What Is Your Diagnosis?

The research focused on a case study of a 12-year-old dressage-mare pony with a history of unilateral tarsal swelling and right hind limb lameness, which led to the diagnosis of septic arthritis and incidental fragmentation of the medial trochlear ridge of the talus. The pony was successfully treated with arthroscopy and antibiotics, and returned to light training six months after surgery.

Case Summary

• The pony had an initially diagnosed small laceration on the medial surface of the tarsus, leading to limping and inability to put weight on one limb.
• Radiographic and cytologic examinations showed fracture and bony fragment within the tarsus joint and high WBC count in the synovial fluid indicating septic arthritis. Normal bacterial growth was not detected in the fluid samples.
• Treatment involved arthroscopy to examine and clean the affected joint and remove the bone fragment. There was significant improvement post-operation, with the pony’s lameness reduced. Antibiotics and anti-inflammatory drugs were administered for a certain period post-surgery.
• Three years post-surgery, the mare was free of any lameness.

Radiographic Findings

• Various views of the radiographs showed a bony fragment in the plantaroproximal margin of the talus within the right tarsus. It was a 1×1 cm triangular shard, separated from the talus by a thin space.
• Soft tissues around the tarsus joint showed moderate thickening, likely due to joint inflammation caused by septic arthritis, as determined from the cytological evaluation of the synovial fluid.

Treatment and Outcome

• Arthroscopy was performed to inspect and clean the damaged joint. It revealed significant synovitis (inflammation of the synovial membrane) and fibrin accumulation inside the joint, along with a full-thickness cartilaginous defect. The bony fragment was not removed as it was deemed stable at the fracture site.
• Post-operation, the pony showed visible improvement in lameness. It was treated with a course of intravenous potassium penicillin and gentamicin, and phenylbutazone (a non-steroidal anti-inflammatory drug) for inflammation and pain relief.
• The mare was able to return to light training six months after the operation. There was no lameness seen three years post-surgery.

Discussion

• The presentation of the fracture on the talus in this pony is rare. Confirmation of such a lesion typically requires multiple orthogonal views to precisely locate the bony fragment. Other imaging methods like fluoroscopy, CT scans, MRI, and ultrasound could also provide useful data.
• The report re-emphasizes how radiographic lesions like these need a case-by-case evaluation, as the reason behind the lameness in this pony was the synovial infection rather than the fracture. Lack of lameness with such fragmentations is typically seen.
• The absence of bacterial growth in the synovial fluid culture test could have been due to false negative results. The fluid sample was not placed in a blood culture medium before the test, which can often lead to false negatives.