What Is the Fabella in Dogs?

The fabella in dogs is a small sesamoid bone located within the lateral head of the gastrocnemius muscle, behind the knee. This evergreen explainer outlines what the fabella is, how common it is in dogs, how it is evaluated, and when it is clinically relevant. You will find concise, evidence-driven context for interpreting findings related to the fabella in veterinary practice, without speculation or sensationalism.

What Is a Sesamoid Bone and Where Is the Fabella Located

Sesamoid bones are small, round bones embedded within tendons, typically near joints, and their function is to improve mechanical advantage and reduce friction. In dogs, the fabella is a paired sesamoid found in the lateral head of the gastrocnemius muscle, sitting just caudal to the lateral femoral condyle. It is one of several sesamoids in the canine body, alongside the patella and digital sesamoids. The term “fabella” refers to its resemblance to a small bean, and it is sometimes called the lateral fabella to distinguish it from rare medial or intermediate variants.

Prevalence and Breed Observations

Radiographic and cadaveric studies indicate that the fabella is present in a substantial proportion of dogs, with prevalence estimates commonly reported in the range of 17% to 67% depending on population, breed, imaging modality, and diagnostic criteria. There is no strong evidence that the fabella consistently ossifies in all dogs, and its presence can vary by breed, age, and individual anatomy. Reported breed associations are variable and sometimes inconsistent, which limits definitive conclusions about inherited patterns. This variability is an important consideration when interpreting imaging findings in both clinical and screening contexts.

Key Reported Patterns in Breeds

• Small and toy breeds, such as Yorkshire Terriers, Pomeranians, and Chihuahuas, are commonly cited as having higher observed prevalence in some studies.
• Medium to large breeds, including Labrador Retrievers and German Shepherd Dogs, are also frequently reported with fabellar presence, though breed-specific prevalence data remain limited.
• Greyhounds and sight hounds may show variability, and some working-line populations may have different descriptive frequencies, but robust comparative prevalence data are lacking.

Clinical Relevance and Potential Issues

In most dogs, the fabella is an incidental finding on physical examination or imaging and does not cause clinical signs. Problems are uncommon but can arise if the bone is fractured, fragmented, or involved in soft tissue injury. Reported associations include gastrocnemius tears, popliteal tendon injuries, meniscal damage, and intra-articular migration of fabellar fragments, which may contribute to stifle pain or effusion. These associations are typically identified in athletic or working dogs, and confirmation of a causal relationship between fabellar pathology and lameness requires thorough orthopedic and imaging evaluation.

How Vets Evaluate the Fabella

Clinicians assess the fabella through a combination of physical examination, imaging, and, when needed, intraoperative visualization. Common modalities and their reported characteristics are summarized in the table below.

Diagnostic Imaging Tips

• Survey radiographs may miss small or poorly ossified fabellae; CT improves detection and characterization of fragments.
• Ultrasound can identify the fabella in experienced hands when it is ossified and adjacent structures are well visualized.
• MRI can help assess surrounding soft tissues when injury is suspected but is not typically required for an isolated fabellar finding.

When the Fabella Becomes a Clinical Problem

Isolated fabellar findings on imaging rarely justify intervention unless there is clear evidence of fracture, fragmentation, or migration into the joint space causing mechanical signs. When lameness, effusion, or crepitus is attributed to the fabella, a systematic orthopedic workup is warranted, including palpation, range-of-motion testing, and imaging of the stifle. If surgery is considered, the fabella may be resected or stabilized depending on the specific lesions identified. Postoperative care follows standard principles for stifle procedures, with attention to controlled activity and rehabilitation as needed.

Differences Between the Fabella and Other Sesamoids

Understanding how the fabella compares with the patella and digital sesamoids helps avoid misinterpretation. The patella is a large, intraarticular sesamoid within the quadriceps mechanism and a common site of congenital or developmental disease. Digital sesamoids are found in the distal limbs, especially in the metacarpus or metatarsus, and are relevant to foot and tendon injuries. In contrast, the fabella is smaller, located in the gastrocnemius, and usually clinically insignificant. Context, size, location, and association with trauma guide whether a sesamoid finding is an incidental fabella or a pathologic entity.

Key Takeaways for Clinicians and Owners

• The fabella is a small sesamoid bone in the lateral gastrocnemius that is commonly seen on imaging but usually not clinically relevant.
• Prevalence varies widely by study, breed, and imaging method, so reported frequencies should be interpreted cautiously.
• Clinical problems linked to the fabella are uncommon and typically involve fractures, fragment migration, or soft tissue injury nearby.
• A thorough orthopedic assessment is essential before attributing lameness to the fabella, as many other stifle conditions are more likely causes.
• Treatment, when indicated, follows standard principles for stifle trauma and may include conservative management or surgery depending on findings.

For most dogs, the fabella remains an incidental anatomical variant without impact on health or performance. Continued use of clear imaging terminology, standardized reporting, and systematic orthopedic evaluation helps ensure that clinically meaningful conditions are identified and managed appropriately.