When a dog has a fracture, the bone begins to undergo a healing process. Fracture healing in dogs can take several weeks to months and is dependent on several factors, such as the age of the dog and severity of the fracture. But what exactly is the process of how the bone is repaired?
After a dog suffers from a broken bone, there are four distinct stages of fracture healing (as seen in the video below). These include the Inflammatory Phases 1 and 2, the Repair Phase, and the Remodeling Phase. Collectively, this process is called BONE REMODELING.
For a simpler explanation of this process, make sure to check out our blog post on Bone Remodeling in Dogs Made Simple or watch the video below.DOG FRACTURE HEALING PHASE 1: INFLAMMATION
Within hours of a fracture, the damaged area of the bone becomes inflamed. Blood flows to the fracture site, which causes redness and heat. A blood clot called a hematoma develops around the fracture site. The purpose of this blood clot is to prevent further bleeding and blood loss. Blood clotting also sets the stage to start the process of repair.DOG FRACTURE HEALING PHASE 2: INFLAMMATION
In the second part of the inflammatory phase, the immune cells take center stage as the hematoma begins to convert into a connective tissue called granulation tissue. The purpose of granulation tissue is to provide a capsule for immune cells and growth factors to enter. These specialized cells will stimulate the development of new blood vessels and bone formation in later phases.
The initial inflammatory phases lasts for 3-4 days and potentially longer, depending on the degree of fracture. Once these phases have taken place, the broken bone can now begin to form a callus.DOG FRACTURE HEALING PHASE 3: REPAIR
After the reactive stage, the granulation tissue on the fracture site is ready to move into callus formation. The purpose of the repair phase is to provide a temporary splint to join broken ends together. Callus formation has two parts - soft callus formation and hard callus formation.
SOFT CALLUS FORMATION. Soft callus (made mostly of collagen) is created around the fracture by a group of cells called chondroblasts. During this time, there are also specialized bone cells in a dog’s body that are working called osteoblasts and osteoclasts. Osteoclasts break down bone - they eat away at the old bone, creating a cavity. Osteoblasts are bone-forming cells. They secrete osteoid, an unmineralized organic matrix.
HARD CALLUS FORMATION. In the second stage of the repair phase, the soft callus is mineralized by osteoblasts into a hard callus, called woven bone. Hard callus bridges the new bone to existing bone.
During fracture healing, progression from soft to hard callus depends upon an adequate blood supply and a gradual increase in stability at the fracture site. The balanced action of osteoclastic resorption and osteoblastic deposition is promoted by bio-replenishments (i.e. lactoferrin and R-ELF), bone vitamins and minerals.
At the end of the repair phase, bone union is achieved, but the structure of the fracture site differs from that of the original bone. This type of bone is called woven bone; it is comprised of a randomized organization of collagen fibers and is mechanically weak. It is important to keep your dog immobilized as much as possible because hard callus lacks the strength and rigidity of the original bone.
At the end of the repair phase, the injured bone will have regained enough strength and rigidity to allow low impact exercise.DOG FRACTURE HEALING PHASE 4: REMODELING
Fracture healing is completed during the remodeling stage in which the healing bone (if set properly through a splint, cast, or other structural support) is restored to its original shape, structure, and mechanical strength. During this final phase, the large callus is reduced to the size of actual bone at the fracture site. The woven/primary bone is replaced with secondary lamellar bone.
This final mineralization process can take weeks, months, or even up to a year.LENGTH OF TIME FOR A BROKEN BONE OR FRACTURE TO RECOVER IN DOGS
The time required to achieve complete union and mineralization varies based on the severity and location of the fracture. The status of the adjacent soft tissues and patient characteristics such as breed, age, health status, concurrent injuries/diseases also influence the rate of healing.
PUPPIES. Broken bone healing time in puppies is relatively short - about 2 to 4 weeks. Younger dogs have more bone building cells (osteoblasts) because they are growing, so their bones are constantly remodeling anyway. This time frame can of course differ based on the severity of the fracture and condition.
ADULT DOGS. For adult and senior dogs, broken bone healing time is usually between 6 to 12 weeks. This length of time can be more depending on the nature of the fracture. The chart below shows some of the average healing times associated with fractures in dogs.
You can read more about bone remodeling by visiting our blog The Bone Remodeling Process in Dogs Made Simple.FACTORS THAT INFLUENCE THE RATE OF BONE HEALING
Just as there are many factors that can influence your dog's bone healing, there are also many factors that can delay bone healing that should be taken into consideration, such as:
Age. An older dog takes longer to heal (about 12 weeks or more) where as a growing puppy may heal in as little as 5 weeks.
Lack of Exercise Prior to Injury. Moderate exercise helps maintain muscle mass and preserve joint flexibilty.
Obesity. Weight can place stress and strain on the bones and joints. This can cause a delay in the ability of the fracture to heal.
Poor Nutrition. New bones require mineralization. If a dog is lacking in a nutritious diet he or she may miss out on vital nutrients that promote bone remodeling.
Severity. The severity of the fracture affects the formation of blood clotting around the fracture site and can delay the formation of repair tissue.
Pre-existing Conditions. Joint disorders, cartilage deterioration, nutrient deficiencies, previous surgeries, even genetic pre-disposition can delay or affect the rate of healing.
Infection. Whenever the bone is exposed there is always the risk of bacterial contamination and infection. This can delay union. Antibiotics can help to combat infection, but many bacteria are resistant and can still thrive.
Excessive Movement. Movement at the fracture site causes a delay in healing due to a non-union of the bone ends.
Delayed Visit to Your Vet. Your vet can check to make sure your dog doesn't have any infections. They can review x-rays to make sure the broken bone is healing properly. Your vet can also perform surgery to remove any broken fragments and apply a proper cast.FURTHER READING ABOUT FRACTURES AND BONE HEALTH
Curious whether your dog has a broken leg? Make sure to look for signs and symptoms in our blog Six Ways to Spot Your Dog's Broken Leg.
For a dog that has just been brought home from the veterinarian with a broken leg, check out our guide on Broken Leg Recovery in Dogs (which applies to all broken bones).
This content is written by our Clinical Advisory Board for informational purposes only. It should not be viewed as an endorsement for any product or as a substitute for the advice of your veterinarian.