What is sidebone?
Sidebone is a name for a condition that results from ossification of the
collateral cartilages of the foot. The collateral cartilages are found
on the medial (inside) and lateral (outside) aspects of the foot and can
be palpated just above the level of the coronary band, as flexible projections
on each side of the lower pastern. They are normally important as
shock-absorbers for the foot. Because cartilages are normally elastic,
they allow the foot to deform during weight bearing, and then return to
its previous shape. When they are ossified (become sidebone) the cartilages
transform into much harder and less flexible structures.
Sidebone develop more commonly in the front rather than the hind feet
and are more frequently seen in the heavy (draft) breeds of horses than
the lighter breeds and ponies.
What causes sidebone to develop?
Ossification, starting at the junction of the collateral cartilages with
the pedal bone (P3 or distal phalanx) is believed to be part of most horse's
normal ageing processes. Mild sidebone formation, not associated
with lameness, is not uncommonly seen in radiographs (x-rays) taken from
older horses and young draft horses. Excessive, abnormal or premature
sidebone formation, i.e. the promotion of transformation into bone may
result from undue loading and concussion of the cartilages, which may
be predisposed by a number of things:-
- poor foot conformation, especially chronic imbalance, associated with
incorrect hoof trimming and/or shoeing.
- foot lameness from whatever cause, particularly if this is due to
- abnormal limb conformation may cause uneven forces on the collateral
- direct trauma to the collateral cartilages may also precipitate sidebone
How is sidebone diagnosed?
Sidebone may be palpable above the coronet, when there is loss of normal
pliability of the heel over the cartilage. The coronary band may
bulge over the affected cartilage and the adjacent hoof wall may becomes
more upright in conformation.
Lameness, primarily associated with sidebone, is rarely
seen and if lameness occurs it is usually caused by complicating features,
e.g. when the ossification becomes advanced and the growing sidebone press
on adjacent sensitive hoof structures and deform the foot. Sidebone
may however secondarily contribute to lameness in the lower limb due to
the lack of shock absorption that occurs following their development.
Ossification of the cartilages is confirmed by x-ray examination of the
foot (normal cartilage cannot be seen, whereas bony ones can), comparing
one foot with another, to aid interpretation (see the attached x-ray).
The use of MRI can determine the significance of sidebone better than
How can sidebones be treated?
Uncomplicated, normal, progressive ossification of the sound horse’s
collateral cartilages causes no clinical problems and requires no treatment.
Where clinical problems occur, most importantly lameness, it is most important
to identify and treat the complicating or predisposing problems:-
- Foot imbalance should be corrected by skilled trimming and shoeing
- Fit a flat, wide-webbed shoe, with a rolled toe, wide at the quarters
and heels and extending beyond the ground surface at the heels, to support
the heel and encourage expansion. No nails should be used behind
- The horse should have an extended period of rest (6-8 weeks).
- A course of non-steroidal anti-inflammatory medication (typically
bute) if the condition is causing lameness.
- The affected foot should be re-shod regularly to gradually encourage
How can sidebones be prevented?
Your horse’s feet should be regularly trimmed and shod to prevent
imbalance, uneven weight-bearing and to ameliorate concussive forces in
The prognosis for complete resolution and return to soundness is poor
for cases where sidebone are causing lameness, especially those with extensive
cartilage ossification and hoof deformity.
So called 'fractured' sidebone, sometimes seen at radiographic (x-ray)
examinations, are usually separate centres of ossification (bone formation),
where disorganised transformation from cartilage to bone has created 'islands'
of bone within the collateral cartilage, giving the impression of a fracture
on the x-ray film. Very, very rarely there can truly be a fracture
to a large ossified sidebone.
If your horse is lame, all other causes should be excluded before sidebone
The material contained in this website is presented for information purposes
only . The material is in no way intended to replace professional veterinary
care or attention from a professional veterinary surgeon.
The advice given in any of our web pages cannot be used as the basis
for a diagnosis or choice of treatment.
Clyde Vet Group advises that you should always consult a veterinary surgeon
about any queries with animals under your care.