The congenital form, teratologic or non-reducible dislocation occurs as part of more complex conditions.The condition can be bilateral or unilateral:

If both hip joints are affected, one speaks of "bilateral" dysplasia. In this case, some diagnostic indicators like asymmetric folds and leg-length inequality do not apply. In unilateral dysplasia only one joint shows deformity, the contralateral side may show resulting effects. In the majority of unilateral cases, the left hip has the dysplasia.If the joint is fully dislocated a false acetabulum often forms (often higher up on the pelvis) opposite the dislocated femoral head position. In acetabular dysplasia, the acetabulum (socket) is too shallow or deformed. The center-edge angle is measured as described by Wiberg. Two forms of femoral dysplasia are coxa vara, in which the femur head grows at too narrow an angle to the shaft, and coxa valga, in which the angle is too wide. A rare type, the "Beukes familial hip dysplasia" is found among Afrikaners that are members of the Beukes family. The femur head is flat and irregular. People develop osteoarthritis at an early age. Causes
Hip dysplasia is considered to be a multifactorial condition. That means that several factors are involved in causing the condition to manifest.The cause of this condition is unknown; however, some factors of congenital hip dislocation are through heredity and racial background.
Hip dysplasia is an abnormality of the hip joint where the socket portion does not fully cover the ball portion, resulting in an increased risk for joint dislocation. Hip dysplasia may occur at birth or develop in early life. Regardless, it does not typically produce symptoms in babies less than a year old. Occasionally one leg may be shorter than the other. The left hip is more often affected than the right. Complications without treatment can include arthritis, limping, and low back pain.Risk factors for hip dysplasia include family history, certain swaddling practices, and breech birth. If one identical twin is affected, there is a 40% risk the other will also be affected. Screening all babies for the condition by physical examination is recommended. Ultrasonography may also be useful.Many of those with mild instability resolve without specific treatment. In more significant cases, if detected early, bracing may be all that is required. In cases that are detected later, surgery and casting may be needed. About 7.5% of hip replacements are done to treat problems which have arisen from hip dysplasia.About 1 in 1,000 babies have hip dysplasia. Hip instability of meaningful importance occurs in one to two percent of babies born at term. Females are affected more often than males. Hip dysplasia was described at least as early as the 300s BC by Hippocrates. Signs and symptoms
Hip dysplasia can range from barely detectable to severely malformed or dislocated.