Radiography in the pelvis on AP view:
- the acetabular index may be measured as an index of acetabular dysplasia - this is the angle separating a line between the acetabulae and the line through the acetabulum. It should be less than 30ø in the normal hip
- lines drawn longitudinally down the femoral axes should intersect with the lateral lip of the acetabulum and not beyond
- Shenton's line may be non-continuous
- if a horizontal line is drawn between the lowest point of the acetabular element of the ilium, and vertical lines drawn down at the outer limits of the acetabula, the capital epiphsis of the femur should lie in the inner, lower quadrant. CDH moves the epiphysis into the upper, outer quadrant
- there is delay in the production of ossific centres
- the acetabular roof has an upwards slope
Arthrography may be useful where the plain radiograph is inconclusive. Injection first of a radiopaque contrast medium, then of carbon dioxide gas into the joint, allows intra-articular structures to be visualised.
Ultrasonography:
- most valuable up to 3 months since the cartilaginous structure of the skeleton doesn't show up on radiographs
- the angle of the slope of the acetabular roof and contouring of the head are inspected
Reference
- American Academy of Orthopaedic Surgeons. Detection and nonoperative management of pediatric developmental dysplasia of the hip in infants up to six months of age. Mar 2022 [internet publication].