Developmental dysplasia of the hip (DDH), also known as developmental pediatric dysplasia of the hip or hip dysplasia, is the term used to describe a range of hip joint abnormalities. Hip dysplasia may develop in a baby around the time of birth or during early childhood. Although it is most commonly diagnosed in babies and young children, DDH can also affect adolescents and adults. This can usually be attributed, however, to milder cases of DDH that went undiagnosed or untreated when the patient was a child.
In the healthy hip joint, the upper end of the femur (thighbone) meets the acetabulum to fit together like a ball and cup, in which the ball rotates freely in the cup. Cartilage, a smooth protective tissue, lines the bones and reduces friction between the surfaces during movement.
In DDH, however, one or more of these functions work incorrectly. The conditions encompassed by the term hip dysplasia include:
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.
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. The risk of hip dislocation at birth is approximately one in one thousand. If a parent experienced hip dysplasia during childhood, the risk of his or her own child developing it increases by 12% compared with 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.
Other influences during pregnancy and birth include:
When developmental hip dysplasia is present at birth, the abnormality may be detected during a routine physical examination of the newborn. During this examination, the physician gently flexes the child's hips in different directions. If the hip is dislocated or can be easily dislocated or subluxatated (partially dislocated), the doctor she 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. 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, the orthopedist uses an ultrasound. This technology offers a significant advantage over conventional X-rays because images may be taken with the hip 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.
In order to ensure proper development of the bones that make up the hip joint, early intervention is essential and may be nonsurgical. "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 cup, providing a specific growth stimulus, the cup 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."
For patients up to six months of age, the first choice of treatment for hip dysplasia, is the use of the Pavlik harness, a soft brace that gently redirects the head of the femur into the depth of the socket or acetabulum, stimulating normal development of the joint.
The harness is generally used for three months total, initially full-time and as the hip position improves and stability is achieved, part-time harness treatment may be instituted. Treatment with the Pavlik harness is successful in about 85% of dislocated hips in children under six months of age.
For the small number of patients in whom treatment with the 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 closed or open reduction. Reduction is a procedure in which the bones are realigned, or put back into place. Unfortunately, the Pavlik harness is not a good treatment option for older children because by then the hip has become more fixed in the dislocated position and is less easily realigned. Reduction procedures are performed by pediatric orthopedists with specialized experience in the treatment of hip dysplasia.
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 and acetabulum. It is mandatory that cross-sectional imaging of the hip be performed after closed reduction in order to confirm appropriate location of the hip. Current imaging modality of choice at HSS is MRI, since radiation is not involved.
Treatment by open reduction is generally reserved for children between 18 months and two years 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 proper 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 or the acetabulum. The need for an 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 include osteotomy, are done on an in-patient basis and require the use of a general anesthetic. 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 such time that the orthopedist has determined that normal hip development is proceeding.
Pelvic osteotomy and reorientation of the acetabulum is occasionally necessary in the setting of residual hip dysplasia after open or closed reduction of the hip. In younger patients the procedure of choice is often the 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 do take special care to avoid a condition called avascular necrosis (AVN) in which the femoral head (the ball of the hip joint) does not receive enough blood, a condition that 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 an undiagnosed pediatric hip problem. The majority of those cases are thought to be residual undiagnosed hip dysplasia.
As discussed above, the earlier the condition is treated, the better the chance of a successful outcome: 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