The Knees Have It

This seems to be knee month. There have been lots of questions about dogs and their knee problems. This is a common problem in dogs, particularly the larger and more athletic breeds.

There are a number of ligaments involved in the knee joint, and just as in humans, they can all cause problems. The most common and troubling one is the anterior cruciate ligament, or ACL.

The ACL is one of two ligaments within the joint itself. The other one is simply the posterior cruciate ligament.

The ACL is responsible for much of the stability of the knee joint. Injuries to it are common any time the foot is planted and something hits or stresses the joint from the side. This will stretch the ligament and, in the worst case scenario, could rupture it.

The nerve supply is very sparse here, so the injury might not be more than minor at the time, but the instability of the joint is the major problem.

The dog will get used to the instability over time and it looks to the owner that it is healing, particularly if pain meds are used. But it often is not healing. As the dog continues to increase the use of the joint, the damage begins.

Over time, arthritis will begin to set in, and this is when it starts to make the dog sore and limp much more noticeably. By this time, there’s a whole new problem to deal with.

Since the ligament doesn’t show up on the average x-ray, this approach does little good to identify the problem. But an x-ray does rule out other types of injuries.

The only way to really diagnose it is by palpation, or feeling the instability of the joint.

Usually, humans can be convinced to relax while the physician plays around. It doesn’t hurt (yes, I’ve had it done to me…) but the dog usually isn’t as convinced. And in a large dog, simply tensing up will make it impossible to feel the instability.

This has to be done under a general anesthetic. It feels a bit like a drawer sliding along and is referred to as an “anterior draw sign”. Once you’ve felt this, it’s usually pretty obvious.

Once diagnosed, it’s decision time. It might be more worthwhile treating an older dog conservatively. If your pet is older, very quiet, etc. the best thing might be to simply watch it and treat the arthritis.

In a younger and more athletic animal, surgery may be the best option. But here’s where it gets more complicated.

The original surgery for this was to create an artificial ligament by drilling into both bones involved in the knee and forming a ligament to replace the broken one. This was done using Dacron or monofilament nylon.

The monofilament nylon, probably the better of the choices, is really just a high test fishing line. Some brands could withstand the heat of sterilization, and it worked just fine.

But studies showed that usually within six to ten weeks, the artificial ligament was found to break, although the surgery was a complete success.

It seems that simply keeping the knee stable for that time, and tightening the whole capsule of the knee during the surgery, did a great job. So surgeons began to just tighten the joint capsule, particularly in the small or medium size dogs. Much less invasive and it still worked the same way.

Later, some surgeons developed techniques to shave part of the knee joint off to create more favourable angles, and now some implants are being used. These techniques require specialized equipment and training and aren’t usually done by local practitioners.

The best choice is probably the technique that the surgeon is used to and does the most. Any task from painting to surgery is best done by someone who does a lot of it, so go with that.

Healing is slow and can’t be rushed. The patient has to be kept very still and quiet for six weeks or more, or the instability will return and you’re right back where you started from.

But unfortunately this isn’t the whole story. There are other factors to consider in this.

Genetics can play a part here, so this should be checked out if it’s possible.

Gait, type of work the dog does, etc. can all play a part in both the cause of the injury and the healing of it.

And you always have to think about the anatomy of the joint. Ligaments have a bit of a blood supply at each end, but the entire middle part is pretty much devoid of blood supply.

In the case of the ACL, most of its nutrition comes from the joint fluid itself, so the entire knee and the joint fluid itself are major factors.

All this leads to the disheartening fact that around 40-50 percent of animals are likely to have the ligament in the opposite knee go later. This is due to both legs having the same problems, as well as the additional strain on the “good” leg while the injured one is healing.

That’s why you have to keep the patient so quiet during the recovery period. It’s also why you always bandage the “good” leg of a horse while a leg injury heals.

But please don’t let all of this discourage you from treating knee injuries in dogs. Talk to your regular veterinarian about options. It might be the sort of question that given to 10 veterinarians, you’ll get 12 opinions.

No answer is perfectly right. Always discuss your options.

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