Reference lines for measurement of the quadriceps angle.The QA was measured between the line drawn from the origin of the rectus femoris on the ventral aspect of the ilium, corresponding to the cranial margin of the acetabulum, passing through the middle of the femoral trochlea, and a second line drawn from the middle of the trochlea to the tibial tuberosity. The cranio-caudal radiograph of a 13-month-old male West Highland White Terrier, 9.4 kg body weight; the medical report did not reveal lameness, patella luxation and/or cruciate ligament rupture. The QA values were 22.61° on the right and 21.84° on the left.