To perform Gaenslen's test, the hip joint is flexed maximally on one side and the opposite hip joint is extended, stressing both sacroiliac joints simultaneously. This is often done by having the patient lying on his or her back, lifting the knee to push towards the patient's chest while the other leg is allowed to fall over the side of an examination table, and is pushed toward the floor, flexing both sacroiliac joints. The test can also be performed with the patient in the lateral recumbent position. The patient lies with the involved side up and passively flexes the uninvolved hip as far as comfortable to their chest. The involved hip is taken into extension while stability is maintained in the pelvis. The test is considered positive if the patient experiences pain while this test is performed, and may indicate a need for further testing, such as an X-ray or lumbar CT scan.