The effect of bilateral palmar digital nerve analgesia on the compressive force experienced by the navicular bone in horses with navicular disease.
Authors: McGuigan M P, Wilson A M
Journal: Equine veterinary journal
Summary
# Editorial Summary: McGuigan & Wilson (2001) Navicular disease in horses involves increased compressive loading on the navicular bone during early stance, but whether this represents a primary pathology or a pain-avoidance response has remained unclear. McGuigan and Wilson investigated this distinction by performing force plate and kinematic analysis on seven horses with confirmed navicular disease (clinical signs, radiographic and scintigraphic evidence), measuring compressive forces before and after bilateral palmar digital nerve blocks to desensitise the heel region. Following nerve analgesia, compressive forces on the navicular bone decreased significantly throughout stance phase: peak force at the beginning of stance dropped from 7.05±1.10 N/kg to 6.46±1.15 N/kg (P = 0.01), and at the end of stance from 5.00±2.05 N/kg to 4.39±1.65 N/kg (P = 0.05). The authors propose that horses experiencing heel pain—whether from the heel structures themselves or the navicular region—reflexively contract the deep digital flexor muscle to offload the heels, paradoxically increasing compressive load on the navicular bone; sustained mechanical stress then drives bone remodelling and potential flexor cartilage damage, perpetuating the disease cycle. This framework suggests navicular disease may represent a end-stage consequence of various heel-related pain sources rather than a discrete primary condition, with significant implications for diagnostic interpretation and early intervention strategies in heel lameness.
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Practical Takeaways
- •Pain in the heel region causes horses to shift loading patterns in ways that increase stress on the navicular bone, potentially creating a pain cycle that perpetuates navicular disease
- •Early identification and treatment of heel pain may prevent the biomechanical changes that lead to navicular bone remodelling and cartilage damage
- •Navicular disease management should consider the underlying heel pain that may have initiated the condition, not just treat the navicular bone itself
Key Findings
- •Peak compressive force on the navicular bone decreased from 7.05±1.10 N/kg to 6.46±1.15 N/kg at early stance after palmar digital nerve block (P=0.01)
- •Peak compressive force decreased from 5.00±2.05 N/kg to 4.39±1.65 N/kg at late stance after analgesia (P=0.05)
- •Horses with heel pain respond by contracting the deep digital flexor muscle to unload heels, which paradoxically increases navicular bone compressive load
- •Navicular disease may represent an endpoint of various heel-related conditions triggered by altered biomechanics in response to pain