Kinematic simulations of static radiographs provides discriminating features of multiple hip pathologies

Osteoarthritis is one of the most common causes of ambulatory disability. Developmental dysplasia of the hip (DDH) and femoroacetabular impingement (FAI) may lead to premature osteoarthritis in a young adult population. Current clinical assessments of DDH and FAI include clinical history, static radiological metrics, and physical examinations. Methods involving dynamic radiography such as fluoroscopy are costly and time-consuming for both patient and physician. Therefore, our aim was to simulate dynamic gait on 3D static radiological images of hips to generate "virtual interference" points between the femur and acetabulum with three methods of center-of-rotation (COR): static spherical, dynamic spherical, and dynamic ellipsoidal. We simulated the gait kinematics on pre-segmented CT images for three groups: DDH (N=10), FAI (N=10), and asymptomatic normal (N=11). The femoral head was divided into four medial quadrants to compare the ratios of virtual interference within the regions along the gait cycle and as a temporal mean. We hypothesized that discriminating characteristics would exist between the two pathologies and for the dynamic COR methods to have more discriminating characteristics than the static COR method. For each COR method, we found the temporal mean of virtual interference to be significantly different in almost every region between the hip conditions. The significance was most distinct when using the static spherical method of COR. These results are promising to individual clinical assessments of hip pathologies using static radiographs and ultimately work towards preventing premature hip disease.