Hip instability was increased in proportion to the severity of acetabular dysplasia. A 3D MRI voxel-based registration technique can show in vivo morphology and kinematics of the native hip without exposure to radioactivity.

To examine the clinical features of vertebral and non-vertebral fractures in patients with rheumatoid arthritis (RA), including insufficiency fractures, and to assess the risk factors for fracture, we prospectively studied 209 outpatients with rheumatoid arthritis for 1 year. The age, gender, Steinbrocker's functional class, glucocorticoid use, history of lower limb surgery, serum C-reactive protein (CRP), and use of bisphosphonates were evaluated. Examination for fractures was performed by radiography, computed tomography (CT), magnetic resonance imaging (MRI), and bone scanning. Thirty-three fractures occurred in 24 patients over the 1-year study period, and the incidence was 15.8 fractures per 100 patient-years. Fractures occurred at various sites. The majority (70%) was insufficiency fracture, and more than 50% caused ambulatory dysfunction. Radiographic findings were absent in 39% of the fractures at the onset of pain. The functional class and glucocorticoid dose were significantly associated with fracture development. This prospective study showed that the incidence of fractures, especially insufficiency fractures, was very high in patients with rheumatoid arthritis and that most of their fractures caused gait disturbance. Early intervention to prevent secondary osteoporosis is recommended to maintain the quality of life in patients with rheumatoid arthritis, especially those with functional impairment or undergoing glucocorticoid therapy.

The proposed method for measuring articular cartilage using a 3D-digitizer and 3D-CT was accurate and reproducible. In the elderly individuals, acetabular articular cartilage tended to be thicker in the superolateral area and there was the thinnest category (0-0.5 mm) on the posteroinferior lunate surface of the acetabulum. The contour generated along 480 Hounsfield units (HU) was closest to the subchondral bone contour in the elderly hip.

Our objectives were to clarify the 3D articular contact areas of the in vivo normal hip joint and acetabular dysplasia during specific positions using magnetic resonance imaging (MRI), voxel-based registration, and proximity mapping. Forty-two normal and 24 dysplastic hips were examined. MRI was performed at four positions: neutral; 45˚flexion; 15˚extension; and the Patrick position. Femur and pelvis bone models were reconstructed at the neutral position and superimposed over the images of each different position using voxel-based registration. The inferred cartilage contact and bony impingement were investigated using proximity mapping. The femoral head translated in the anterior or posteroinferior, anterosuperior, and posteroinferior direction from neutral to 45˚flexion, 15˚extension, and the Patrick position, respectively. Multiple regression analyses showed age, femoral head sphericity, and acetabular sphericity to be associated with higher hip instability. The present technique using subject-specific models revealed the in vivo hip joint contact area in a population of healthy individuals and dysplastic patients without radioactive exposure. These results can be used for analyzing disease progression in the dysplastic hip and pathogenesis of acetabular labral tear. ß