A 7-year-old male neutered large breed dog presented with a history of limping on the right forelimb over approximately 6 weeks. The owners thought the limping started after falling during vigorous play at the park. There was initial improvement after a course of non-steroidal anti-inflammatory medication. However, the lameness flared up a number of weeks later after a jump off the lounge.
Further examination by the local veterinarian isolated pain with manipulation of the carpus. The course of NSAIDs was extended but the lameness persisted, so the patient was referred to North Shore Veterinary Specialist Hospital (NSVH). The carpus was the consistent site of reaction with manipulation, particularly flexion. There was no visible swelling or reaction to palpation along the bones. Since the lameness appeared to have started acutely with vigorous play and a stumble, and there was no observable swelling, a soft tissue injury to the supporting ligaments of the carpus was the main initial differential diagnosis.
Carpal instability can be assessed with stressed radiographs, but unless the injury is relatively severe and the joint grossly unstable, the interpretation can be subjective and not definitive. Therefore, an MRI scan for this patient case was regarded as the most appropriate examination even though MRI is not traditionally used to image the carpus in the veterinary world. Multiple sequences were performed using a 1.5T MRI scanner. This was reviewed by a Specialist Radiologist and clearly identified a mass in the distal radial metaphysis, unfortunately consistent with a primary bone tumour (Figures 1.1, 1.3,1.4).
Although the initial focus of the MRI was for assessing the soft tissue structures, it also provided detailed information about the affected bone. There was marked interruption of the radial cortex around the caudolateral aspect of the distal metaphysis (Figure 1.2), interpreted as representing a pathological fracture within the bone associated with this expansile mass. This would explain the pain with flexion of the carpus and episodic exacerbation during exercise or stress. The tumour had not significantly expanded dorsally, so there was no swelling or pain on palpation appreciated on the initial physical examination.
Sadly, primary bone tumours are associated with a poor prognosis. The owners elected to return to the regular vet for staging and amputation.
Case study credit: Dr Craig Bailey (Surgical Specialist) and Susan Proctor (Specialist Radiographer – Diagnostic Imaging)
**Note presented in numerical order: Figure 1.1, 1.2, 1.3, 1.4**
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