Developmental dysplasia of the hip (DDH), also known as developmental pediatric dysplasia of the hip or hip dysplasia, describes a spectrum of hip joint abnormalities that vary in severity from a complete dislocation of the hip joint to mild irregularities of the located hip joint.
Hip dysplasia may develop in a baby around the time of birth or during early childhood. Although it is commonly diagnosed in babies and young children, DDH also affects adolescents and adults. This can usually be attributed, however, to milder cases of DDH that are difficult in diagnose and may be untreated as a child.
In the healthy hip joint, the upper end of the femur (thighbone) meets the acetabulum to fit together like a ball and socket, in which the ball rotates freely in the socket. Cartilage, a smooth protective tissue, lines the bones and reduces friction between the surfaces during movement.
In DDH, however, there is an abnormal relationship between the components of the hip, and often the hip socket is underdeveloped and does not support the femoral head (ball).
The conditions encompassed by the term hip dysplasia include:
In children, hip dysplasia more frequently affects the left hip than the right. About 80% of cases follow this pattern. The condition can, however, be present in both hips.
Some mild forms of developmental hip dysplasia in children – particularly those in infants – can correct on their own with time.
Hip dysplasia is much more common in girls than in boys, and it tends to run in families. Even among children who have no hereditary link, there is a greater risk in all first-born children.
Genetics plays a strong role, but other influences during pregnancy and birth – such as congenital conditions caused by the fetus being in a uterus that is too small – and cases of breech birth can also lead to developmental hip dysplasia.
The risk of hip dislocation at birth is approximately one in 1,000. If a parent experienced hip dysplasia during childhood, the risk of his or her own child developing this risk increases by 12% compared to a parent with no history of the condition. A child whose sibling has hip dysplasia will have a 6% higher chance of developing the condition.
Head tilt (torticollis) and the turning in of the front of the foot (metatarsus adductus) are congenital conditions that often the result of being constrained in a uterus that is too small. These conditions alert medical professionals to be on the lookout for the presence of hip dysplasia, which can also be caused by such constraint.
This is when the baby emerges from the birth canal buttocks-first instead of headfirst. A breech-birth child is 10 times more likely to develop hip dysplasia than a child born headfirst.
When present at birth, the abnormality may be detected during a routine physical examination of the newborn baby. Other signs include a leg length discrepancy, restricted range of motion in the hip, or a limp or waddle in walking in toddlers.
During a routine examination of a newborn, the physician gently flexes the child's hips in different directions. If the hip is dislocated or can be easily dislocated or subluxated (partially dislocated), the doctor may feel a "clunk" as the hip moves out of alignment. In a smaller percentage of cases, the problem does not become apparent until later in infancy or early childhood. Later diagnosis of hip dysplasia may be detected during routine examinations of hip stability in the pediatrician's office.
Additional signs that may bring undiagnosed developmental hip dysplasia to the attention of parent and physician include:
To confirm a diagnosis of developmental hip dysplasia in children up to four to six months of age, an orthopedist uses ultrasound imaging. This technology offers a significant advantage over conventional a X-ray because images may be taken while the hip is in motion. "This is a very accurate and safe diagnostic tool since there is no radiation," according to Roger F. Widmann, MD, Chief of Pediatric Orthopaedic Surgery at HSS. In children older than six months, X-rays, which show bone detail better, are used to confirm the diagnosis.
Early intervention is essential to ensure the bones that make up the hip joint develop properly. Incorrect growth in either the ball or socket can cause formation problems in the other. The goal is to achieve and maintain joint congruity. "The acetabulum and the femoral head are dependent on one another for normal growth and development," explains Dr. Widmann. "If the ball does not fit tightly into the socket, providing a specific growth stimulus, the socket may become too flat and unable to accommodate a sphere. In turn, without proper contact with the acetabulum, the femoral head and neck will not grow normally."
When treatment is required, the first choice for children under six months old is nonsurgical, using a Pavlik harness. In the minority of cases where this does not work, and in children not diagnosed until after six months of age, surgery may be required.
The Pavlik harness is a soft brace that gently redirects the head of the femur into the depth of the socket or acetabulum, which stimulates normal development of the joint.
Usually, the harness generally is used for three months. Initially, the child will wear the harness full-time and, as the hip position improves and stability is achieved, this can be reduced to part-time use. Treatment with the Pavlik harness is successful in about 85% of dislocated hips in children under six months of age.
Unfortunately, the Pavlik harness is not a good treatment option for older children because the hip has become more fixed in the dislocated position and is more difficult to realign.
For the small number of patients in whom treatment with the Pavlik harness is not successful, and for children in whom the diagnosis is not made until after they are six months old, the orthopedist may recommend either a closed reduction or open reduction surgery. Reduction is a procedure in which the bones are realigned or put back into place to optimize hip joint congruity. Reduction procedures are performed by pediatric orthopedists with specialized experience in the treatment of hip dysplasia. There are two types of reduction:
Following closed reduction of the hip, the patient is placed into a spica body cast for 12 weeks to maintain proper alignment of the hip ball and socket. At HSS, we use cross-sectional, 3D MRI imaging of the hip after closed reduction in order to confirm appropriate location of the hip and confirm hip joint congruency. HSS prefers to use MRI imaging, rather than X-rays or CT scans, since radiation is not involved.
Treatment by open reduction is generally reserved for children greater than 10 months of age who have new diagnosis of a dysplastic hip, or in cases in which a prior, closed reduction of the hip was unsuccessful.
In this procedure, the surgeon makes an incision, removes any obstacles to anatomic realignment of the hip (such as adjusting tight muscles or other soft tissue) and relocates the femoral head into the acetabulum. The surgeon may also need to restore normal anatomy by performing a hip osteotomy, a procedure in which cuts are made to the femur and/or the acetabulum in order to adjust the angles at which the bones meet and optimize joint congruity. The need for a femoral or acetabular osteotomy increases with the age at which diagnosis is made. It is usually required to correct abnormal development of the bones in any child over age three or four.
All reduction procedures, including those that involve an osteotomy, are done on an inpatient basis and require the use of general anesthesia. Children who undergo open reduction wear a cast for a period of six to eight weeks. Once the cast is removed, he or she usually continues to wear a brace at night until the orthopedic surgeon determines that the hip joint is developing normally.
In some patients who have an open or closed reduction and/or a femoral osteotomy, an osteotomy of the pelvis may also be required to adjust the angle of the acetabulum. In younger patients, the procedure often used is the Pemberton or Dega osteotomy, in which the bony and cartilage roof of the hip is reoriented into normal alignment.
The risks associated with surgery – bleeding, infection and those associated with anesthesia – are minimal. Pediatric orthopedists take special care to avoid a condition called avascular necrosis (also known as AVN or osteonecrosis), in which the bones of the hip joint do not receive enough blood. This can be caused if the femoral head (the ball of the hip joint) is put back into the acetabulum (socket) with unnecessary pressure, and so minimal pressure is used. Avascular necrosis can result in abnormal growth of the bone.
Regarding the safety of these procedures, Dr. Widmann says, "What I usually tell parents is that the primary risk with a diagnosis of developmental hip dysplasia is not doing anything at all. Untreated, these children face a high risk of developing osteoarthritis as adults, with the associated degenerative changes that cause chronic and progressive pain and stiffness."
Although the numbers are difficult to define, some members of the medical community believe that up to 50% of adults who eventually require hip replacement due to osteoarthritis, have developed the disease as a result of a pediatric hip problem. The majority of those cases are thought to be hip dysplasia.
The earlier the condition is treated, the better the chance of a successful outcome, meaning a hip that appears anatomically normal both during physical examination and on X-ray. Children who are treated for hip dysplasia are examined on regular intervals until they are skeletally mature (when growth is completed), to ensure that normal development continues. In some cases, a dislocated hip that was successfully reduced may still develop dysplasia in later years, requiring additional treatment.
Summary Prepared by Nancy Novick • Diagnostic imaging examinations provided by HSS Radiologists