The four-digit symbol ( Patrick's test ) is a simple manual examination method. When examining orthopedic patients, it is used as one of several clinical tests in the functional testing of the hip joint and sacroiliac joint or lower spine. A positive four-digit sign is found in Perthes' disease (juvenile femoral head necrosis) and also in other diseases of the hip joint (e.g. coxitis ) and the sacroiliac joint.
In the four-stage test, several possibilities of movement of the hip joint such as flexion , abduction and external rotation (complex function test) are tested at the same time . When lying down, the foot of the leg to be assessed is placed against the knee joint of the other leg in such a way that a flexion of approx. 45 ° in the hip and 90 ° in the knee is created. In healthy patients, a 4 is described by taking the position described from above . Now the patient should spread the leg outwards so that it comes as close as possible to the base; the examiner holds the hip joint on the opposite side to the surface. The minimum distance between the outside of the knee ( condyle lateralis femoris ) and the surface should be less than 20 cm. If this distance is greater, because, for example, the abduction is limited in the diseased hip joint with simultaneous external rotation, this is called a positive four-digit sign. The test is particularly meaningful when comparing the sides of the hip joints. If the patient remains passive and the knee is pressed down by the examiner, the appearance of pain signs in the hip joint can also be assessed.
If the mutual hip joint is not fixed during the examination, the lumbar spine will also rotate. This is used to investigate a possible painfulness in this area, with the knee being pressed towards the surface. In typical diseases such as facet syndrome ( arthrosis of the small vertebral joints), pain in the back occurs with pain radiating to the legs. Previous pain in the hip joint must be excluded.