The biomechanics of what really causes navicular disease.

This study explores the conflicting theories about the origins of navicular disease in horses and presents new findings about how horses contract and deal with the disease. The research suggests that the disease might be triggered by abnormal biomechanical forces on the horse’s foot, leading to tissue degeneration and pain.

Background

• The research focuses on navicular disease in horses, a complex and often difficult-to-diagnose condition that causes heel pain and can interfere with performance.
• Historically, the main theories about the causes of navicular disease have revolved around vascular compromise (which has lost credibility) and biomechanical issues leading to tissue failure.
• Abnormal forces on a horse’s navicular bone could result from either excessive loads on a normally-formed foot or normal loads on a poorly-formed foot. This usually leads to a symptom known as a “broken-back foot pastern axis”.
• Previous studies have associated abnormal biomechanical forces with degenerative changes in the navicular bone, similar to effects seen in osteoarthritic joints in humans.

Recent Findings

• The researchers found that horses with navicular disease often adjust their gait to unload their heels early in their stance phase.
• This results in excessive stress and force being placed on the navicular bone early in the stance phase and causing additional morphological changes. This was contrary to the initial hypothesis, which assumed an increased stress later in the stance.
• The study also noted that injectable pain relief (analgesia) led to a decrease of the compressive force in the stance phase. However, the analgesia didn’t return the bone force curve to that of healthy horses, suggesting that the remodeling of the bone structure due to the disease isn’t completely reversible.

Implications and Further Research

• Future research will need to determine the causes of initial pain that triggers changes in gait to relieve pressure on the heels, as well as explore why horses with navicular disease increase load on the navicular bone as a compensation.
• There’s also a need for more understanding about the site in the horse’s foot — known as an intersection — where the disease possibly initiates. This site is rich in sensory innervation, which could be instrumental in regulating forces exerted on the foot.