Fractures in dogs and cats are most often caused by trauma, such as being hit by a car or jumping or falling from a height. Fractures can also be caused by aggressive cancer that destroys the bone or by certain metabolic conditions that leach calcium from bone.
Bones provide a rigid structure to the body and act as the levers that turn muscle movement into motion [link to dog and cat skeletons]. The term “bone” makes most people think of the bones in the limbs, such as the femur (thigh), tibia (shin), radius (forearm), and humerus (upper arm). However, the ribs, spinal vertebrae, hips, shoulder, and skull are also made of bone. In dogs and cats, the spinal vertebrae extend all the way down into the tip of the tail. Male dogs also have a bone in the penis.
Bones consist of an outer, hard portion known as the cortex and an inner, spongy portion known as the marrow. The outside surface of the cortex is surrounded by a fibrous capsule called the periosteum, which contains blood vessels and nerves [link to cross-sectional diagram of bone]. The periosteum also contains immature cells that grow into the osteoblasts, which are the cells involved in growth of bone and fracture repair.
In young animals, plates or layers of osteoblasts are found near the ends of bones, from which new bone grows as the animal matures. Damage to these developing plates can stunt bone growth and lead to deformed limbs.
Bones contain large amounts of calcium, which makes them hard and resilient, but unfortunately also breakable. The complexity and severity of a fracture depends on the force of the impact, the location of the injury, and the general age and health of the individual dog or cat [link to sketches of the different types of fractures].
Hairline fractures: The simplest types of fractures produce fine cracks near the middle of long bones, such as those in the legs. These hairline fractures cause little or no displacement of the bone, much like cracks in a windshield.
Multiple-piece fractures and fractures that involve a joint: Stronger impacts can cause the edges of the fractured pieces of the bone to separate, or the bone may shatter into multiple pieces, making repair more difficult. Fractures that involve a joint are even more serious. These types of fractures can interfere with movement and lead to arthritis long after the bone has healed.
Open or compound fractures: Fractures in which the bone is exposed are called “open” or “compound” factures. In these serious fractures, jagged edges of the bone can pierce surrounding tissues and damage muscles, blood vessels, and nerves. In addition, because the bone is exposed to the outside environment, these types of fractures are often contaminated and serious infections that are difficult to resolve can develop.
Transporting your pet to Gandy Animal Hospital, Inc.
If you suspect your pet has a fracture, try to minimize movement of the affected leg while you transport your pet to your veterinarian. If any of the bone is exposed, cover it with a damp, clean towel to protect the area. Damage to the periosteum caused by the fracture is very painful, so take care while moving your pet—any animal may bite when in pain or frightened.
Your vet will begin evaluating the fracture and perform a complete physical examination to check for any additional injuries. X-rays will be needed to assess the fracture more thoroughly and to consider how best to stabilize and repair it.
Depending on the specific nature of the fracture, your vet may recommend external stabilization or internal fixation. The objective of all procedures is to bring the pieces of bone into the correct alignment and to hold them firmly in place (ie, no movement) so that healing can occur.
External stabilization consists of traditional splints, casts, and padded bandages that can be used to immobilize minor or simple fractures (eg, hairline fractures). Internal fixation involves surgical procedures to piece the fracture together while your pet is under anesthesia. The simplest type of internal fixation consists of inserting a metal pin lengthwise into the center of the bone, so that the pin can act as an internal splint. This type of internal fixation can work well for a small pet that has a simple fracture in the middle of a long bone, such as the femur, or thigh bone. In fractures that have multiple bone pieces or involve a joint, internal fixation is more complicated; the pieces need to be replaced manually and held in place with metal plates, pins, screws, and/or wire. Because this type of surgery requires specialized skills, your vet may refer you to an orthopedic specialist.
Healing and recovery
Fractures heal from the outside in. Blood vessels in the periosteum produce a fibrous capsule called a callus. The callus surrounds the outside of the fracture to hold the damaged bone in place while it heals. Specialized cells called osteoblasts then enter the fracture site to produce new bone that toughens the mend.
Healing occurs at varying rates depending on the age of the pet, the type of fracture and severity of the damage, and the type of fixation.
For example, young puppies generally heal within a few weeks, while healing can take several months in older dogs. It is important to limit your pet’s activity during the healing process, so that the bones stay aligned and heal together properly. Too much activity can refracture the bone, delay healing, or lead to a deformed limb from stress on the weakened bone. While your pet is convalescing, your vet may recommend x-rays at various time intervals to gauge how healing is progressing and when your pet can return to full function.