- 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.
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The fore limb has two bones between the wrist or carpus and the elbow joint called the radius and ulna bones. The radius is the main weight-supporting bone; the ulna bone support amount of weight. Small breed dogs have a poor blood supply to the lower fourth of the radius bone, therefore it are more susceptible to being fractured. Small breed dogs also may have slow bone healing of the fracture. 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. When the radius bone 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. This results in dirt and hair being driven into the tissues and can result in infection of the soft tissues and bone.
Preparation for surgery
Your pet should be fasted prior to surgery, as instructed by the surgical team. Water is usually permitted up to the time of admission to our hospital. You should inform the surgical team of any medications that your pet is currently receiving and of any pertinent medical alerts (allergies, seizures, drug insensitivities, etc). Just prior to surgery, your pet will receive a sedative, have an intravenous catheter placed for the administration of intravenous fluids and intravenous medications, be induced under general anesthesia with medication(s), and have a breathing tube (endotracheal tube) placed to allow delivery of oxygen and gaseous anesthesia. The surgical site will be clipped and cleansed with an anti-septic solution in preparation for surgery. While under general anesthesia, your pet’s breathing will be assisted with a ventilator and vital parameters such as heart rate, respiratory rate, core body temperature, blood pressure, oxygenation of the blood (pulse oximetry), exhaled/inhaled carbon dioxide (capnography), and heart rhythm (EKG) will be monitored to ensure the pet’s well being. Pain will be controlled both during and after surgery with analgesics (pain-controlling medication). Please note that each surgical and anesthesia team may elect to choose a different, but effective analgesia protocol, pending the needs of the patient.
The best option to stabilize radial/ulnar fractures is with a bone plate and series of screws. This treatment results in the least aftercare for the client and usually has a successful outcome. 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. Because the ulna bone does not provide must load sharing, it usually is not repaired with a metal plate. Below are illustrations showing, the radius/ulnar fractures, a front view with a bone plate applied to the bone and a side view showing the bone plate and screws.
In larger dogs in which there is comminution (multiple pieces), the ulna bone may also require stabilization with a plate and screws.
In some cases the fracture can be done as a minimally invasive procedure with a relatively small incision made at the top and at the bottom of the radius bone. A bone plate is slid over the bone and then secured with 2 or 3 screws at each end of the bone. Minimally invasive bone fracture repair usually results in quicker bone healing.
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 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.
A bandage is kept on for 5 to 10 days after surgery in most cases. In some cases, a splint or cast will also be applied to protect the internal surgical repair during the bone healing phase. If an external fixator has been placed, dressing changes will need to be completed daily until the skin has healed around the pins. The incision should be checked for signs of infection until healing has taken place. Exercise must be restricted until the fracture has healed (based on radiographs). Radiographs (x-rays) are taken in 8 weeks after the surgery. However, if the patient is only a few months of age, radiographs may be made earlier, as bone healing occurs quicker.
Complications may include, Infection, nonhealing of the fracture, breakage of the surgical screws, plates or pins before healing of the fracture has occurred. Catastrophic implant failure is usually is associated with over activity during the healing process.
If the pet is 4 or 5 months of age when the fracture occurs and the growth plate has been concurrently damaged due to the accident, angular limb deformity (bent limb) may develop. This would require a secondary surgery to straighten the limb out.
Most patients will have uneventful healing of the fractures within 8 weeks after surgery. In some cases, the ulna bone does not heal together or may partially resorb in the area of the fracture, however, that does not seem to affect the clinical outcome, as this bone is not the major weight-bearing bone.
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 splint. Below is a side view and and front view radiographs taken 3 months of splinting (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 the treatment of choice.
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. Best treatment again would be stabilization with a plate and screws.