management of acute cases, ensuring constant monitoring, intensive treatment and adjustment of therapy according to clinical progression.

 

General bibliography

1. Pollitt, C. C. (2008). Equine laminitis: Current concepts. Equine Veterinary Journal, 40(4), 295–302.
2. Belknap, J. K., Black, S. J. (2012). Inflammatory pathways in laminitis. Veterinary Clinics of North America: Equine Practice, 28(1), 95–110.
3. De Laat, M. A., McGowan, C. (2016). Development of insulin-associated laminitis. Equine Veterinary Journal, 48(3), 330–338.
4. Van Eps, A. W. (2010). Continuous digital hypothermia in acute laminitis. Journal of Veterinary Internal Medicine, 24(1), 153–160.
5. Parks, A. H., O’Grady, S. E. (2003). Radiographic interpretation of the equine foot. Veterinary Clinics of North America: Equine Practice, 19(2), 307–328.
6. Rucker, A. (2010). Venography of the equine digit: Clinical interpretation and application. Equine Veterinary Education, 22(3), 125–134.
7. Karikoski, N. P., Patterson-Kane, J. C., et al. (2011). Pathophysiology of endocrinopathic laminitis. Equine Veterinary Journal, 43(2), 171–178.
8. Waguespack, R. W., Belknap, J. K. (2010). Cellular events in laminitis. Veterinary Clinics of North America: Equine Practice, 26(1), 57–66.
9. Patterson-Kane, J. C., Karikoski, N. P. (2011). Histopathology of laminitis. Equine Veterinary Journal, 43(1), 72–80.
10. Burns, T. A. (2019). Venography and perfusion abnormalities in equine laminitis. Journal of Equine Veterinary Science, 76, 1–11.

1. Rucker, A. (2010). Principles of venography: Technique and interpretation. Equine Veterinary Education, 22(3), 125–134.
2. Redden, R. F. (2003). The digital venogram: Clinical use and interpretation. Proceedings of the Bluegrass Laminitis Symposium, 128–145.
3. Parks, A. (2016). Clinical application of venography in acute laminitis. Journal of Equine Veterinary Science, 47, 89–97.
4. Baxter, G. M. (2020). Advanced imaging of the equine foot. Veterinary Clinics of North America: Equine Practice, 36(1), 45–62.

1. Steward, M. (2003). The wooden shoe: Biomechanics and clinical outcomes in equine laminitis. Proceedings of the American Association of Equine Practitioners, 49, 334–347.
2. Taylor, D., Caldwell, F. (2014). Mechanical principles of wooden clogs in acute laminitis. Journal of Equine Veterinary Science, 34(5), 677–685.
3. O’Grady, S. E. (2018). The role of therapeutic farriery in laminitis management. Veterinary Clinics of North America: Equine Practice, 34(2), 341–357.
4. Caldwell, F. (2020). Application and outcomes of the modified Steward Clog. Equine Veterinary Education, 32(6), 299–307.