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Five-year-old spayed female black Labrador retriever presented for chronic intermittent right thoracic limb lameness of 2 year duration. NSAIDS help, but do not completely resolve lameness. Radiographs were taken by the referring veterinarian 1 year prior to presentation, showing no abnormalities. Muscles of the right thoracic limb were atrophied and hyperflexion of the right carpus was suspected. On physical examination, pain of the 2nd and 3rd right metacarpal bones and 2nd digit on flexion and extension were observed, as well as pain on palpation of the right middle carpal joint and right carpometacarpal joints on flexion and extension.
Two months later, the patient returned with persistent lameness. On physical examination, severe pain was elicited on palpation of 2nd and 3rd right metacarpal bones, particularly the 3rd metacarpal bone. No soft tissue swelling was noted over the metacarpals. No pain was elicited on flexion and extension of the carpus. The carpus had normal range of motion. Muscle atrophy of the right thoracic limb was present.
Between the second and third metacarpal bones of the right manus, at the level of the mid-diaphysis, the soft tissues at the dorsal aspect contain a small (0.4 x 0.5 x 1.4cm), well-defined mass. The mass is mildly hyperintense to muscle on PD, moderately hyperintense on STIR, and is moderately enhancing. At the level of the mass, the medial cortex of the second metacarpal bone is mildly flattened.
Summary: Small focal soft tissue mass, right metacarpus, between digits 2-3
The primary differential diagnosis for the mass is a benign etiology due to the potential 2 year history of lameness, such as neuroma, fibroma or granuloma. A slow-growing malignant neoplasia is possible but considered less likely.
Soft tissue sarcoma, grade 1
The patient had reduced lameness immediately after surgery. Ten days post-operatively, the owner notes that she is moving better than she has in 2 years.
Radiographically, the smoothly margined concave defect along the medial cortex of the 3rd metacarpal bone was initially considered a normal variant. Retrospectively, this is suggestive of pressure necrosis.