Previously, vets used to lump these together, but we now know that a variety of problems may be occurring either in isolation or together, affecting the pedal bone, navicular bone, coffin joint, deep flexor tendon or navicular bursa.
MRI can detect changes in all these structures, but it is sometimes difficult to evaluate the significance of these anomalies.
Particularly interesting are horses that are lame because of pain in the navicular bone which is seen on MRI, but not on X-ray.
In a recent paper published by the Animal Health Trust, clinicians were able to monitor 22 horses with such lamenesses.
All had normal-looking navicular bones on X-ray but abnormal MRI findings.
These horses were humanely destroyed for other reasons and their feet were made available for examination.
When the navicular bones were examined under the microscope there was a very good correlation between the MRI findings and actual disease in the bone.
The examination also added weight to the suspicion that there are two distinct types of disease within the navicular bone — in some horses there were obvious problems with the cartilage on the back of the bone, while in others the primary disease had started within the spongy bone that makes up the inside of the navicular bone.
In other words, it seems that in some horses the problems start on the bony surface and work in, while in others the problems start in the centre and work out.
To read all the latest veterinary research and developments see Horse&Hound (22 November 2012)