This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Owing to the pain in the affected limb the weight of the body is borne mainly on the healthy limb. Viewing the patient anteriorly 'in an early case of the disease the external rotation is readily seen in the eversion of the foot. If the foot itself is normal, rotation takes place at the hip-joint and not at the knee or ankle; therefore a foot that is abnormally turned out indicates that there is something in the hip to cause it to turn out. The affected limb is seen to be held in a position of abduction, out away from the healthy one. The flexion is evidenced by the affected limb being placed a little in advance of the other and by the bending at the groin. If the feet are placed together there may also be flexion of the knee (Fig. 525).
Tilting of the pelvis may or may not be apparent, but it exists and can be demonstrated by a careful examination. Viewed posteriorly, besides the position of the limb as seen from in front, there is in addition a change in the gluteal folds and buttock. The gluteal fold on the affected side is lowered in position and shorter than on the healthy side and the buttock is flattened. The flattening of the buttock is caused by the flexion of the hip. This flexion likewise tends to obliterate the gluteal fold. The difference in height of the gluteal folds is caused by the tilting down of the pelvis on the affected side. An inequality in the lower limbs, whether due to shortening or to malposition, such as flexion, will be visible at once by an inequality of the gluteal folds, one being higher than the other. Flexion deformity is recognized when the patient is standing by the bending at the hip-joint and by the lordosis or hollowing of the back. When the patient is recumbent on a flat surface and both legs are brought straight down so that both knees are in contact with the table, then if flexion is present it causes the lumbar vertebrae to arch and the back to rise from the table. If now the thigh of the affected side is elevated until the back again touches the table the degree of elevation necessary to accomplish this will be the measure of flexion.
The child being flat on its back the pelvis is to be made level by seeing that a line joining the two anterior spines is at right angles to the median line. If abduction is present the limb points away from the median line. It cannot be brought straight down parallel with the sound leg without tilting the pelvis. If measured from the umbilicus to the internal malleolus the affected leg measures more than the sound one. This is called apparent lengthening. If when both limbs are placed in the same degree of abduction and are measured from the anterior spine to the internal malleolus they measure the same, there is no real shortening.
In advanced disease adduction is more common than abduction. This produces an apparent shortening, as shown by measurement from the umbilicus to the internal malleolus; if the sound limb is placed in the same degree of adduction as the affected. one, the distances from the anterior spines will show no actual shortening unless there is a loss of bone or displacement at the hip-joint. The pelvis, instead of being tilted down on the diseased side, is tilted up. Flexion is usually more marked and the foot is usually inverted instead of everted.