Intra-articular osteoma in the stifle joint of a cat

CASE SUMMARY: A 13-year-old male castrated cat was referred to our clinic for a 2-month history of right hindlimb lameness. Radiographs and CT showed a solid bony mass within the stifle joint. The mass was resected by arthrotomy and osteotomy of the tibial tuberosity. Histopathological examination revealed the diagnosis of osteoma. Recovery from surgery was uneventful. At the 8-week follow-up examination, the cat was free of clinical signs. RELEVANCE AND NOVEL INFORMATION: Feline osteomas are rare; only few cases have been reported. To the best of our knowledge, this is the first report of an intra-articular osteoma in the stifle joint of a cat and description of its surgical resection.