Mysterious Limp

We haven't had an "Ask The Vet" question for a while, so here's one I just received from Laura...

I wondered if you might have some insight on what might be the problem in my little 4 yr old toy poodle.  One day, out of the blue, he started carrying his left hind leg -- almost consistently.  After a couple days he would use it to walk and trot, though it was evident that he was favoring the good leg while standing. And his posture is changed so that he holds the bad leg rather out and back from the good leg. 

Since then I have stopped walking him except to let him relieve himself.  I have allowed him to roam the house though try to keep him subdued and resting most of the time. He seems to use it a bit more since then, at least the amount of carrying is greatly reduced. He might carry the bad leg right after getting up from rest---though only rest after activity since in the morning he seems best of all, using the leg without problem. 

He never had any pain with manipulation of the leg, hip, or knee.  He can run--though I don't allow it.  He managed to do it a couple of times when I couldn't restrain him.  He stretches the leg, does the kicking out of the legs after relieving himself, can stand on his 2 back legs, can pee standing on the one bad leg, and seems to sit mostly square (though I see he leans to the good leg). 

So I have noticed that if I lift his backside up by one of his hind legs (while he is standing on his front), sort of cupping the tucked leg and lifting him from that point (so that he can , he does something different from the bad side.  I attached a picture of me lifting him up from his good side.  He will resist in the good leg and bear weight in that kneeling position.  But in the bad leg he doesn't want to bear weight. 

I have been trying out different things to locate the problem. He will bear weight in the straight position though he prefers the good leg.  But in this kneeling position he won't bear weight into that tucked knee so that I can lift his hind side off the ground.  I can feel that he won't use the muscles to resist so the knee just comes up relative to his body.  Whereas in the otherside he bears down, keeping the knee lower than his belly so that I can life his hind side.  I hope that makes sense. 

I don't know if that determines one way or another whether it COULD be the cruciate or most likely a sprain/muscular problem.  I already brought him to the vet, who determined that ít's not luxating patellas and wasn't obvious laxity in the stifle area. He didn't do a drawer test, presumeably because he just did not see it as a grave problem yet.  Also, since my dog is only 5 lbs, he is of the mind that only in the 10% worse cases of small dogs does one even operate and prefers to let them heal on their own.  So since then I decided to do the 6 weeks of restricted activity before taking him in to see an orthopedic vet. 

Have you got any suggestions or guesses as to what other problem he might be suffering?

Very puzzling question,  Laura.  My first thought in reading this is that your dog has a luxating patella, though you said the vet ruled this out.  For those reading this who don't know the medical terms, this is basically a loose kneecap.  Small dogs are very prone to this problem and it can cause intermittent to continual lameness in the hind leg without any obvious pain.  A vet can usually tell pretty quickly whether or not this is the problem, though in some cases it's difficult to manipulate the patella.  However, as severe as this sounds I would imagine that it would be pretty obvious to almost any vet.

Also for readers who don't know, a drawer test is a specific way of moving the knee to look for laxity if we suspect an anterior cruciate ligament (ACL) rupture.  This type of injury involves one of the stabilizing ligaments in the knee joint and leads to sudden lameness.  Though much more common in large, active dogs, an ACL tear can happen in any dog and I have seen smaller breeds with this kind of injury.  A positive drawer test is a strong indication that there is an ACL injury.  I'm not sure why your vet wouldn't do this test, as it doesn't usually involve sedation and is quick and easy to do with most dogs in the exam room.  Even if surgery wasn't done, you would at least know that this was the problem.  I also know orthopedic surgeons who would still do the surgery on a small dog like this.  The ruptured ligament can cause significant inflammation, which will take months to resolve without removing the damaged pieces.  There can also be tears in the meniscus (cushioning pad) of the knee, which again can cause inflammation while it remains. However, this degree of inflammation can often be felt in the knee, so your vet may have been less concerned about this particular problem.  It is true that in mild cases of ACL injury in small dogs or cats that surgery isn't necessary.  However, your dog may be in the 10% that needs it.

It doesn't sound like radiographs (x-rays) were performed, and I would recommend that as the next step.  Though I agree that it sounds more like a problem in the knee, you would also want to rule out a problem in the hip. There are certain problems that small dogs, especially poodles, are prone to, especially Legg-Calve-Perthes syndrome.  In this particular disorder, the head of the femur (upper leg bone where it connects the hip) looses blood supply and begins to deteriorate.  This problem is usually easy to detect with radiographs and requires surgery to remove the femoral head.  And while radiographs can't easily detect ligament injuries, you may be able to see changes in the knee joint that can be suggestive of an ACL injury.

Exercise restriction and pain control are certainly indicated, and may be the only treatment necessary.  However, if this was my patient I would definitely recommend the radiographs prior to waiting for that long.  If rest doesn't resolve the issue, I would certainly see a specialist and be prepared for the possibility of a CT scan or MRI to try and fully view the soft tissues in the joints.

Good luck, Laura!