Welcome to our first installment of the case of the month! We plan to use this area to demonstrate the kinds of problems we encounter in veterinary medicine, and the treatments that are available to us. These will all be actual cases seen and treated at our hospital; we'll show lab results, x-rays, and end with a discussion regarding the problem presented each month. Although the cases are real, we've changed the patients' names to protect owners' privacy.

UH-OH BREAKS A LEG

Toward the end of 1999 we saw several pets with broken bones within a relatively short time. We saw a variety of types of fractures, and different degrees of severity. Our first few cases will cover some of these.

HISTORY

Uh-oh was a young cat who spent all of his time indoors. He tended to stay out of trouble, but one night his parents came home and found him unable to walk on one of his rear legs. No one knew what might have happened, but he sometimes would climb into tight spots and something may have fallen on him or he could have gotten his leg stuck somehow.

PHYSICAL FINDINGS

When examined, Uh-oh was uncomfortable near his ankle (tarsus). There was some swelling, and he held his foot at an unusual angle. Expecting a broken bone, we took some x-rays. We normally use 2 views in order to get a three-dimensional impression of the area being x-rayed (One view of the first set in this example didn't reproduce well enough to show things clearly).

X-RAY RESULTS

Uh-oh's x-rays showed a fracture of his tibia (lower leg) close to his ankle joint. The exact area of his break was along a growth plate in the bone, which is a line of natural weakness.

Here's a close-up:

 Where the bone was broken, the normal force of the associated muscles began to pull the smaller piece of bone (along with Uh-oh's ankle joint) backwards and upward toward his knee.

TREATMENT

This fracture was fixed by placing 2 small pins into the bones across the fracture site. These pins allowed fine adjustments and very accurate positioning of the bone ends as the pins were placed. Their crossed configuration also helped ensure that the bone ends could not rotate in relation to each other during healing :

OUTCOME

Uh-oh was re-evaluated regularly as his leg healed. He had to be closely confined (which was hard!) and restricted from over-using his leg. With this fracture we planned to remove the pins after healing was completed. However, when we looked at his follow-up x-rays, one of the pins was gone already! (Because there's minimal muscle or fat in this area, the pin was just below the skin and we think he managed to pull it out somehow). We decided to leave the remaining pin in unless he shows any signs of problems later on. He's getting around great and shows no ill effects of his injury (In fact, he's been back for regular examinations and spent a few days boarding with us, and seems to have a great time!).

DISCUSSION

This section might also be called the more-than-you-really-wanted-to-know section. With this case of the month we'll briefly cover fractures, fracture repair, and fracture healing. Since we've got some other fractures to consider in the coming months, we'll leave some related topics until later.

First, what causes a broken bone? Sounds easy, but that's not always the case. In most cases, fractures result from some kind of obvious trauma (falling or being hit by a car), but in other instances something as simple as a jump off of the couch or a missed step can result in a broken bone. Very young and old animals are more susceptible to broken bones from a minor impact; pets with bone cancer are also at increased risk for fractures.

There's a specific progression of tissue changes associated with a fracture, as follows (adapted from Handbook of Small Animal Orthopedics & Fracture Treatment, 2nd edition; Wade O. Brinker et al.; 1990 W.B. Saunders Company):

  1. hemorrhage (bleeding) at the fracture site;
  2. clot formation;
  3. inflammation and edema (fluid buildup, swelling) - many inflammatory substances are produced in response to a fracture, and these along with swelling are responsible for much of the pain associated with a fracture; abnormal movement of affected bones and their associated tendons, ligaments, and muscles causes further inflammation, more pain and swelling, and in some cases more bleeding in the area;
  4. proliferation of cells - with time, inflammatory cells appear at the fracture site, in addition to cells responsible for formation of new bone;
  5. cartilage and bone formation - new bone is often called callus; initial new bone at a fracture site is rough and often doesn't conform closely to the shape of the affected bones; later, this new bone can reshape itself (remodel), sometimes so well that an old fracture isn't easy to identify:
  6. remodeling of callus back to normal bone.

You might not think of it this way, but bone is a living tissue and a surprisingly dynamic material. It's made up of a complex interaction of living cells, mineral scaffolding, and hollow channels that allow transport of nutrients and raw materials. It's able to change shape to respond to changes in the types and directions of force that are applied. In the long run, bone is actually stronger than the implants that we use to fix a fracture.

So, how long does a broken bone take to heal? The answer is, it depends. It depends on the age and health of the pet, the type and location of fracture, the length of time before repair is attempted, whether there's any infection, how active the pet is during recovery, the amount of muscle and ligament damage, the way the fracture's repaired, and more. On average, the following times apply for a fracture fixed with a pin or something similar:

Age of Animal Time for Complete Healing
< 3 months 2-3 weeks
3-6 months 4-6 weeks
6-12 months 5-8 weeks
> 1 year 7-12 weeks

Well, that's about it for this first case. We hope you found it interesting and informative, and we'll have something new for you next month!

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