Bone bruising is a common condition often seen in young racehorses, such as Thoroughbreds or Standardbreds. It typically arises from repetitive stress, trauma, or microfractures affecting the subchondral bone, which is the layer of bone located beneath the joint’s cartilage.

Horses engaging in high-impact exercise or activities that involve sudden changes in direction or speed have an increased risk of developing this condition.

The main characteristics of bone bruising include inflammation and localized swelling, primarily in the limbs and joints. These symptoms often result in lameness and have a significant impact on the horse’s performance and overall comfort.

Horses affected by bone bruising require careful management and appropriate treatment to promote healing and minimize potential long-term consequences. Failure to address bone bruises may lead to complications such as osteoarthritis and stress fractures. [1]

If you suspect that your horse is suffering from bone bruising, it is important to seek guidance from a veterinarian. They can provide an accurate diagnosis and develop an appropriate treatment plan tailored to your horse’s specific needs.

Bone Bruising in Horses

Bone bruising in horses is also referred to as subchondral bone disease, nonadaptive bone remodeling, bone oedema, and bone contusion. [2][3][4]

This condition refers to a specific type of injury that affects the subchondral bone, which is the layer of bone just beneath the cartilage in a joint.

Intense training, racing, and other performance equine disciplines often lead to bone bruising. The repetitive forces placed on the horse’s joints in these activities can cause microfractures or subchondral bone damage.

In horses with bone bruising, the bone does not heal or repair itself in the typical manner. Instead of undergoing the normal remodeling process, where damaged bone is resorbed and replaced with new bone, the injured area shows signs of pathologic remodeling, such as increased bone density and changes in bone structure.

The term bone contusion is often used interchangeably with bone bruising and refers to the contusion-like appearance of the subchondral bone in imaging studies.

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Subchondral Bone

Subchondral bone, the layer of bone beneath the articular cartilage in joints, plays an important role in maintaining joint integrity and absorbing forces during locomotion. [4][5]

The rich blood supply to subchondral bone plays a crucial role in supporting the repair and remodeling processes of both the bone and cartilage.

During activities such as racing and training, repetitive stress placed on the joints can lead to damage and bleeding within the subchondral bone. In some cases, fluid can accumulate within the bone, which is known as bone oedema. This fluid buildup causes swelling and can contribute to pain and lameness in the affected horse.

The microdamage triggers the body’s natural remodeling response, initiating a process to restore the normal structure and function of the bone.

Bone Remodeling

Bone remodeling is a natural physiological process where damaged or old bone is replaced in response to stresses on the horse’s skeletal system. [6][7]

Osteoclasts (cells that breakdown and resorb bone) and osteoblasts (cells that form new bone) work together in the remodeling process to maintain the integrity of the bone tissue. This adaptive process enables the bone to withstand mechanical forces and retain its strength.

Osteoblasts deposit tissue in damaged areas to rebuild and prevent further damage. Following injury, it is common for weight-bearing bones, such as the third carpal bone of the leg, to become thicker and increase in density.

The process of new bone formation is relatively slower compared to bone resorption. While bone resorption can happen relatively quickly (within a few days to a few weeks), the formation of new bone takes several months.

When the rate of bone resorption exceeds the capacity of osteoblasts to keep up, an imbalance occurs, leading to inefficient remodeling. This condition is commonly known as maladaptive bone remodeling, resulting in bon