Center-edge angle

The centre-edge angle is a measurement used to assess the anatomy of the hip joint in dogs. It quantifies the extent of lateral and dorsal coverage of the femoral head and is used to score coxofemoral dysplasia. It is determined from a ventrodorsal radiograph of the hips or 2D CT images in the transverse plane.

For radiographic evaluation

The dog is placed dorsal recumbency and the pelvic limbs are extended caudally, the femurs are parallel to each other. Positioning is considered satisfactory if :

• the pelvis is symmetrical (iliums and obturator foramina are symmetrical)

• the femur cortex pass through the middle of the sesamoid bones of the gastrocnemius muscle

• the patellas are centered on the trochlea of femur.A best fit circle delimiting the femoral head is drawn and the centre of this circle is positioned. The center-edge angle is the angle between the line extending from the center of the femoral head, tangential to the craniolateral acetabular rim and a line parralel to the the iliac axis.

A best fit circle delimiting the head of femur is drawn and the centre of this circle is positioned. The center-edge angle is the angle between the line extending from the center of the femoral head, tangential to the craniolateral acetabular margin and a line parrallel to the the iliac axis.

Mostafa et al. 2022 published the following results for the center-edge angle in Labrador retrievers:

• Normal hip joints : 28,1 +/- 3,6 °

• Near normal hip joints : 27,7 +/- 3,6°

• Mild hip dysplasia : 20,4 +/- 3,7°

• Moderate hip dysplasia : 12,7 +/- 3,8°

• Severe hip dysplasia : -0,48 +/- 8,1°

For CT evaluation

The dog is placed in dorsal recumbency with hip joints extended, adducted, and rotated slightly internally. Measurment is performed on three contiguous images that include an acetabular fossa, a well-defined acetabular sourcil, a round head of femur, and a fovea capitis.

The center edge angle is the angle between a line that extends from the center of the femoral head to the dorsolateral point of the labrum and a line perpendicular to the horizontal axis of the pelvis that extends dorsally from the center of the femoral head. The horizontal axis of the pelvis is defined as a line through the center of both femoral heads.

Andronescu et al (2015) published the following results for Center edge angle (CT scan) in relation to osteoarthritis score:

• OA score 0: -2,30 +/- 7,87°

• OA score 1: -12,38 +/- 10,56°

• OA score 2: -11,86 +/- 19,35°

• OA score 3: -20,60 +/- 20,71°

Lopez et al (2008) found that the center-edge angle in adult mixed-breed dogs with laxity of the hip joints was -11,96 +/- 6,86° (range -62,20 - -5,23)