What Is Your Diagnosis?

A Thoroughbred racehorse presenting with intermittent lameness in its right forelimb was found to have a rare type of non-articular fracture on the lateral epicondyle of the right humerus. This was diagnosed through a combination of nuclear scintigraphy, radiography, and ultrasonography.

Background

• The 3-year-old gelding was bought in for a second opinion due to intermittent lameness in the right forelimb which was especially noticeable post-training. The trainer had noted an intensity decrease, which allowed the continuation of race training. Radiography didn’t show any abnormalities, and serum tests for exertional myopathy were negative.
• During initial examination upon referral, there was mild swelling in parts of the right forelimb. Due to the ambiguous history and inconclusive radiographic evidence, full-body nuclear scintigraphy was conducted to help identify the cause of lameness.

Diagnostic Findings and Interpretation

• From the scintigraphy, an increased uptake of radiopharmaceuticals was seen in the right elbow joint, with the highest concentration on the caudodistal aspect of the right humerus. Other areas of uptake were symmetrical and considered typical for a horse of its age and use. From this, it was decided to perform radiography on the right elbow joint.
• A mineralized fragment was discovered on the caudodistal aspect of the lateral epicondyle of the right humerus via radiography. Upon ultrasound examination, it was found to be mildly displaced into the surrounding soft tissues.
• The diagnostic images led to the final diagnosis of a simple, mildly displaced, nonarticular, closed fracture of the lateral epicondyle of the right humerus, likely a partial avulsion of the ulnaris lateralis muscle.

Treatment and Outcome

• Given the lack of articular communication and the unnecessary risk of complication, surgical removal of the fragment was not recommended. Instead, a conservative approach including four months of rest and the administering of anti-inflammatory drugs was implemented.
• Upon re-evaluation after 126 days, the swelling in the right elbow joint had disappeared completely, and the horse showed no signs of lameness. Follow-up radiograph and ultrasound examinations revealed the fragment to be in the same location and stabilized by soft tissue fibrosis.

Comments

• Nuclear scintigraphy played a key role in pinpointing the injury location, leading to further investigation with radiography and ultrasonography. The diagnosis led to the understanding that, when under racing conditions, inflamed and painful movement caused by a partial avulsion of the ulnaris lateralis muscle led to lameness.
• This study highlights a unique and rare fracture in horses that may cause intermittent but marked lameness after high-intensity exercise. Veterinarians are urged to consider this fracture as a potential diagnosis and to use a combination of nuclear scintigraphy, radiography, and ultrasonography to ensure a successful diagnosis.