Horizontal toit externe angle

The horizontal toit externe angle (HTEA) is a measurement used to assess the anatomy of the hip joint in dogs, in particular the lateral slope of the acetabular roof. It is determined from a 2D CT images in a transversal plane. The dog is placed in dorsal recumbency with hip joints extended, adducted, and rotated slightly internally. Measurement 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 sourcil is defined as a curved area of dense bone on the weight-bearing surface of the acetabulum. It is recognized by its sclerotic, arched appearance that resembles an eyebrow. The horizontal pelvic axis is defined as a line through the center of both femoral heads. The horizontal toit externe angle is the angle between a line that extends from the medial edge of the sourcil (dorsomedial border of the lunate surface) to the lateral edge of the dorsal acetabular rim (dorsolateral border of the lunate surface) and a line that extends laterally from the medial edge of the sourcil, parallel to the horizontal pelvic axis.

Andronescu et al (2015) published the following results for horizontal toit externe angle in relation to osteoarthritis score:

• OA score 0: 18.50 ± 6.35

• OA score 1: 23.72 ± 6.92

• OA score 2: 30.66 ± 9.18

• OA score 3: 21.75 ± 5.72

Lopez et al (2008) found that the horizontal toit externe angle in adult mixed-breed dogs with laxity of the hip joints was 32,70 +/- 8,08° (range 11,40 - 82,90).