Equine lameness is tested on the NAVLE from two angles: the diagnostic process (grading, nerve blocks) and specific high-yield conditions (navicular, laminitis, OCD). The nerve block interpretation is the most-tested concept—understand the principle and the specific block locations cold.
AAEP Lameness Grading Scale
Diagnostic Nerve Blocks
The principle: anesthetize a specific structure or region → if lameness improves significantly (60–100%), the source of pain is in the blocked region. Always start distally and work proximally.
- Palmar digital (PD) block: desensitizes the caudal third of the foot including the navicular bone, navicular bursa, deep digital flexor tendon insertion, and caudal DIP joint. Most commonly positive in navicular syndrome.
- Abaxial sesamoid block: desensitizes the entire foot including the dorsal DIP joint. More complete than PD block alone.
- Low palmar (low 4-point) block: desensitizes the fetlock region and lower limb.
- High palmar (high 4-point) block: desensitizes structures above the fetlock including the pastern.
- Intraarticular blocks: coffin joint, fetlock joint, carpal joints—more specific to articular sources.
Navicular Syndrome (Podotrochlosis)
Degenerative condition of the navicular apparatus: distal sesamoid bone, navicular bursa, DDFT, and associated collateral ligaments. Most common in Quarter Horses and warmbloods. Signs: bilateral forelimb lameness (worse on hard ground), pointing when resting, short choppy stride, heel pain on hoof testers, positive PD nerve block.
Diagnosis: radiographs (distal sesamoid lucencies, enthesiophytes), MRI (gold standard for soft tissue). Treatment: corrective shoeing (egg bar shoes with elevated heels, breakover reduction), NSAIDs, rest, bisphosphonates (tiludronate), isoxsuprine (vasoactive drug, old treatment, evidence weak), navicular bursa corticosteroid injection.
Laminitis
Inflammation and ischemia of the sensitive lamellae (interdigitation of dermal and epidermal lamellae in the hoof capsule). Causes: grain overload, PPID, EMS/hyperinsulinemia, retained placenta, systemic illness, steroid administration.
Obel grades (acute laminitis):
Grade 1: Lameness apparent when turning; shifts weight but moves without reluctance
Grade 2: Reluctant to move; will allow foot to be picked up
Grade 3: Resists picking up of foot; moves with difficulty
Grade 4: Refuses to move; lies down
Rotation vs sinking: Rotation (coffin bone rotates within hoof capsule, tip penetrates sole) is more common. Sinking (entire coffin bone sinks distally) is more severe and carries worse prognosis.
Acute management: Deep sand/shavings bedding (support under frog), continuous icing (reduces inflammatory cascade, most effective in first 72 hours), NSAIDs (flunixin or phenylbutazone), treat underlying cause. ACEPROMAZINE IS CONTRAINDICATED—causes vasodilation and worsens digital ischemia.
OCD (Osteochondrosis Dissecans)
Failure of endochondral ossification during growth → cartilage flap formation in joints. Affects young large-breed horses (Warmbloods, Thoroughbreds, Standardbreds). Most common sites: lateral trochlear ridge of the femur (stifle), distal intermediate ridge of the tibia (hock), dorsal aspect of the sagittal ridge of MCIII (fetlock). Signs: joint effusion, intermittent lameness. Diagnosis: radiographs (osteochondral fragment), ultrasound, arthroscopy. Treatment: arthroscopic debridement and fragment removal.