Hip dysplasia (“dys” meaning bad or disordered; “plasia” referring to tissue formation) is a comprehensive term for an array of related conditions in which the hip joint fails to form properly – primarily in infants and young children, though symptoms can first appear much later. The problem can range from mild shallowness of the hip socket all the way to complete displacement of the hip joint. To learn more about how hips are put together, go to Hip Anatomy.
Signs and Symptoms
The condition has been recognized as far back as the time of Hippocrates in the fourth and fifth centuries B.C., and was traditionally known as congenital (present at birth) hip dysplasia, or CHD. However, because the condition is not always diagnosable at birth, sometimes appearing later in childhood, in adolescence or even adulthood, it has become known in recent years as developmental dysplasia of the hip, or DDH.
The term DDH encompasses the entire spectrum of abnormal hip development. Acetabular dysplasia represents the mildest form, wherein the hip socket (acetabulum) remains underdeveloped and shallower than normal, which can lead to joint instability and accelerated wear of the joint in some cases. A subluxable hip represents a more unstable situation, with the hip able to be pushed partially out of joint with little force. A dislocatable hip can be slid completely out of joint, and can be put back in (“reduced”) with the opposite maneuver. The most severe form of DDH is a dislocated hip, where the femoral head lies at rest outside the acetabulum, and in some cases cannot manually be reduced.
The prevalence of DDH is commonly reported as approximately one in a thousand among Caucasians, though some researchers put the figure much higher. African-American, Korean and Southern Chinese populations appear to be less affected. However, there seems to be a correlation between cultures where babies are often tightly swaddled (such as certain Nordic peoples, Native Americans and Inuits) and a higher rate of DDH.
DDH is estimated to be four to nine times more common in females than males. The greatest incidence of DDH occurs in first-born females who have a close relative with the condition.
Aside from genetic inheritance, a breech position in utero is definitely associated with a higher incidence of DDH. It is felt that conditions that lead to intrauterine “crowding”-such as a smaller uterus in first time pregnancies, lack of amniotic fluid (oligohydramnios), and multiple births – increase the risk of DDH.
It’s thought that the left hip is more often involved in DDH, because of the common intrauterine positioning of the fetus, which places the left hip against the mother’s sacrum, forcing the hip to contract.
Another theory is that the fetus’s response to the mother’s estrogen during pregnancy may loosen hip ligaments in the joint, allowing slippage of the femoral head in the acetabulum after birth.
Although every baby with DDH manifests symptoms differently (and either one or both hips may be affected), some symptoms are more common than others and may be first observed by a pediatrician during a routine screening shortly after birth. The screening will include a complete family medical history to determine whether any close relative has had the condition or unusually loose ligaments. As the physical findings of DDH can be subtle, and the examination of infants sometimes challenging, it is recommended to have an infant’s hips checked at every medical visit until they are walking age.
The physician will perform a physical examination, manipulating the infant’s hips through specific manoeuvres called Barlow and Ortolani tests. These tests gently move the femoral head out of the acetabulum and then replace it. The ability to do this decreases as the infant grows, and is generally gone by 3 to 4 months. After this time, if the hip remains dislocated, the doctor will look for signs of an established dislocation. This includes determining whether one leg appears to be shorter or whether leg positions appear to be asymmetrical. The doctor will also examine the folds of skin around the buttocks and thighs, as well as the space between the thighs, to see if they appear uneven.
To eliminate the possibility that the symptoms are caused by another condition, the doctor may wish to confirm the diagnosis with an ultrasound. (Because an infant’s joints are still mostly cartilage, rather than bone, x-rays can’t produce a good image.)
Once a diagnosis has been made, and the examination has eliminated any other possibilities, the doctor will prescribe a course of treatment.
If treatment is deemed necessary, the goal is to properly position the femoral head in the acetabulum so the hip can develop normally. Once achieved, the hip must then be held in position until the body has adapted to it. The best results are achieved with early intervention.
In children under six months of age, the technique most often employed is a Pavlik harness, a device fitted to the baby that holds his/her hips in position, properly positioning the hip joint so that it will form normally. It’s essential that babies fitted with a Pavlik harness be checked regularly to ensure proper fit of the device – not too tight, not too loose – so that the hips are held in proper position.
Illustration depicting the Pavlik harness.
In babies older than six months, a Pavlik harness may not be appropriate, in which case other measures may be undertaken. The baby may need a procedure known as a “closed reduction,” during which the hip is positioned manually while the child is under general anesthesia. This is occasionally preceded by a period of traction, in which gentle pulling on the leg by adhesive tapes applied to the skin is used to stretch contracted soft tissues around the hip joint for 7-14 days prior to the closed reduction. If the procedure is successful, the baby will then be fitted with a body cast for the next three to four months, with periodic changes to accommodate the child’s growth and maintain the cast integrity. Once the hip is judged to have achieved a normal position, the cast is removed and a brace fitted in its place. The child will also very likely need to follow a regimen of exercises to ensure proper motion in the hip.
Whatever the approach, the younger the patient when treatment is initiated, the more likely the result will be successful. For infants diagnosed with DDH and fitted with a Pavlik harness in the first six weeks of life, treatment is successful in more than 90% of cases. With later diagnosis, treatment is more complicated, though good results are still achieved in the majority of cases.
After the age of a year to 18 months, treatment can be complex, with multiple procedures, and outcomes aren’t as consistently successful. If residual dysplasia persists, the child may not demonstrate any significant problems in childhood, but is at risk to develop early hip arthritis as a young adult, possibly requiring surgery later in life to cut and realign the bones (a hip osteotomy) or a total hip replacement.