Normal Acetabular Roof Angle

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.

Normal acetabular roof angle.

Additionally having the center beam above or below the pubis can alter the measurement due to geometric distortion. Less than 39 42 and 55 of medial anterior and posterior acetabular roof arc angles involve absawba of the femoral head. Standing lateral radiograph normal. Angles above 47º are seen in patients with acetabular dysplasia.

First a line is drawn running through the medial. 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. At birth it should be less than 28 degrees and should progressively reduce with maturation of the hip. 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.

Developmental dysplasia of the hip. The normal range is 33º to 38º. 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. Normal values in adults.

Derived from a line drawn along the lateral bony margin of the ilium and from a line drawn across the bony acetabular roof. 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. An additional measurement of acetabular version was acquired at the center of the femoral head on each side. Increased acetabular index more than 13.

Values between 3 and 13 are considered within the normal range 2. 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. 3 article feature images from this case. A measurement between 39º and 46º is indeterminate.

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. In this form the femoral head is well positioned but the acetabular roof is short and provides insufficient cover. It is measured on ap pelvic radiograph.