Derived from a line drawn along the lateral bony margin of the ilium and from a line drawn across the bony acetabular roof.
Normal acetabular roof angle.
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.
An additional measurement of acetabular version was acquired at the center of the femoral head on each side.
In this form the femoral head is well positioned but the acetabular roof is short and provides insufficient cover.
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.
5 mm 10 mm 15 mm and 20 mm below the roof.
Normal values in adults.
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.
It is measured on ap pelvic radiograph.
Additionally having the center beam above or below the pubis can alter the measurement due to geometric distortion.
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.
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.
A measurement between 39º and 46º is indeterminate.
3 article feature images from this case.
Developmental dysplasia of the hip.
Standing lateral radiograph normal.
The acetabular index also called acetabular roof angle or tönnis angle is a radiographic measurement of femoral head bony coverage by the acetabulum it is useful in assessing for developmental dysplasia of the hip ddh as well as pincer morphology in femoroacetabular impingement fai.
Angles above 47º are seen in patients with acetabular dysplasia.
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.
Increased acetabular index more than 13.
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.
At birth it should be less than 28 degrees and should progressively reduce with maturation of the hip.
The normal range is 33º to 38º.
