Developmental dysplasia of the hip is a problem with the way that the hip joint develops. It is usually present from birth and is more common in girls. When developmental dysplasia of the hip is diagnosed and treated early in a young baby, the outcome is usually excellent. If treatment is delayed, the treatment is more complex and with less chance of being successful.
Understanding the hip joint
The hip joint is where the head of the femur (rounded top of the thigh bone) meets the pelvis. It is called a ball and socket joint. The ball is the head of the femur and the socket is the acetabulum.
The acetabulum is a rounded cup-like structure within the pelvis which the head of the femur sits in. The diagram on the right shows the normal structures.
What is developmental dysplasia of the hip?
Developmental dysplasia of the hip (DDH) is an abnormality in the hip joint that is usually present from birth.
DDH was previously known as congenital dislocation of the hip (CDH). It was renamed to show better how there are different degrees of abnormality (not just dislocated hips).
In a normal hip, the head of the femur is a smooth rounded ball and the acetabulum is a smooth cup-like shape. The head of the femur and the acetabulum are in close contact, a little bit like an egg in an egg cup.
In DDH, there is an abnormality either in the shape of the head of the femur, the shape of the acetabulum, or the supporting structures around them. As a result, the acetabulum and femur are not in close contact. It may be a mild abnormality where there is some contact between them. This is called subluxation. It may be a severe abnormality where there is no contact between them and this is called dislocation.
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. Only 1 in 75 babies with a risk factor have a dislocated hip. Risk factors include:
- Family history. If there is a parent, brother or sister with DDH then this makes it five times more likely than normal for a child to have DDH.
- 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 fetus (the unborn baby). This makes the ligaments stretchier and means that the bones are more likely to move out of position.
- Pregnancy conditions. If there is only a small amount of fluid in the womb (uterus) 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.
- 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. Most breech babies are born by caesarean section. These babies have a risk of DDH seven times higher than normal. (The risk of DDH for a breech baby delivered vaginally is 17 times higher than normal.)
- Firstborn baby. About 6 in 10 cases of DDH occur in firstborn children. This may be because the uterus is tighter and less elastic than in future pregnancies so that the baby has less room to move.
- Other abnormalities. If the baby has cerebral palsy, spinal cord problems or other nerve and muscle disorders, this increases the risk of developing DDH. DDH is also more common in premature babies or babies born weighing more than 5 kg.
- 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 due partly to the position that Native American babies are swaddled in.
How common is developmental dysplasia of the hip?
DDH occurs in about 1 in 1,000 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 more often than the right one. In about 2 in 10 cases, DDH affects both hips.
What are the symptoms and signs of developmental dysplasia of the hip?
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 the baby's knees and turn the thighs outwards, a bit like opening a book. Whilst 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:
- The skin folds between the legs and the body may not be equal on both sides.
- The femur may look shorter on one side. Your doctor can do an examination to check for these. In about 1 in 4 normal babies there are unequal skin folds, so it is not such an important finding.
Examining babies' hips is difficult. The baby needs to be out of its nappy and relaxed, not crying. Ideally, babies should be examined within 24 hours of birth, at the 6-week check, between 6-9 months of age, and at walking age.
In older children with DDH who are walking, they may have a limp in their walk. This should raise the suspicion of DDH. The child may also walk on its toes. It is not common for DDH to cause a delay in walking though.
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 because the tissues are soft and lax. In most babies, the hip will become stable by itself by two months, as the soft tissues tighten. Sometimes, just by examining a newborn baby's hips, a dislocated or subluxed hip can be relocated into the correct position and be made stable.
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 aged 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. The success rate of simple non-surgical treatments reduces significantly after 7 weeks of age. Commonly used treatments are as follows:
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 6 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. The harness is adjusted as the child grows and as the hip stabilises.
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 (about 2 in 100 babies treated with the harness) 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 6 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.
If the above options fail or your child is much older when DDH is diagnosed, then an operation is needed. 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 with less chance of success once your child's bones have fully developed. Even at this stage though, treatment can still provide a long-term outcome which is better than the alternative of no treatment.
What is the outlook (prognosis)?
Most children who are diagnosed early and treated before the age of 6 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. About 3 in 10 hip replacement operations done in people under the age of 60 years are because of DDH (either untreated, unsuccessfully treated, or delayed in treatment).
Further help & information
Dr Tim Kenny
Dr Colin Tidy
Dr John Cox