Central angle intersection points and of the legs of the angle with the circle form a diameter, then is a straight angle. (In radians, .) Let be the minor arc of the circle between points and , and let be the radius of the circle. If the central angle is subtended by , then If the central angle is not subtended by the minor arc , then is a reflex angle and If a tangent at and a tangent at intersect at the exterior point , then denoting the center as , the angles (convex) and are supplementary (sum to 180°). A
Straight leg raise more specific, the ankle can be dorsiflexed and the cervical spine flexed. This increases the stretching of the nerve root and dura. If the patient experiences sciatic pain when the straight leg is at an angle of between 30 and 70 degrees, then the test is positive and a herniated disk is a possible cause of the pain. A negative test suggests a likely different cause for back pain. A meta-analysis reported the accuracy as: If raising the opposite leg causes pain (cross or contralateral straight leg raising): Lasègue's sign was named after Charles Lasègue (1816-1883). In 1864 Lasègue described