Type 2 dysplasia short roof in type 2 dysplasia the angulation of the roof may be less than 10 but the roof is short providing less coverage of the femoral head.
Normal acetabular roof angle.
An additional measurement of acetabular version was acquired at the center of the femoral head on each side.
5 mm 10 mm 15 mm and 20 mm below the roof.
Acetabular angle defined as the angle made from line through the y synchondroses and another line through the superior and inferior points of the iliac portion of the acetabulum.
Axial reformatted images through the acetabula were used to measure acetabular version angles at four locations with respect to the acetabular roof on each side.
It is measured on ap pelvic radiograph.
At birth it should be less than 28 degrees and should progressively reduce with maturation of the hip.
Values between 3 and 13 are considered within the normal range 2.
Thus the load in weight bearing is distributed across a smaller than normal bone surface area again resulting in labral tear and hip joint degeneration.
A measurement between 39º and 46º is indeterminate.
In this form the femoral head is well positioned but the acetabular roof is short and provides insufficient cover.
Normal values in adults.
3 article feature images from this case.
Less than 39 42 and 55 of medial anterior and posterior acetabular roof arc angles involve absawba of the femoral head.
First a line is drawn running through the medial.
Derived from a line drawn along the lateral bony margin of the ilium and from a line drawn across the bony acetabular roof.
Standing lateral radiograph normal.
An acetabular index or roof angle of less than 10 is normal but more than 10 15 is considered dysplastic with higher risks of instability see graphic above.
Angles above 47º are seen in patients with acetabular dysplasia.
Average medial anterior and posterior acetabular roof arc angles of the absawba of 94 normal acetabulum were 39 09 7 41 42 49 8 15 and 55 26 10 08 degrees respectively.
Additionally having the center beam above or below the pubis can alter the measurement due to geometric distortion.
Increased acetabular index more than 13.
The acetabular angle is a plain film measurement used when evaluating developmental dysplasia of the hip ddh which is measured between hilgenreiner s line and a line parallel to the acetabular roof.
Physiologic acetabular anteversion angles in adults have been declared in the 12 to 20 range 5 7 but seem to be more variable 3 8 probably not least because of the dependence of the distance to the acetabular roof 3.
