A 7-year-old sexually intact male Boxer was evaluated for a 4-week history of lameness in the left hind limb. The lameness had appeared acutely after moderate outdoor activity. The dog had been treated with nonsteroidal anti-inflammatory medication and cage rest by the referring veterinarian with minimal improvement. On examination, the dog had a toe-touching lameness in the left hind limb. Physical examination revealed crepitus, medial buttress, joint effusion, and signs of moderate discomfort on flexion and extension of the left stifle joint. There was also mild atrophy of the left hind limb musculature. Neither cranial drawer nor cranial tibial