The Anterior Cruciate Ligament Rupture

by Christopher Forsythe, DVM

One minute your dog is bounding gracefully across a field in pursuit of a rabbit,
a butterfly, or a blowing leaf, and the next minute he is hobbling back, three-legged lame. In between, you hear the horrendous sound of a dog yelping in pain. The sound of the yelp, reportedly, is atrocious, a wretched high-pitched scream something akin to what Michael Jackson would emit if somebody removed his children’s face masks in public. With the dog’s rear leg limp as a chimp gone gimp it is time to head to the vet who will likely diagnose a ruptured ACL (anterior cruciate ligament) and let you know that your pet will need surgery to fix it.

Traumatic or degenerative injury to the anterior cruciate ligament results in partial to complete instability of the stifle or “knee” joint of the dog. ACL degeneration happens in all breeds of dogs, most commonly in those over five years old, but we also see it in young large breed dogs, like Rottweilers and Labrador Retrievers.

The function of the cruciate ligament is to stabilize the knee so the lower leg won’t rotate around or slip out with respect to the upper part of the leg. Most of us have heard about the myriad of skiers who have blown out their ACL, but I speak from experience when I say you don’t have to be Suzie Chapstick snowplowing the Alps to have this happen. From Schnauzers to Mastiffs and all those in between, dogs are quite capable of easily blasting out this most necessary and taken-for-granted part of their anatomy. Most of the time, dogs rupture the ligament by hyper-extending their leg and rotating it at the same time (for instance by running forward and stepping into a gopher hole). But for some pets, our senior citizen Labs for instance, simply hopping off a sofa has resulted in that yelp
followed by the three-legged stance.

Not exactly rocket science

The simplest way to confirm ACL rupture is to demonstrate cranial drawer motion, which is when the doctor stabilizes the pet’s knee with one hand then pulls the shin forward like he is trying to open a “bureau drawer” slightly. If the ligament is completely ruptured, there is a laxity in the joint, and the tibia moves forward slightly. If there is damage to the meniscus (the little pad in the stifle), the doctor often hears clicking during this palpation. Sometimes pets make this diagnosis more challenging by using their muscles to resist the palpation due to pain and fear. And who can really blame them? After all, with all this talk about drawer movement, you’d almost think we were talking about old Aunt Mavis’s best beechwood dresser, not the precious family pet.

X-rays, although rarely diagnostic for rupture, are very helpful in confirming joint disease. Some common radiographic findings are fluid in the joint and a pressing on the fat that normally sits invisibly in the joint. This “fat pad” is confirmation of swelling and inflammation inside the knee that results from the torn ligament and subsequent disease inside the joint.

Oh no, I got to go under the what?

That’s right, an ACL correction requires surgery in virtually every case. Surgery speeds the rate recovery, prevents degenerative problems, and is really the only way to return your frolicking pooch to his normal self. Some veterinarians offer to let clients with very small dogs, those lightweights about seven pounds and under, the chance to heal on their own. About 15 percent of these powder-puffed pooches actually improve or return to normal within six months.

Common surgical options include Tibia Plateau Leveling Osteotomy (TPLO) and extracapsular techniques. TPLO involves changing the angle of the tibia by cutting the bone to adjust the angle of thrust. Once the forces are altered, the drawer movement is corrected and the pet can move without trouble. This technique works well in very large breeds and has a quick post surgical recovery time.

Extracapsular repair is involves placing large sutures in a figure eight pattern around the joint to replace the stabilizing forces lost by the broken ligament. While recovery time is a little longer than with the TPLO, the success rate is still very good, and the price tag for this procedure is generally much lower.

It’s a bird, it’s a plane, no…it’s Sealy!

When the pet sitter came in with Sealy, she needed a drink more than Sealy needed a physical exam. The poor woman had been pet sitting only a few days and never expected the sweet, aging German Shorthaired Pointer to blow out her knee. But Sealy is a force to be reckoned with, and she loves all life, be it flowers, butterflies, or the horses in her field. On this particular day, she was harmlessly darting around when something unexpected gave way in her back leg.

She came back to her pet sitter three-legged lame and looking totally bewitched, bothered and bewildered, but not nearly as befuddled as her nanny did when I broke the news. “ACL rupture.” As I showed her the X-ray and began to talk about surgery I could see her face blanch. At least some of the color returned when I told her, “You did nothing wrong; this could have happened if Sealy just walked across the yard.”

Fortunately, Sealy has a caring mom who came back to town quickly and allowed us to do surgery in short order. We performed the extra-articular technique and were able to stabilize her leg and correct the deficit. With a morphine patch to relieve pain post operatively, the metronome movement of her nubby tail was back in full swing, and the glimmer had returned to her eyes.

Is this forever and ever?

The good news is that your pet’s rebuilt stifle will likely last for many years to come. The knee will probably withstand more force than poor Nancy Kerrigan’s after being pummeled by Tanya Harding and her chubby bodyguard. The bad news is that about 50 percent of the time the cruciate in the opposite knee will go out within six months to a year. This is particularly true for pets who have degenerative changes and are senior patients. So it is important to be prepared for this possibility should you hear that dreadful yelp and hear an unmistakable bark that seems to be saying “Why me? Why me?”