Q My dog was diagnosed with a cruciate ligament tear in her knee. I was told that there are two ways to fix this. One was described as a strap using “fishing leader line.”

Then I was told about a new repair that involves cutting the bone, reshaping the joint, and then putting in a metal plate to stabilize all that. I am confused.

The first repair seems almost primitive, while the second seems very involved and technically complicated. But it still seems unclear which is better and why.

Why can’t they just replace the ligament? What repair do you recommend?

A: The anterior cruciate ligament (ACL) rupture is the most common cause of hind-limb lameness in dogs. The ACL repair is, arguably, the most researched, discussed, debated and performed procedures in veterinary surgery.

Although our knowledge of the causes of ACL has improved, a complete understanding of biomechanical, genetic and environmental influences remains incomplete.

Likewise, the array of surgical techniques that are still employed indicates that we are far from the magic bullet.

The ACL is a highly specialized component of the joint. It serves to counter a defined set of forces to which the knee is subjected, and is designed to effect even distribution of forces throughout the range of motion.

Once torn, this ligament cannot be reconstructed, and we have yet to design a replacement that functions exactly as the original.

In humans, the ACL tear is most commonly the result of trauma. Presumably, absent a traumatic event, the ligament would have remained normal indefinitely.

Not so in the dog. We have come to understand that it’s the dogs individual anatomy that contributes to accelerated degeneration of the ACL. So, it’s typically something as uneventful as trotting through the yard that immediately precedes a rupture.

This is further supported by the fact that certain breeds are more commonly affected by ACL tears than others.

Labrador retrievers are one of the most commonly represented breeds, while greyhounds are virtually never seen with spontaneously occurring ACL tears.

A particular angle in the knee of the greyhound is significantly smaller than the same angle in the Labrador retriever. Physics dictate that the greater this angle, the more strain is placed on the ACL Furthermore, it appears that once a dog had demonstrated the propensity to tear one ACL, the odds of the other side going are vastly increased.

In fact, if a Lab tears one ligament, the odds are 50 percent that it will tear the other side within five months.

Even though this is the same ligament with basically the same function in humans and dogs, the repairs differ because the causes differ.

Humans tear their ACL because of an abnormal stress application. For this reason, even if the replacement structure is not as strong as the original, it will likely hold up to normal every day stresses.

In dogs, its cumulative daily stress that destroys the original ligament. So, unless we can replace it with something far stronger than the original, a direct replacement, such as a graft, is likely to quickly fail as well.

Therefore, veterinary surgeons rely on indirect means of stabilizing the knee.

The “fishing line” approach, and others like it, places a suture material in an orientation similar to the ACL to counter the major forces it originally served to restrain. The suture lies outside of the joint and away from the original ligament’s location.

The procedures that involve cutting bone are also known as dynamic procedures. The premise with these is to change the geometry of the joint in order to alter the physics of motion. Basically, the goal here is to eliminate the forces that the ACL was originally meant to oppose. The goal is not to replace the ligament but to render it unnecessary.

So, in veterinary surgery today, the repairs are of two major categories. The “fishing line” type is known as static repairs. The “bone cutting” variety is termed dynamic repairs.

Overall it appears that the dynamic repairs slightly out perform the statics in terms of long-term function and joint degeneration.

Additional benefits of the dynamic repairs are shortened recovery times and faster resolution of post-surgical pain. Most will walk on the leg two to three days after surgery. The biggest hurdle to choosing these repairs is cost. They are typically about 50 percent higher than the statics.

The static repairs provide a fairly predictable outcome. Most will achieve approximately 80 percent to 85 percent of normal function. These repairs are less expensive than dynamics. The downside is that recovery times are double that of dynamic repairs, and post-op pain is significantly worse and lasts longer.

Generally, dogs over 15 pounds will benefit from ACL surgery of either kind over doing nothing.

But all dogs will get arthritis, no matter which way you go, because the techniques are not perfect.

So, if its in the budget, I would choose the dynamic repair, which has the best outcome, the least pain and the fastest healing.

If it’s a major financial stretch, static repairs, in the right hands, offer an appropriate, economical alternative.

Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. To send questions, go to Veterinaryspecialtycare.com and click the “ask the pet docs” icon.