Developmental dysplasia of the hip (DDH)

What is developmental dysplasia of the hip (DDH)?

Developmental dysplasia of the hip (DDH) occurs when the joint that connects the torso with the leg forms abnormally. The hip is a ball-and-socket joint, where the ball is the head of the femur (thigh bone) and the socket is the acetabulum (a cup-shaped opening in the pelvis).

Causes of DDH

While we don't know what causes developmental dysplasia of the hip, we do know that it's more likely to occur in children who have relatives with DDH as well as in those born via breech delivery (with feet or bottom closest to the vaginal canal). It's also slightly more common among firstborns, girls and white children.

Some children are born with DDH, but the condition can also develop as a child grows or even recur after it was treated successfully. This means that a child diagnosed with DDH needs to be monitored by an orthopedic surgeon until they reach maturity. However, after treatment has corrected DDH, your child can live an active life, including full participation in sports.

Types of DDH

The two main types of developmental dysplasia of the hip are:

• Unstable or dislocated. The ball is not situated in the socket or falls out of the socket.
• Stable or subluxated. The ball is in the socket, but the socket is too small or shallow to adequately contain the ball. As a result, the ball shifts around inside the socket.

Think of the head of the femur (thigh bone) as an egg and the acetabulum (opening in the outer side of the hip bone) as a spoon. In the first type of DDH, the egg slips out of the spoon. In the second type, the spoon isn't large or deep enough, so the eggs rolls from side to side on the spoon.

Symptoms of DDH

Developmental dysplasia of the hip is associated with the following:

• Weak hip muscles
• Limping
• Stiffness and loss of hip movement
• Painful arthritis

Stiffness and arthritis are problems that may take years or even decades to set in. A child with untreated or undetected DDH generally doesn't complain, which is why DDH is sometimes called a silent condition – and why it's important for pediatricians to screen children for it.

Diagnosis of DDH

A physical exam may be sufficient to diagnose developmental dysplasia of the hip. A doctor can detect hip instability – when the ball is able to come out of the socket – by feeling for a "clunk" when the child moves their hips. With a dislocated hip, the child has reduced range of motion and the affected lower limb appears shorter than the other side.

Once a child with DDH begins to walk, the dislocated hip will cause them to limp. If both hips are dislocated, the child will waddle from side to side.

Sometimes DDH isn't diagnosed until the teenage years. This typically happens in girls who begin to experience hip pain during physical activity, such as playing sports.

Tests for DDH

If your child's doctor suspects developmental dysplasia of the hip, the next step is a test to confirm the diagnosis.

Confirming DDH in a child younger than 6 months

A child who is under 6 months of age will have an ultrasound. This painless and noninvasive test, which takes about 15 minutes, is done in the doctor's office. The ultrasound images of the ball and socket are used to determine the condition's severity.

Confirming DDH in a child older than 6 months

The best test for a child over 6 months of age is an X-ray. This test is also painless and noninvasive, and the radiation dose is less than the background amount present in the everyday environment.

Treatment of DDH

The best treatment depends on your child's age. Whether the approach is bracing, casting or surgery, the goal is to support the hip joint's normal development, with the femoral head fitting securely into the socket.

Bracing for DDH

For babies under 6 months, treatment is usually bracing the joint with a Pavlik harness. The baby wears the harness full-time, except for half an hour in the morning and half an hour in the evening, to allow for bathing. The Pavlik harness directs the ball into the socket's center, which causes the socket to become deeper and wider.

After the child has worn the harness for one week, we'll perform an ultrasound to make sure the ball is sitting in the socket. Once this is confirmed, the harness is worn for six more weeks.

After six weeks, a second ultrasound is performed to check for signs that the Pavlik harness is continuing to work. If things appear to be progressing well, the child continues to wear the harness, only at night, for another six weeks. If the ball isn’t sitting properly in the socket after this time of wearing the Pavlik harness, use of the harness is discontinued and the child moves to a different treatment.

The success rate of the Pavlik harness is about 90%, which means that about 1 in 10 infants with DDH will need a second phase of treatment.

Closed reduction and casting for DDH

This treatment is for children who are older than 6 months when starting care or for whom the Pavlik harness didn’t work. Closed reduction is a nonsurgical procedure to manually set the hip in place; the child is then put into a custom body cast that keeps the ball in the socket.

For this procedure, performed in an operating room, the child is given a general anesthetic to make the body fully relax. The doctor examines the hips in this loose state, and an arthrogram (joint X-ray) is taken to provide a look at the bones of the joint. The doctor then manually manipulates the hip joint to make the ball sit properly in the socket, a process called closed reduction.

The child is then placed in a spica cast, a type of body cast designed to stabilize the hip joint. This fiberglass cast, which has a soft lining, extends from just below the nipples to the ankle on the affected side and to the knee on the other side. Once the cast is set, the thigh, hip and pelvis will not move.

The spica cast is worn for six weeks, at which point the doctor removes it in the operating room under general anesthesia and repeats the exam and X-rays. If all is well, the child is placed in another spica cast for six more weeks, or longer. The total amount of time a child with DDH needs to spend in a spica cast varies.

For information on caring for your child during this phase, read "Caring for a Child in a Spica Cast."

Open reduction and casting for DDH

If the hip is extremely unstable – for example, if the ball is pushed out by soft tissues that have filled the socket – a spica cast won't be sufficient to fix the problem. In this case, we will perform an open reduction of the hip. During this surgical procedure:

• An incision is made in the groin (on the inside of the thigh) if the child is under 1 year or on the front of the thigh if the child is older.
• One of the muscles in the hip region, the adductor longus, is released (cut) while another muscle, the iliopsoas, is lengthened. The remaining muscles and other soft tissues are moved out of the way so the doctor can reach the hip joint.

The doctor opens the hip joint by cutting the fibrous structure surrounding it and cleans out the soft tissues so that the ball will have room to sit well inside the socket.

After the operation, a spica cast is applied, which the child wears for three months.

Risks of open and closed reduction

The main complication associated with both closed and open reductions is injury that reduces blood flow to the head of the femur. This occurs in about 20 to 40% of cases, although how it happens is unclear, and it may cause the femur head to grow abnormally and become permanently deformed. Over time, this results in arthritis of the hip. The extent of the arthritis depends on how much of the blood supply is cut off as well as how much of the bone is deprived of normal blood flow.

Surgical treatment of DDH

By the time a child with developmental dysplasia of the hip is 18 months old, the joint becomes deformed to the point that it needs to be re-oriented or reshaped surgically. This surgery involves cutting the pelvic bone with or without cutting the thigh bone. The required incision is approximately 10 to 15 centimeters long and made at an angle across the front of the hip.

The cut bones may need to be held in their new position by metal implants, which are removed once the bones have healed together, often several months after the surgery. After this operation, the child typically needs to be in a spica cast for six weeks.

Surgery is also the treatment for teenagers newly diagnosed with DDH. Hip X-rays taken during this stage typically show that the socket is too shallow or small for the ball. In these cases, the best surgical approach is to cut the pelvis and reposition the socket so that it better covers the ball.