What is DDH?
Dysplasia means abnormal development. DDH refers to a spectrum of abnormalities of an otherwise normal child’s hip ranging from frank dislocation to mild instability. This deviation from normal development usually occurs when the child was a fetus but can occur in early childhood as well. Dislocation means that the ball (upper end of the femur or thigh bone) is completely out of the acetabulum (socket). Subluxation is a situation wherein the ball and socket are partially together. The mildest form refers to babies whose ligaments are abnormally loose and whose hips can slip in and out the joint very easily.

Why is DDH a problem?
If left untreated those hips which are partially dislocated may progress to frank dislocation. Patients with dislocated hips will walk with a limp, have a limb length discrepancy and develop premature arthritis of their hips.

Does this cause pain?
Pain is not a factor with DDH and that makes its diagnosis very difficult in some cases.

Who gets DDH?
One of every 100 children born will have mild DDH; 1 in 1,000 will have a frankly dislocated hip. There are several known factors that are associated with a greater risk of DDH.

• First born
• A relative with DDH (Family history of DDH)
• Female gender (Girls have four times greater frequency than boys)
• Premature birth (More common in babies born before 37 weeks)
• Breech position
• Decreased amounts of amniotic fluid
• Children with certain foot deformities or a tight muscle in their neck
  The left hip is affected in 60%, the right in 20% and both hips in 20% of the cases.

Are there other types of hip dislocation?
Hip dislocation is seen in a number of conditions. The discussion in this section refers to otherwise normal children. The treatment principles for children whose hips are dislocated for other reasons are different.

What causes DDH?
Ligamentous laxity is likely to be the most important factor. The acetabulum (socket) is very shallow at birth. If the ligaments are loose they, may not be able to hold the hip together. Another factor is position in (breech position). First born children may be predisposed because the uterus has not been stretched by prior pregnancy and with labor, further pressures are placed on the hip. There are ongoing studies to further understand the inter-relationships of these factors.

How is the diagnosis made?
In the newborn, physical examination is the basis for the diagnosis. These exams are typically done by your Pediatrician at the time of birth and on subsequent visits to their offices. You may be referred to us for further evaluation if an abnormality is suspected. In addition to physical exam, other diagnostic studies such as an ultrasound may be necessary. The ultrasound study is useful in the young child because so much of the bone tissue in the hip is cartilage and cannot be seen on x-ray. Plain x-rays become useful after a child is one month of age. In older children, other physical signs are present such as limitation of movement in the hip and the observation of different limb lengths. In children who are walking evidence of limp usually is seen.

How does the hip joint normally form?
Hip joint development occurs mainly during fetal life but continues to develop during the first several years of growth. At birth the shallow joint with the femoral head (ball) and acetabulum (socket) are mostly held together by ligaments. With normal movement and eventually weight bearing (walking) the acetabulum deepens and the upper femur changes its shape to the adult pattern. If the hip is not reduced (ball and socket together), these developmental changes can not occur. Therefore, the treatment is directed at putting the ball and socket together and permitting the hip joint to develop. The ball and socket must be held together until the socket deepens enough that the hip stays reduced (in place) on its own.

How is DDH treated?
The treatment of DDH is the subject of whole textbooks. There are varieties of treatments, which are used based on the age of the child at the time of diagnosis. All treatments are directed at placing the hip back into the socket and keeping it there until there has been enough development that the hip will stay in place on its own.

The first treatment option is a Pavlik harness. This is a simple cloth device that keeps the baby’s legs in a position favorable to the development of the hip. The harness needs to be worn full-time because the femoral head (ball) must be held in contact with the acetabulum (socket) in order for the hip joint to develop. To take the harness on and off will also make it more difficult for your baby to adapt to wearing it. Your doctor will advise you as to how long your child will benefit from the harness. Generally 2-3 months is necessary in the newborn. For hips that are simply unstable or subluxated (partially out of the socket) the Pavlik harness is usually all that is necessary.

For the child whose hip is truly dislocated and the children who are older than 6 months, other treatment may be necessary. Closed reduction and cast application is the next level of treatment. For hips that do not become stable and for those that do not reduce (go into the socket) this is often recommended. The term closed reduction means that the bone and joint are put together by manipulation but without surgery. This procedure is done in an operating room with the baby asleep in order that the hips can be examined with the baby fully relaxed. This permits us to judge if the hip can be placed back into the socket and whether it will stay in the socket. At the time of this procedure, water-soluble dye is placed into the hip joint (arthrogram). This dilute solution outlines the ball, which is largely cartilage and not visible on x-ray, and gives us valuable information about the hip joint. If it is judged that the hip can be reduced (ball put back into the joint) and that the reduction is stable (hip will not immediately fall back out again), a spica cast is applied. In order to immobilize the hip, it is necessary to put a cast over the legs and over the trunk. An opening in the perineum (bottom) is made for hygiene. After the cast is applied and the baby is awake, a CT scan is taken. The CT allows us to look at the hips and gives us good information while the cast in place.

If the child is hip cannot be reduced (placed into the socket) or will only partially reduce, surgery is done to loosen the ligaments that are keeping the hip out of the socket. This is a relatively small operation. A spica cast is applied after this surgery as above. The cast is usually used for a period of 3-4 months depending on the case. Because of anticipated growth and to evaluate the reduction of the hip, these casts are usually changed every six weeks. Anesthesia is used for all cast changes. Although cast application is not painful, babies will simply not lie still enough to permit application of a good cast. Usually some form of brace will be used following cast treatment for a variable period of time.

Finally, there are children who require complex surgery. It is beyond the scope of this section to outline all of the possibilities and variations of management. If such treatment is necessary, your doctor will discuss the problem and recommended treatments with you.

Are there complications associated with treatment of DDH?
As with all complex problems, there are possible complications that have been identified. Treatment can be difficult and, of the many options, some will not work on a given patient. Loss of blood supply to the femoral head (ball) is seen in the treatment of DDH. This problem has been reported even in the basic treatment with a Pavlik harness and increases in probability if surgery is necessary. Your doctor will discuss these issues with you.

Why should I put my child through treatment?
Treatment for most patients with DDH is completed by the time the child is 6 months of age. For those children who have had a more difficult problem and may require a cast for their treatment, it is usually completed by the time they are walking. In many ways, the difficulty of treatment is largely for the caregiver. The bottom line is: in order for a hip to develop normally, it must be properly placed in the socket. For those whose hips are not properly placed, premature arthritis, limping, and limb length discrepancy are real problems. In order for your child to run and play actively and without limitation, treatment is clearly the best option.

More information:
http://www.aap.org/policy/ac0001.htm
http://www.orthop.washington.edu/faculty/Diab/ddh/03
http://www.drhull.com/EncyMaster/H/hip_dysplasia.html