What causes developmental dysplasia of the hip?
The cause is not clear. However, there are factors that are known to contribute to the chance of a baby being born with DDH. These include:
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Family history. If there is a parent, brother or sister with DDH, then this makes it 10 times more likely for a child to have DDH.
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Gender. About 8 in 10 cases of DDH are female. This may be due to oestrogen (the female hormone) that is made by the female foetus (the unborn baby). This makes the ligaments stretchier and means that the bones are more likely to move out of position.
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Pregnancy conditions. If there is only a small amount of fluid in the uterus (womb) this is called oligohydramnios. This can increase the risk of developing DDH because the baby is not able to move about within the uterus as much.
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Breech position. If an unborn baby is in the breech position (feet down position in the uterus), this can put the legs in a position which increases the risk of DDH.
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First born baby. About 6 in 10 cases of DDH occur in first born children. This may be because the uterus is tighter and less elastic than future pregnancies so that the foetus has less room to move.
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Other abnormalities. If the baby has cerebral palsy, spinal cord problems or other nerve and muscle disorders, this increases the risk of developing DDH.
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Race. The risk of a child having DDH is much greater in certain races. For example, DDH is much more common in Native American children and much less common in Chinese and African American children. This may be partly due to the position that Native American babies are swaddled in.
How common is developmental dysplasia of the hip?
DDH occurs in about 1 in 1000 babies. It is more common in the left hip. This is thought to be due to the fact that most unborn babies lie against the mother’s spine on their left side. This position may put more pressure on the left hip and cause it to develop abnormally. In about 2 in 10 cases, DDH affects both hips.
What are the symptoms and signs?
A newborn baby with DDH is not distressed or in pain. Soon after birth, most babies are examined by a hospital doctor. One of the problems the doctor is looking for is DDH. The doctor will bend and turn the legs outwards. While doing this, the doctor feels for a clunk, which feels similar to when a light switch is turned on. If the doctor feels this, then it may indicate that there is a problem with the hip.
Two other signs of hip problems are: 1) the skin folds between the legs and the body may not be equal on both sides; 2) the femur may look shorter on one side. Your doctor can do an examination to check for these.
In older children who are walking, they may have a limp in their walk. This should raise the suspicion of DDH.
How is developmental dysplasia of the hip diagnosed?
When DDH is suspected in a newborn baby, you may simply be advised to return for a review examination in a few weeks. This is because the hip may be unstable at birth in many newborn babies. In most babies, the hip will become stable by itself by two months.
If the instability persists on review then, for a baby up to 4-6 months old, an ultrasound scan may be done. This gives a good picture of whether there is a problem with the hip joint or not. (An ultrasound scan is a painless test that uses sound waves to detect structures in the body. It is the same type of scan that is done routinely on pregnant women early in their pregnancy.)
In children over 4-6 months, an X-ray is more helpful. Various measurements are taken on the X-ray picture of the pelvis and femur to determine whether a child has DDH.
What is the treatment for developmental dysplasia of the hip?
Treatment is needed because if the head of the femur is left in an abnormal position then the hip joint develops abnormally.The earlier treatment is started after birth, the greater the likely success of treatment and the lower rate of long-term complications.
The goal of treatment is to relocate the head of the femur into the acetabulum. This then allows the structures of the rapidly developing hip joint (femur, acetabulum, supporting ligaments, etc) to become established normally. The treatment goal can be achieved through a variety of methods, depending on the age of your child. Commonly used treatments are as follows:
Pavlik harness
This is a device that is used to hold the hips in the correct position. It is often the first treatment used in children under six months old. It usually needs to be worn for at least six weeks full time and six weeks part time in young babies. Older babies may need to wear it for longer. During this time, ultrasound scans are usually done to check that the hip is in the correct position. This harness keeps the legs bent and turned outwards, but allows certain movements. It does not allow your child to straighten their legs or turn them inwards.
For mild DDH (subluxation) this harness works in more than 9 in 10 children if used at this young age. In severe DDH (dislocation) the harness is effective in about 8 in 10 children. The main possible complication of the harness is called avascular necrosis. This is uncommon but sometimes occurs if the hip is not held in the correct position. (Avascular necrosis means that the bone tissue at the head of the femur dies due to undue pressure on the blood supply to the bone.)
Closed reduction and hip spica
This method is used in children over six months of age, or if the Pavlik harness is not effective. This involves your child being given an anaesthetic. While they are anaesthetised, the doctor positions the hip the correct way and then applies a special cast or plaster to keep the hip in the right position. The position of the hip is confirmed as correct by an MRI or CT scan done after the procedure. This cast is kept on for at least 12 weeks.
Open reduction
If the above options fail or your child is much older when DDH is diagnosed, then your child will need an operation. The operation involves loosening the tendons around the hip and removing anything that is stopping the hip from moving freely. Once the bones are in a good position, the joint is strengthened.
Other types of surgery
If DDH has not resolved by 18 months, more complicated surgery is required. This involves removing some parts of the bone and joint so that the hip can be kept in the right position.
What if developmental dysplasia of the hip is not treated?
If your child’s DDH is not diagnosed and treated early, they may develop early arthritis of the hip joint. This causes pain and reduced movement. The treatment of DDH gets more complex and less successful once your child’s bones have fully developed. Even at this stage though, treatment can still provide better a long-term outcome than no treatment.
What is the outlook (prognosis)?
Most children who are diagnosed early and treated before six months have an excellent outcome. However, they will usually need to be reviewed with X-ray pictures taken throughout childhood until their bones have fully developed. The outlook is less good if the diagnosis or treatment is delayed, especially if the child has begun to walk before DDH is diagnosed.
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions.
© EMIS 2008 Reviewed: 14 Nov 2008
