Case of the Week - Patient Summary 3967Peer Reviewed and Certified -
Pt's medical history was significant for in-utero breech position, delivered via C-section and noted to have a left hip click. Pt was initially referred for a left hip ultrasound to rule out ddh. This US was followed-up approximately one month later with another bilateral hip US.
26July: Bilateral hip US done at follow-up in the standard coronal and axial planes. The right hip is normal, (improved compared to previous). Femoral head 50% covered by acetabulum (alpha angle 59 degrees). Dynamic imaging of right hip shows no evidence of ligamentous laxity. Left hip is approx 40% covered by acetabulum (alpha angle 51 degrees). Left hip does show ligamentous laxity on stress imaging. The impression was persistent ddh of left hip with 40% coverage and a 51 degree alpha angle.
Developmental Dysplasia of the Hip (DDH) On the US films, the femoral head and acetabular articulation is assessed with the alpha angle. Lines are often drawn directly on the film to delineate the articulation. The P line (Perkins line) is drawn vertically in a frontal plain through the iliac crest, tangential to the outer acetabular bony margin, and pointing down the shaft of the femur. The H line (Hilgenreiner line) is drawn perpendicular to the P line, in a horizontal orientation, through the triradiate cartilages (on diagram, where the ilium, ischium, and pubic bones intersect at the acetabulum, in a frontal plane). The A line is tangential to the bony acetabular roof, and forms the acetabular angle at its intersection with the H line. The alpha angle is the intersection between the A and P line. In a shallow acetabular joint, the alpha angle is decreased. Greater than or equal to 60 is a mature hip, 50-59 is physically immature or delayed ossification, 43-49 is subluxable, and less than 43 degrees is dislocated (with or without structural alteration) or severely dislocated. (2)
