Hip Arthritis on X-ray: Imaging Findings

The Tonnis grading system classifies hip osteoarthritis on AP pelvis radiographs. Grade 0 indicates no signs of arthritis. Grade 1 shows increased sclerosis of the femoral head or acetabulum, slight joint space narrowing, and minimal osteophyte formation. Grade 2 demonstrates small cysts, moderate joint space narrowing to less than 50% of normal, and moderate head deformity. Grade 3 reveals large cysts, severe joint space narrowing or obliteration, severe head deformity, and osteonecrosis. Treatment escalates with grade: grades 0–1 are managed conservatively, grade 2 may warrant joint-preserving procedures, and grade 3 typically necessitates total hip arthroplasty.

The lateral center-edge angle (LCEA), measured on an AP pelvis radiograph, quantifies acetabular coverage of the femoral head. A normal LCEA ranges from 25° to 39°. An LCEA below 25° indicates lateral uncoverage (hip dysplasia), which concentrates joint reaction forces on a reduced contact area and accelerates cartilage degeneration, producing early-onset arthritis in young adults. Conversely, an LCEA above 40° signals over-coverage associated with pincer FAI morphology. Both extremes predispose the hip to osteoarthritis through different mechanical pathways, and identifying acetabular morphology is essential for surgical planning in younger patients.

Yes. Radiographic joint space narrowing reflects substantial cartilage loss that has already occurred, whereas MRI — especially T2 mapping and dGEMRIC (delayed gadolinium-enhanced MRI of cartilage) sequences — can detect biochemical changes in articular cartilage proteoglycan content before structural degradation becomes visible. Standard MRI also identifies early subchondral bone marrow edema, synovial hypertrophy, small effusions, and labral pathology in pre-arthritic hips. These findings help stratify patients who may benefit from joint-preserving surgery before irreversible cartilage loss narrows their treatment options.