Acetabular margin changes in feline hip joints - Implications for radiologic diagnosis and development of osteoarthritis

The development and early morphological features of feline hip osteoarthritis (OA) are largely unknown. Tears in the acetabular labrum and at the chondrolabral transition zone are suggested to be important in the pathogenesis of human hip OA, but in cats such lesions have not been described. We investigated associations between computed tomography (CT)-detected joint changes and microscopic articular cartilage lesions, the distribution of detected changes, and histologically evaluated the acetabular margin (AM) in hip joints from 20 cats. Histologic evaluation was undertaken on at least one joint from each cat. CT-detected joint changes and articular cartilage lesions were graded and the histological appearance of CT-detected osteophytes evaluated. The majority of CT-detected lesions and cartilage lesions were mild. Whole-joint CT scores and AM osteophyte CT scores showed moderate to strong correlation with cartilage scores. The odds were higher for presence of CT-detected osteophytes in craniodorsal, cranial, cranioventral, ventral and dorsal AM regions. Peripheral acetabular regions showed higher cartilage lesion grades than central regions. Tears, seen as fissures/clefts, in labral and perilabral tissues were common. CT-detected AM osteophytes morphologically presented as pointed sclerotic bone, spur-shaped bone or rounded chondro-osteophytes. The results suggest that CT is a valuable tool for diagnosing early feline hip OA. CT-detected osteophytes showed variable histologic morphologies, which may implicate different disease mechanisms and/or disease stages. Tears in the AM could represent an early event in feline hip OA and this warrants further investigation.