The radius is the main weight-supporting bone; the ulna bone supports very little weight.
Small breed dogs have a poor blood supply to the lower fourth of the radius bone, therefore it is more susceptible to being fractured; also healing of the fracture can take longer than other bones in the body.
Surgical fixation of the fractures with plates and screws or with an external skeletal fixator is usually needed for a successful outcome.
- The fore limb has two bones between the wrist or carpus and the elbow joint: the radius and ulna bones.
- The radius is the main weight-supporting bone; the ulna bone supports very little weight.
- Small breed dogs have a poor blood supply to the lower fourth of the radius bone, therefore it is more susceptible to being fractured; also healing of the fracture can take longer than other bones in the body.
- Large breed dogs have a much better blood supply to this region, therefore a very substantial force needs to be applied to the bone before a fracture develops.
- If the radius fractures, the ulna usually fractures too.
Cause of fracture
- In small breed dogs, landing on the front limbs from a fall is the most common cause of fracture of the radius (example: dog falls out the owners arms).
- In large breed dogs, usually substantial trauma is needed, such as being hit by a car.
- Gun shot injuries will result in an open fracture; in this case dirt and hair usually are driven into the tissues and could potentially result in infection of the soft tissues and bone.
- Below is a radiograph of a fractured radius and ulna in an Italian Greyhound; she took a fall while playing with her housemate.
- The fracture is reduced and stabilized with one of the following options:
- A plate and screws are usually the best option to stabilize radial/ulnar fractures. This treatment results in the least aftercare for the client and usually has a very successful outcome. Below is a radiograph of a radial fracture repair (fracture shown above) using a plate and screws. The plate may be placed on the inner side (medial) of the radius bone or it may be placed on the top side (dorsal) of the radius bone. In the radiograph below the plate was placed on the medial aspect of the bone.
- An external fixator consists of multiple pins that penetrate the skin and bone and are connected an external bar that runs parallel to the bone. An external skeletal fixator is used:
- In some cases when an open wound is also present at the fracture site
- If there are multiple fractures of the radius bone
- A single pin placed in the marrow cavity of the bone to hold the fracture together is an old technique and is considered unacceptable, as nonhealing of the fracture frequently occurs.
- Use of a cast to stabilize the bones frequently results in a nonhealing fracture, therefore this form of treatment is considered an unacceptable option in most cases.
- Bandage is kept on for 5 to 10 days.
- In some cases a splint will also be applied to help support the internal repair
- If an external fixator has been placed, bandage changes will need to be done daily until the skin has healed around the pins.
- Check incision for signs of infection until healing has taken place.
- Exercise restriction until the fracture has healed (based on radiographs).
- Radiographs (x-rays) are taken in 8 weeks after the surgery.
- Nonhealing of the fracture
- Breakage of the surgical screws, plates or pins before healing of the fracture has occurred; this usually is associated with over activity during the healing process.
- If the pet is less than 8 months of age when the fracture occurs, angular limb deformity (bent limb) may result; this may be caused by damage to the growth plates at the ends of the bones.
Case examples of bad ways to fix radial/ulnar fractures
- Case 1: Poodle, 1.5 yrs old, spayed female
- History: dog sustained fracture after jumping out of owner’s arms, a veterinarian treated the fracture initially using a single pin
- Below is a side veiw and and front view radiographs taken 3 months after the initial surgery (arrow points to fracture in bone)
- The result was a bent, nonfunctional limb and fracture which did not heal
- To prevent such a complication, the use of a plate and screws would have been ideal
- Case 2: Domestic short haired cat, 4 years old, spayed femal
- History: cat was hit by a car and susteined fractures of the radius and ulna
- A veterinarian repaired this fracture using a single pin in the ulna and ignored repairing the radius. Because the radius is the weight-bearing bone, it is imperative that this bone stabilized with a plate, not just another pin. Cats also have excessive amount of movement of the radius and ulna (called pronation and supination), therefore it is a good idea to repair both bones. Pinning this bone does not overcome rotation at the fracture site, therefore the chance of healing is poor. This cat developed a nonunion of the fracture. Treatment again would be stabilization with a plate and screws.