Fractures are a relatively common pet injury – usually the result of trauma or a fall, and a common question I get asked by owners is “Why can’t my dog’s fracture be cast?” After all, it’s commonplace in human medicine.
We often think of using casts based on our own experiences of breaking a bone. In actual fact, in dogs and cats, there are very few circumstances where a cast is appropriate, and in a lot of cases they can actually cause more damage and complications.
A much more effective form of treatment is known as surgical fixation. This is where sterile metal implants, such as plates and screws, are used to stabilise a broken bone. In the case of a broken limb, for example, there are two options for how fixation is applied. With internal fixation, plates and screws are fixed along or within a bone, underneath the skin. In external fixation, pins, bolts and screws surround the broken limb a bit like scaffolding.
Mechanisms of Healing
To understand about the reasons behind this it helps to consider the aim of bone healing, which is to allow return to full function. There are two ways bones can heal, and the way we manage fractures will impact this.
Firstly, there is primary bone healing.
This is where new bone forms uniformly between the fractured pieces and bridges the gap entirely so that the bone looks the same as before the incident. This can only be achieved when the fracture is held rigidly with no movement or strain. Have you ever noticed how a cut on your knee takes longer to heal than a cut on your shin?
The reason for this is that the skin on your knee is under constant motion and every time you walk and so the wound edges struggle to fuse together. They will of course heal eventually – just like most fractures do. The difference for a fracture that is rigidly stabilised, such as one held together with surgical implants, is that it will have little to no movement and so can heal uniformly and faster.
Secondary bone healing
In comparison, for a fracture within a cast, where the fragments of bone are able to move and rub against each other, the fracture can take longer to heal and potentially fuse in a way different to how the bone was formed beforehand. The bone may heal eventually through secondary healing (also known as ‘pathological’ healing). It may form a bony lump, or callus, as a result of excessive new bone formation in an attempt of the body to fuse the high motion fragments.
When a broken bone moves, it is also very painful. Providing good stability with internal or external fixation prevents fracture fragments rubbing and alleviates this pain. In comparison, bone fragments within a cast are often much more free to move. This can cause a lot of pain for the animal as well as being under motion, which slows the healing process.
Complications from using casts on dogs
The most severe, but also fairly common, are severe skin wounds or pressure sores. These can be concealed under the cast and go unnoticed until removed. In the most extreme cases, this can lead to amputation of the affected limb. Casts can also be big, bulky and uncomfortable so pets are less likely to bear weight on the affected leg. This leads to muscle wastage, joint stiffness and reduction in bone density.
In summary, casting is rarely the best option
When the fracture is not adequately stabilised, it can lead to increased pain and delayed healing. This is not only a worse outcome for the animal, but can also lead to more visits to the vets and the associated costs this brings. On the other hand, pets cope surprisingly well with metal implants and often begin using the limb shortly after surgery.
If you think your pet has a fracture, always seek advice from your vet in the first instance. Your vet will be able to perform x-rays to investigate the extent of the fracture and plan how best to manage it.
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