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What is Angular Limb Deformity?
Angular limb deformity (ALD) refers to a lateral (outward)
or medial (inward) deviation of a limb.
The angle point of most limb deformities is associated with a
joint. The carpus (knee joint) is, by
far, the most common joint affected.
The fetlock (ankle joint) and tarsus (hock joint) can also be
affected. More than one leg is often
involved. An angular deformity of a
limb is described by the location (joint involved) and the direction of the
angle point (inward or outward). The
terms varus (bowlegged) and valgus (knock-kneed) are used to describe the
direction of the angle point in the carpus (knee). For example, if a foal had a knock-knee angular deformity
involving the carpus, this would be referred to as a carpal valgus; if the
foal was bowlegged at the knees, this would be referred to as carpal
varus.
Angular limb deformities occur in foals of all breeds. There does not seem to be any higher
incidence of the problem in colts compared with fillies. Foals can either be born with deviated
limbs (congenital) or develop the problem later (acquired) during their first
year of life when rapid changes are occurring in the bone and joints.
Etiology
The cause of angular limb deformities is quite
complex. In general, it can be
associated with unequal (asymmetric) growth of the long bones, such as the
radius or cannon bone, of the limbs. One side of the long bone grows faster
than the opposite side. This occurs
in the growth plate near the joint resulting in deviation of the limb. This asymmetric growth may develop as a
result of abnormal weight-bearing on the limb such as with a lameness,
inflammation of the growth plate (physitis), excessive body development in
relation to bone/joint development, or injury to the growth plate. As mentioned earlier, foals may be born
with an angular deformity of a limb or limbs. This may be due to a congenitally deformed bone or bones and
ligaments of a joint too weak to maintain proper alignment of the limb. Thus the limb will deviate medially or laterally
when the foals stands.
Diagnosis
Most angular limb deformities can be diagnosed from the
clinical appearance of the limbs. However, it is very important that
radiographs be taken of the affected leg or legs. This will help the veterinarian to determine more specifically
the location of the angle point. This
is very important in determining what type of treatment is needed to correct
the deformity. The angle point is the
point where two lines intersect. The angle point is determined by first
taking radiographs from the front or back of the limb and then drawing a line
through the middle of the long axis of the bone above and below the affected
joint, on an overlay of the radiograph.
The point at which these lines intersect is the angle point. Wherever the angle point occurs is the
location of the problem. This may be
at the growth plate of the long bone, or in the joint itself. A normal appearing leg will have an angle
point of very small degrees (less than 30) or
none at all.
Sequella
Left untreated, ALD can be a crippling disorder. Lameness and eventual osteoarthritis or
degenerative joint disease can ensue.
The time of the onset of these sequella depends on the severity of the
ALD. Thus, early intervention is
important for a successful outcome.
Treatment
The type of treatment indicated for ALD depends on several
factors including the age of the foal, the joint involved, and the location
and severity (degrees) of the angle point.
It is very important that a foal with ALD be treated as soon as
possible in order to improve the chances of a successful outcome.
Stall Rest
and Diet Modification
Regardless of the severity and location of the ALD, strict
stall rest and diet modification are very important. Exercise will only aggravate and make the
problem worse. In many cases, stall
rest alone will correct the ALD. It may
require four to eight weeks of strict stall confinement with no turn
out. During this time it is very
important to consider the diet of the foal.
If he or she is being creep fed or weaned and on a concentrate,
calcium/phosphorus balance must be maintained. Otherwise, excess dietary phosphorus could result in physitis,
aggravating the ALD. Also, the amount
of concentrate fed should be reduced so the foal/weanling is not gaining an
excessive amount of body weight which
could aggravate the ALD as well.
Along with the stall rest and diet modification, corrective
hoof trimming is also important. Your
veterinarian or farrier will be able to assist with hoof care.
Limb
Casts or Splints
Limb casts or splints are required if the ALD is due to
weak ligaments and bones associated with the affected joint. A cast or splint is applied to the limb to
help support the limb and maintain it in a straight position until the
ligaments and bones mature enough to hold the weight of the foal. Usually only 10 to 14 days is
required. This type of ALD mainly
affects the carpus (knee) and tarsus (hock).
It is observed more frequently in premature foals in which the bones
of the carpus or tarsus are not completely mineralized at the time of birth.
Surgery
Severe forms of ALD require surgery. The goal of surgical intervention is to
alter the growth at the growth plate of the long bone involved. Thus, surgery is indicated to a greater
extent for ALD from asymmetric growth of the long bone physis (growth
plate). The surgical procedures used
are periosteal stripping and transection or transphyseal bridging. Periosteal stripping and transection
involves lifting the covering of the bone (periosteum) just above the growth
plate on the “short” side of the long bone.
The surgical procedure is used to enhance the growth on the side of
the long bone (such as the radius) that is slower, in hopes it will
“catch-up” with the other side. This
procedure is performed on cases of ALD of moderate severity.
Transphyseal bridging involves placing a screw in the long
bone above and below the growth plate on the “long” side of the bone and
placing a piece of stainless steel wire between them. The purpose of the screws and wire is to
slow or stop the growth on that side of the bone at the growth plate so that
the other side can catch up. It is
very important that the foal be closely monitored so that the screws and wire
can be removed as soon as correction has occurred. Otherwise overcorrection may occur.
Prognosis
In general, foals with ALD have a good outcome for future
performance if the condition is not severe, if joint damage has not occurred,
and if they are treated appropriately and in a timely fashion.
Summary
ALD in foals is correctable in most situations. The key to improving the chances of
success is early detection and treatment.
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A one-month-old Thoroughbred colt with mild and severe
carpal valgus of the left and right forelimbs, respectively. The angular limb deformity was a result of
carpal bone hypoplasia (see text) requiring casts for support.
A radiograph of a foal with mild to moderate carpal
valgus. Surgery, periosteal
transection or stripping, was performed just above (arrow) the growth plate
to enhance bone growth on that side.
Radiograph taken two months after surgery showing that
the leg has become straighter.
A radiograph of a foal with severe carpal valgus.
Implantation of screws and wires were used to stop the
growth of one side of the growth plate (arrow in radiograph above) to allow
the other side to catch up. Notice
how much straighter the leg is radiographically, six weeks after
implantation.
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