Equine Lameness Study Guide

Overview and Clinical Importance

Lameness is the most common clinical problem in equine practice and represents a significant portion of NAVLE questions. Defined as any alteration in normal gait or stance, lameness is typically caused by pain but may also result from mechanical or neurological dysfunction. The equine industry loses over $500 million annually due to lameness-related issues, making proficiency in lameness evaluation essential for every veterinarian.

Understanding the systematic approach to lameness examination, localization techniques, and common conditions affecting the equine musculoskeletal system is critical for both clinical practice and board examination success.

AAEP Lameness Grading Scale

The American Association of Equine Practitioners (AAEP) developed a standardized 0-5 lameness grading scale for consistent documentation and communication.

The Lameness Examination

A systematic lameness examination is essential for accurate diagnosis. The examination should follow a consistent sequence to ensure no components are missed.

Components of the Lameness Examination

1. History Taking

Key historical information includes: duration and onset of lameness (acute vs. chronic), progression pattern, effect of exercise, previous treatments, shoeing history, recent changes in work or management, and any concurrent systemic illness.

2. Visual Examination at Rest

Evaluate conformation, symmetry, muscle atrophy, swelling, abnormal stance, and obvious injuries. Horses with navicular syndrome may point the affected foot. Severe lameness may cause weight-shifting between limbs.

3. Palpation

Systematically palpate all limbs for heat, pain, swelling, and joint effusion. Compare contralateral limbs. Assess range of motion of all joints. Use hoof testers to evaluate sole and frog sensitivity.

4. Gait Evaluation

Observe the horse at walk and trot on a firm, level surface in straight lines and circles. The trot is the most useful gait for lameness evaluation because it is a symmetrical two-beat gait. Evaluate on both hard and soft surfaces.

Recognizing Forelimb vs. Hindlimb Lameness

Flexion Tests

Flexion tests are provocative tests that apply stress to joints and surrounding soft tissues for 30-90 seconds, followed by immediate trotting evaluation. A positive response (increased lameness) suggests pain in the flexed region.

Exam Focus: Flexion tests are NON-SPECIFIC - they stress multiple structures simultaneously. A positive response localizes pain to a region but does not identify the specific structure. Always follow with diagnostic analgesia and imaging.

Diagnostic Analgesia (Nerve Blocks)

Diagnostic analgesia is the cornerstone of lameness localization. Local anesthetic (typically mepivacaine 2%) is injected either perineurally (around nerves) or intrasynovially (into joints/bursae) to temporarily eliminate pain from specific regions.

Principles of Nerve Blocking

• Always block from DISTAL to PROXIMAL (start at the foot, work upward)
• Evaluate response within 10-15 minutes for distal limb blocks
• Allow 20-40 minutes for proximal limb/large nerve blocks
• Test skin sensation before reevaluating lameness
• NEVER perform nerve blocks if fracture is suspected

Common Nerve Blocks

Common Causes of Equine Lameness

Navicular Syndrome (Caudal Heel Pain)

Navicular syndrome is a degenerative condition affecting structures of the navicular apparatus including the navicular bone, navicular bursa, collateral sesamoid ligaments, distal impar ligament, and deep digital flexor tendon. It accounts for up to one-third of all chronic forelimb lamenesses.

Signalment and Predisposition

• Quarter Horses, Thoroughbreds, and Warmbloods most commonly affected
• Middle-aged horses (7-14 years)
• Almost always affects FORELIMBS and is usually BILATERAL

Clinical Signs

• Bilateral forelimb lameness (may appear as poor performance or shortened stride)
• Pointing of the affected foot at rest
• Landing toe-first rather than heel-first
• Lameness worse on hard ground and small circles
• Hoof tester sensitivity over the frog and heels
• Contracted heels; upright foot conformation

Diagnosis

• Marked improvement with palmar digital nerve block
• Radiographs: enlarged synovial fossae, osteophytes, flexor cortex erosions, medullary sclerosis
• MRI is gold standard - evaluates both bone and soft tissue structures

Treatment

Laminitis

Laminitis is a catastrophic disease involving failure of the dermal-epidermal bond (laminar attachment) between the hoof wall and the distal phalanx. It is a medical emergency with potentially life-threatening consequences.

Etiology

• Endocrinopathic (most common): Equine Metabolic Syndrome (EMS), Pituitary Pars Intermedia Dysfunction (PPID/Cushing's); hyperinsulinemia is key factor
• Sepsis/SIRS: Colitis, pleuropneumonia, metritis, grain overload, duodenitis/proximal jejunitis
• Support Limb (Contralateral): Excessive weight-bearing due to severe lameness in opposite limb
• Other: Corticosteroid administration (controversial); black walnut shavings exposure

Clinical Signs

• Classic 'sawhorse' stance - weight shifted to hindlimbs, forelimbs camped forward
• Bounding digital pulses (both forelimbs usually affected)
• Heat in the hoof wall
• Reluctance to move; 'walking on eggshells' gait
• Increased recumbency in severe cases
• Chronic signs: Divergent hoof rings, stretched white line, dropped sole, founder rings

Radiographic Findings

• Rotation: Increased angle between dorsal P3 surface and dorsal hoof wall (greater than 2-3 degrees abnormal)
• Sinking/Distal Displacement: Coffin bone moves distally within hoof capsule; decreased coronary band-extensor process distance
• Gas lucencies: Air tracking along separated laminae

Treatment

Memory Aid - LAMINITIS CAUSES: 'GRAPES'

G - Grain overload

R - Retained placenta

A - Anterior enteritis (and other GI disease)

P - PPID/Pituitary dysfunction

E - EMS/Endocrine disease

S - Support limb (contralateral limb laminitis)

Hoof Abscess (Subsolar Abscess)

Hoof abscess is the MOST COMMON cause of acute, severe (Grade 4-5) lameness in horses. It is a focal accumulation of purulent material between the germinal and keratinized epithelium of the hoof.

Etiology

• Bacteria enter through microcracks, white line separation, or penetrating wounds
• 'Hot nail' - horseshoe nail penetrating sensitive laminae
• Deep bruising; white line disease
• Horses with chronic laminitis are predisposed

Clinical Signs

• Sudden onset, severe UNILATERAL lameness (Grade 4-5)
• Horse may appear 'fracture lame'
• Increased digital pulse (single limb)
• Heat in affected hoof
• Focal sensitivity to hoof testers
• May drain at coronary band if not addressed ('gravel')

Diagnosis and Treatment

• Hoof testers localize area of sensitivity
• Explore sole with hoof knife - black tract/purulent material confirms diagnosis
• Establish VENTRAL DRAINAGE - open tract just enough for drainage; avoid excessive paring
• Soak foot in warm Epsom salts; poultice to draw infection
• Tetanus prophylaxis
• Antibiotics usually NOT needed unless cellulitis develops

Exam Focus: When presented with sudden onset, severe UNILATERAL lameness with increased digital pulse and hoof tester sensitivity - think HOOF ABSCESS first. Relief is dramatic within 12-24 hours once drainage is established. If fracture is suspected, do NOT exercise or block - radiograph first.

Osteoarthritis (Degenerative Joint Disease)

Osteoarthritis (OA) is the most common joint disease in horses, responsible for over 60% of all lameness cases. It involves progressive degradation of articular cartilage with secondary bone changes.

Common Sites and Terminology

Treatment Options

• Systemic NSAIDs: Phenylbutazone, firocoxib (Equioxx)
• Intra-articular corticosteroids: Triamcinolone, methylprednisolone (symptom modifying)
• Hyaluronic acid (HA): Intra-articular or IV (Legend)
• Polysulfated glycosaminoglycan: Adequan (IM)
• Biologics (disease modifying): IRAP, PRP, stem cells
• Surgical arthrodesis: For low-motion joints (pastern, distal hock)

Suspensory Ligament Desmitis

Suspensory desmitis is inflammation/injury to the suspensory ligament (interosseous muscle). It is classified by location: proximal, body, or branches.

Proximal Suspensory Desmitis (PSD)

• Common in sport horses (dressage, jumpers)
• Hindlimb PSD: Often bilateral; shortened cranial phase of stride; may be reluctant to back up
• Forelimb PSD: Pain on palpation over proximal metacarpus
• Diagnosis: Diagnostic analgesia (high palmar/plantar block); ultrasound; MRI is gold standard
• Treatment: Rest, controlled exercise, shock wave therapy, PRP, stem cells; fasciotomy for hindlimb cases

Diagnostic Imaging for Lameness