ANGULAR LIMB DEFORMITIES IN FOALS: What are they and how

ANGULAR LIMB DEFORMITIES IN FOALS:
What are they and how can they be corrected?
Daria L. DiGiovanni, D.V.M.
Matthew Coleridge, B.V.M.S
In Kentucky, there are thousands of foals born each year that are bred for various
purposes including sales, racing or riding. Many foals can either be born with
(congenital), or acquire a variety of mild to severe angular limb deformities. This
refers to a deviation of the limb either outward (lateral) or inward (medial) from
below a certain reference point, typically at a joint.
DEFINITION
A varus deviation refers to a horse which is typically toed-in, versus a valgus
deviation, which refers to a horse which is typically toed-out. Deviations from the
knee are the most common, followed by the fetlock and hock. Often times, more
than one limb is involved.
Congenital deviations can be due to under-developed bones and/or ligaments
such as incompletely ossified tarsal bones. Acquired deviations can be due to a
multitude of circumstances, all of which cause an unbalanced rate of growth
longitudinally. These can include nutritional imbalances, trauma, infection,
exercise, and altered loading of the limb.
Fetlock varus (toed in)
Carpus
Fetlock valgus (toed out)
Carpus
Below is an example of a foal with incomplete ossification of the tarsal bones.
TREATMENT
The treatment of the various forms of angular limb deformities differ for each
horse depending on such factors as location of the deformity, age, severity, body
type, risk factors, and time.
Conservative therapy
 Farriery and Hoof Modifications
Farriery is a simple non-invasive tool that can be used to treat angular limb
deformities in foals of less than 3 months of age.
o Trimming
 Trimming of the hoof wall on
the opposite side from which
the axis needs to move, can
achieve slight correction in
conformation. For example,
some correction could be
achieved in a varus fetlock
by trimming the inside
(medial) hoof wall.
o Hoof wall extension
 By artificially extending the hoof wall on the side that the axis
needs to be moved, this spreads the load the foot is supporting
towards the extension, thereby forcing the limb in that direction
to achieve an ideal conformation. The growth plate is effectively
compressed on the same side that the extension is placed,
slowing the growth on that side. For example, a toed-in foal
(fetlock varus) would benefit from lateral extensions placed on
the outside (lateral) hoof walls. Most commonly, products such
as Equilox, a flexible resin that can be molded by hand and then
hardens, can be used to create the extension. It is quick and
easy to perform.
 Other conservative treatments include management of the foals bodyweight,
weaning time and turnout or exercise. These modifications can reduce the
strain placed on the limb, allowing correction to be achieved naturally as the
foal develops.
Surgical therapy
 Periosteal elevation (PE)
o All bones are covered by a fibrous
layer called the periosteum. This
procedure involves making a small
incision on the concave aspect of
the relevant bone, incising the
periosteum and elevating it away
from the bone. This procedure
speeds the rate of growth on the
side of the limb which it is
performed.
 Surgical Implants
o The principle behind surgical implants placed through or across the
relevant physis (growth plate) is simple and relies on mechanical
restriction. The physis is bridged on the convex side of the deviated
limb, compressing and inhibiting the cells of the physis, thereby
arresting growth until the limb is straight, at which time the implant is
removed. There are various types of implants and techniques used to
achieve this growth arrest.
Initial techniques described a staple placed in order to bridge the
growth plate causing a tensional force, which greatly reduces growth
on the convex side of the physis. A further development was that of
two screws placed horizontally into the bone, on either side of the
growth plate and then joined with steel wire. This effectively achieves
the same effect as the staple. More recently the ‘Single Screw
Technique’ describes a screw being placed at a 60-degree angle to
the bone through the physis on the convex side of the limb. The
tension created across the growth plate by the screw retards the
growth until the deformity is corrected.
If you have questions or concerns about the conformation of your
foal’s legs, please contact your veterinarian to discuss treatment and
care.
We would like to acknowledge Dr. Michael Spirito for the use of his images and
knowledge for writing this article as well as Dr. Dwayne Rodgerson and Dr.
Robert Hunt.