A description of the motion of the navicular bone during in vitro vertical loading of the equine forelimb.

This research examines the movement of the navicular bone in horse forelimbs during vertical loading to better understand its potential role in the development of navicular disease in horses.

Research Objectives and Methodology

• The study focuses on understanding the three-dimensional motion of navicular bone in horses. This bone’s movement is thought to contribute to navicular disease, a common cause of lameness in this species.
• This investigation used roentgen stereophotogrammetric analysis, a method used to measure the precise motion of bones in three dimensions. This technique allowed researchers to accurately observe and assess the movement of the navicular bone.
• The bones examined were from the forelimbs of six mature Shetland ponies. Tantalum pellets were inserted in vitro, or outside the body, to make the observations of the bone’s movement.
• The focus of these observations was under conditions of vertical loading up to 2kN, to mimic the forces experienced by the bone during a horse’s normal activities.

Results and Observations

• During in vitro vertical loading, the motion of the navicular bone and the coffin joint – the hoof’s joint – were largely limited to flexion and extension. No substantial out-of-plane motions were observed, meaning the majority of movement was front-to-back rather than side-to-side.
• The investigators noted a small amount of flexion motion between the navicular bone and the coffin bone, with this flexion correlated to the flexion of the coffin joint.
• There was significant flexion observed between the navicular bone and the short pastern – another bone in the horse’s leg – again correlated with flexion in the coffin joint.

Conclusion and Implication

• The study concludes that generally the navicular bone follows the motion of the coffin bone during flexion of the coffin joint. However, the researchers also recorded small but consistent motions between navicular and coffin bones that exist separately.
• These findings suggest that those separate movements may play a role in the development of navicular disease in horses.