Developmental dysplasia of the hip (DDH or hip dysplasia) is a relatively common condition in the developing hip joint. It occurs once in every 1,000 live births. The hip joint is made up of a ball (femur) and socket (acetabulum) joint. In DDH, this joint may be unstable with the ball slipping in and out of the socket.
In addition, the socket is often shallow which can increase a person’s risk of developing arthritis and joint pain later in life. Hip dysplasia has wide spectrum of severity ranging from a mildly shallow hip socket to a completely dislocated hip.
The greatest incidence of DDH occurs in first-born females with a history of a close relative with the condition and/or history of breech position in utero.
The exact cause(s) of hip dysplasia are unknown, but it is likely that many factors both environmental and genetic play a role.
One of the environmental influences thought to contribute to hip dysplasia is the baby's response to the mother's hormones during pregnancy. A tight uterus that prevents fetal movement or breech position may also cause hip dysplasia. The left hip is involved more frequently than the right due to intrauterine positioning.
Another environmental factor is infant positioning in the first year of life. Cultures that hold infants wrapped around a caregiver such that the hips are held apart generally have lower rates of DDH. In contrast, cultures which typically swaddle or papoose an infant with the hips extended have high rates of hip dysplasia.
First-born babies are at higher risk since the uterus is small and there is limited room for the baby to move; therefore affecting the development of the hip. Other risk factors may include the following:
- Family history of developmental dysplasia of the hip, or very flexible ligaments
- Position of the baby in the uterus, especially with breech presentations
- Associations with other orthopaedic problems that include metatarsus adductus, clubfoot deformity, congenital conditions, and other syndromes
- Frequent swaddling with the hips out straight (extended)
The symptoms of hip dysplasia are often very subtle during the newborn period. Hip dysplasia is painless during infancy and early childhood though it can cause pain and disability later in life if left untreated. Characteristic findings which raise a suspicion for DDH include:
- The leg that appears shorter on the side of the dislocated hip
- The affected leg not spreading (abducting) as widely as the normal side
- The folds in the skin of the thigh or buttocks may appear uneven
- A “clunk” felt with diaper changes or other positioning of the leg
If unrecognized until later in life, children with DDH will still typically learn to walk at a normal age. Depending on the severity of hip dysplasia, a child may have a limp or “waddle” with walking or running.
Pain and leg length differences can develop during adolescence. During adulthood, residual shallowness in the hip socket is thought to be the number one cause of arthritis and therefore the most common reason for why an adult may require a hip replacement (artificial joint).
Developmental dysplasia of the hip is sometimes noted at birth. The pediatrician or newborn specialist screens newborn babies in the hospital for this hip problem before they go home.
Your baby's physician may make the diagnosis of developmental dysplasia of the hip with a clinical examination. During the examination, the physician obtains a complete prenatal and birth history of the baby and asks if other family members are known to have DDH. However, DDH may not be discovered until later evaluations and not all hip dysplasia can be determined by physical examination alone.
Diagnostic procedures may include:
- ultrasound (Also called sonography.) - a diagnostic imaging technique which uses high-frequency sound waves and a computer to create images of the baby hip joint. This tests uses no radiation and is best when for younger infants in whom most of the hip joint is still made of cartilage (<6 months of age)
- X-ray - a diagnostic test which uses invisible electromagnetic energy beams to produce images of the hip joint. This is the standard test used to diagnose or monitor DDH after 6 months of age.
- computed tomography scan (Also called a CT or CAT scan.) - a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, of the body. A CT scan shows detailed images of the hip and can help assess the three dimensional shape of the bones and joint. CT scans are not typically used for diagnosis but may be used to confirm hip position after treatment.
- magnetic resonance imaging (MRI) - a diagnostic procedure that uses a combination of large magnets, radiofrequencies, and a computer to produce detailed images of the hip. MRIs do not expose infants to any radiation and are the best imaging test to look at the soft tissues (ligaments, muscle, tendons) around and in the hip joint.
Specific treatment for DDH will be determined by your baby's physician based on:
- Your baby's gestational age, overall health, and medical history
- The severity of the condition
- Your baby's tolerance for specific medications, procedures or therapies
- Your opinion or preference
The goal of treatment is to put the femoral head back into the socket of the hip and to deepen the socket so that the hip can develop normally. Treatment options vary for babies and may include:
The Pavlik harness is used on babies up to 6 months of age to guide the hip into place, while allowing the legs to move a little. The harness is put on by your baby's physician and is usually worn full time for several weeks, then part-time for an additional number of weeks.
Your baby is seen frequently during this time so that the harness may be checked for proper fit and to examine the hip. During the course of treatment, ultrasound (or x-ray) will be used to check hip placement and the development of the socket.
Most hips in infants can be successfully treated with the Pavlik harness, but sometimes, they may continue to be partially or completely dislocated.
If the hip continues to be partially or completely dislocated, the second line of treatment is an abduction brace, which is more rigid and can be used beyond 6 months of age in older and bigger infants.
These braces generally allow less motion than a Pavlik harness and are therefore more restrictive but can be quite successful for those infants in whom the Pavlik does not work.
Body casting (spica casting)
If the harness and/or brace are not successful, a procedure under anesthesia may be required to put the hip back into place manually, also known as a closed reduction. If successful, a custom molded body cast (called a spica cast) is put on the baby to hold the hip in place. The hip spica cast is usually applied from the chest down to the ankle of the affected side and usually includes part of the opposite leg as well.
The spica cast is worn for approximately three to six months. The cast is changed from time to time to accommodate the baby's growth and for hygiene reasons. Following casting, a brace and/or physical therapy may be necessary to promote deepening of the hip socket and strengthen the muscles.
Cast care instructions:
- Keep the cast clean and dry.
- Check for cracks or breaks in the cast.
- Rough edges can be padded to protect the skin from scratches.
- Do not scratch the skin under the cast by inserting objects inside the cast.
- Use a hairdryer placed on a cool setting to blow air under the cast and cool down the hot, itchy skin. Never blow warm or hot air into the cast.
- Do not put powders or lotion inside the cast.
- Cover the cast during feedings to prevent spills from entering the cast.
- Prevent small toys or objects from being put inside the cast.
- Elevate the cast above the level of the heart to decrease swelling.
- Do not use the abduction bar on the cast to lift or carry the baby.
When to call your baby's physician:
Contact your baby's physician or healthcare provider if your baby develops one or more of the following symptoms:
- Increased pain
- Increased swelling above or below the cast
- Drainage or foul odor from the cast
- Cool or cold toes
If a closed reduction is not successful, the next line of treatment is surgery in the form of an open reduction, to reposition the ball within the socket.
This involves an incision, opening of the hip joint itself, and directly visualizing the ball and socket. After open reduction infants will require a spica cast but generally for less time than after a closed reduction.
Newborn screening for DDH has allowed for earlier detection of this hip condition. If identified early, treatment generally entails a harness or brace and is quite successful. The older a child presents, the more likely that surgery will be necessary.
Continued follow-up even after successful treatment of DDH in an infant is very important because as a child grows into an adolescent the socket needs to be monitored to be sure that it, too, is developing properly. Occasionally, additional surgeries will be needed to help deepen a socket and minimize the risk of arthritis as an adult.