Download Anterior Cruciate Ligament – the ACL

Anterior Cruciate Ligament – the ACL
By Dr. Ed Mapes
Injury to the Anterior Cruciate Ligament (ACL) is the most common cause of lameness
in companion animals, and comprises the bulk of orthopedic surgeries done at our
hospital. We’ve made this diagnosis in dogs ranging from toys to working breeds, and
even in the rare feline case; but young, active, large breed dogs are the most commonly
affected.
As seen in Figure 1, the anterior cruciate pairs with the posterior cruciate ligament
inside the knee joint. Together, they assist other structures to hold the tibia in proper
alignment with the femur bone. Though both ligaments are prone to injury, damage to
the ACL is far more common.
Figure 1 a normal anterior cruciate ligament (also referred to as the cranial cruciate
ligament) is seen, along with other important structures of the knee joint. Notice the
meniscus, a pad that separates femur from tibia, which is often torn along with the ACL.
Any damage to components of this vital joint results in pain, restricted motion, and
lameness. A torn ACL allows for abnormal motion within the joint, causing bone
surfaces to degenerate, erode, and develop arthritic changes. This process continues
until the joint becomes chronically painful and the animal resorts to using only three legs
to walk (Figure 2).
Traumatic injury is usually thought to be responsible for acute clinical signs, but in fact
natural deterioration of the ligaments often contributes to ruptures in adult or senior
patients. This accounts for the presence of arthritic changes in the knee during surgery
on acutely lame animals, and explains the fact that patients sometimes rupture the ACL
in their other leg at some point after we repair the original knee.
Figure 2 arthritis is already evident in this 6-year old patient that had limped on his left
rear leg for two years. The damaged ligament allowed abnormal joint motion that led to
the arthritis; the ligament finally ruptured totally after slow deterioration. We resect
damaged material from the joint, remove arthritic bone spurs, and stabilize these knees
at surgery.
Patients brought to the hospital are commonly non weight-bearing on the affected leg.
These usually represent cases of acute ACL tears, and we can also find joint swelling,
varying degrees of pain on manipulation, and excessive motion between the major
bones.
Some cases though are partially weight-bearing – placing reduced weight on the leg –
with altered gait and pain. They have often suffered incomplete ligament tears or had
previous total ruptures and have learned to adapt to the abnormality. The lameness in
these dogs can improve over several months, but the animal never returns to full
function without recurring lameness. Over time, even a partially ruptured ACL
degenerates and eventually tears completely, leading to even more pain and abnormal
joint motion.
In the majority of cases, surgery is the only measure that can return the patient to
acceptable levels of function.
Figure 3 Jasmine is seen on her four day post-op examination. The protective bandage
will be removed today, and she’ll begin a course of range of motion exercises and
controlled leash walking as the leg heals.
Surgery to stabilize the bony structures, remove torn sections of meniscus, and debride
arthritic growths are the best chance in most patients to regain acceptable levels of limb
use and patient comfort. The pain resulting from ligament rupture is alleviated right
away, and improved stability greatly reduces future arthritis. A range of surgical
techniques are available; surgeons consider the circumstances of each case to select
the most viable surgical options.
We incorporate four treatments with the laser therapy unit after surgery as an important
aid in healing. The laser decreases swelling, pain, and inflammation and has proven to
help our patients heal faster. The first treatment is done immediately after surgery;
followed by another on the next morning. Two more sessions are scheduled within the
next week.
I make it a point to advise clients, however, that whenever a joint structure has been
damaged and we enter the capsule to make repairs, the joint will never be perfect
again. It is inevitable that, just as in human knee surgeries, the pet may experience
some discomfort after vigorous activity, and some degree of arthritic changes will occur
over time. It is unrealistic to expect complete restoration to the pre-injury joint.
We recommend joint supportive medications after surgery – canine preparations of
glucosamine, chondroitin, and methylsulfonylmethane – and weight restriction in
overweight patients as additional measures to assure success after surgery.