The anatomy, development and histopathology of the distal
phalanx (PIII) and the cartilages of the equine hoof were studied by
radiological and histological techniques. Chemical analyses of ash,
calcium, magnesium and phosphorus were also included.
A well defined distal palmar process was present in a 5 month
fetus. At this stage, the proximal articular surface of PIII was
still cartilaginous; its development was completed 5 months postnatally. Side bone was detectable a month later. The notch of the
palmar process may be converted into a foramen any time after 2 years
of age. Throughout development, the cartilages of the hoof were
fibro- elastic and although directly continuous with the proximal palmar
process of PIII, they were attached to the distal palmar process by a short ligament.
The side bone developed consistently in all cartilages and was invariably present from 6 months onwards. A means of classification
as short, medium, long and marked has been suggested. The short type
was the most frequent whereas the others were seldom seen in animals
under 3 years of age. The longer types were more commonly observed
in the fore than in the hind feet and some bilateral symmetry was
present. Although the presence of this bone has been claimed to be
a factor in causing lameness, this was not verified.
Bony islands were seen at different sites in the cartilaginous
plate and in the short ligament which attached the distal palmar
process to the solar border of the cartilage of the hoof; those of
the cartilaginous plate originated near to cartilage canals. A
radiological dense area was sometimes seen in the region of the palmar
process in animals older than 2 years. This was due to the presence
of the bony bridge which converted the palmar notch into a foramen.
Side bone was formed by ossification and not calcification.
Bone growth from the proximal palmar process of PIII is one of the
factors involved. Its osteogenesis was a normal process of ossification extending from the proximal palmar process of PIII. Bony islands
also occurred in the cartilage and at the level of the distal palmar
process. There was no evidence of inflammatory reaction but necrosis
and "non- provisional" calcification of the cartilage plate occurred
and became more marked with age.
There was a significant difference between the mineral composition of the side bone and that of the adjacent part of PIII. This
was related to differences in the stages of developments of the two