Suspensory Ligaments and
Degenerative Disease
by Julie Cary, DVM, MS
Diplomate, American College of Veterinary Surgeons
Associate, Cave Creek Equine Surgical Center
One form of lameness associated with suspensory ligaments
is
Degenerative Suspensory Ligament Disease (DSLD) and is a point of
frustration within the veterinary community, both because of lack of
great treatment options and because very little is understood
today about what triggers the process, or how to avoid or slow the
degeneration. Interestingly, some horses degenerate with
very little associated pain, while others will experience such
pain that euthanasia will be considered as a reasonable option.
What is the Suspensory Ligament?
The suspensory ligament runs along the back
of the cannon bone attaching the top of the cannon bone to the
sesamoid bones at the fetlock joint. Along with the distal
sesamoidean ligaments, the suspensory ligament forms the sling that
supports the fetlock. The name of the ligament reflects the
“suspension” of the fetlock. The anatomically correct name for the
suspensory ligament is the third interosseous muscle, which reflects
the presence of muscle fibers within the ligament.
What causes lameness in the Suspensory
Ligament?
There are several types of injuries that can happen to the
suspensory ligament. It is like any other tendon or ligament, which
can get stretched beyond its capacity, causing tearing of the
fibers, swelling within the structure, resulting in the classic
“bow”. During times of overextension of the fetlock, small pieces of
bone at the attachments of the suspensory ligament may be torn loose
of the bone. These are known as avulsion fractures. There is also a
class disease that results in the breakdown of the suspensory
ligament without a traumatic or overuse origin including a condition
known as degenerative suspensory ligament disease.
What is DSLD?
Degenerative suspensory ligament disease (DSLD)
refers to cases that have seemingly spontaneous loss of the elastic
property of the ligament. This loss of elasticity results in a
gradual stretching of the ligament, which is seen as an increase in
extension of the fetlock (it comes closer to the ground). The
resulting conformation is a straight hock and fetlock that is at a
more severe angle with times where the pastern bones are almost
parallel with the ground. It is unknown if the conformation of the
horse originally (ie, straight hocked) contributes to development of
breakdown to the hindlimb suspensory. It is almost always seen in
both hindlimbs, although one hindlimb may progress faster than the
other.
There is some indication that this disease
may follow family lines in certain breeds, such as Peruvian Pasos.
Also, pregnant mares in the last part of their pregnancy seem to
have an increased chance of having the painful form of this
degeneration. It is suspected that this may be due to hormonal
levels. These horses are often hospitalized and relatively heroic
measures are taken in some cases to get the mare to term in order to
save the foal.
How is DSLD diagnosed?
Diagnosis of DSLD can be challenging when
the process is in the initial stages. Horses are often positive to
both upper and lower limb flexion with fairly exaggerated lameness
occurring. Clinical judgment combined with the results of the
flexions, diagnostic nerve blocks and imaging such as radiographs
and ultrasound generally lead the veterinarian to the diagnosis of
degenerative suspensory ligament disease. Blocking the lameness can
be frustrating, as it often requires a couple of different blocks to
relieve the lameness entirely. Radiographs can reveal displacement
of the sesamoid bones. Ultrasound can be an indicator of the amount
of damage to the ligament. Ultrasound of the suspensory ligament of
the hindlimbs can be challenging in some cases because the splint
bones can interfere with the image. Use of the MRI in the future
will help further characterize the damage to the ligament.
How is DSLD treated?
Treatment considerations include shoeing changes to decrease
pressure on the suspensory ligament. Pain control if required may
include herbal remedies, phenylbutazone, acupuncture, or more potent
medications such as epidural morphine, depending on the level of
discomfort. It is important to avoid excess body weight in these
cases, as that causes more pressure on the suspensory ligament.
Currently, many practitioners are included the use of Omega fatty
acids in their treatment regimes to decrease inflammatory effects.
Exceedingly painful cases, such as occurs with pregnant brood mares
may require more heroic efforts such as body sling support and
epidural medications. The ultimate goal, at this time, is to provide
comfort for the horse and to slow the progression of the
degeneration. With time and further research, veterinarians may
ultimately learn to more effectively avoid and treat the condition.
