This condition, which also goes by the name of Congenital Dislocation Of The Hip (CDH) and Hip Dysplasia, describes a spectrum of disease due to failure of normal formation of the hip.
This can range from a hip that is subluxatable (unstable when stressed) due to slight shallowness of the hip socket, to one that is completely dislocated. The term CDH implied that the hip was dislocated at birth in these children, but this term has been replaced by DDH as the hip can be in joint at birth but gradually move out of the joint with time if the condition is not diagnosed promptly and treated early.
What causes DDH?
The exact cause of DDH is unknown, but research has discovered several theories and risk factors for hip dysplasia. In the general population, the overall incidence of DDH is approximately 3-4 per 1,000 live births. There is often a genetic component, or familial tendency. Anything that causes cramping or crowding of the foetus inside the uterus (large birth weight, oligohydramnios: decreased amniotic fluid) is thought to cause an increased incidence of DDH. More significant risk factors for DDH include female gender, first born babies, babies born in the breech position (especially with feet up by the shoulders) and family history. Hip dysplasia is approximately 5 times more common in females than males. In addition, DDH affects the left hip more often than the right hip (approximately 60% affect only left hip, 20% only right hip, and 20% are bilateral.) Finally, there is felt to be a slightly higher incidence of DDH when other orthopaedic (torticollis, metatarsus adductus, clubfoot) or connective tissue disorders (Larsen syndrome) are present
Screening for DDH
Every newborn child has a hip examination just after birth before leaving hospital. There should also be a clinical examination at about 6 weeks performed by the GP.
Unfortunately, clinical examination, even in the best hands, can only detect those hips that are dislocated or very unstable. It does not exclude dysplasia which can then lead to dislocation at a later date. This is why hip ultrasound is by far the best diagnostic test and this should be combined with expert clinical examination.
In an older child, it may be possible to see a difference in leg lengths if a hip is dislocated. This will be combined with a decrease in hip abduction (movement of the hip to the side) and by the time the child is walking then there will be an obvious limp present.
Once the diagnosis if DDH has been made, the treatment will depend on the age of the child and the degree of instability. If the ultrasound shows that the hip is subluxating, dislocated, or that the acetabulum is shallow (decreased femoral head coverage), the initial treatment may consist of a Pavlik harness. The Pavlik harness is often used as the initial treatment of hip dysplasia in infants. It is a soft dynamic brace that maintains the hip in flexion (knee up towards the head) and abduction (knee away from the centerline). This position maintains the proper position of the femoral head and allows for “tightening up” of the ligamentous structures as well as for stimulation of normal formation and deepening of the hip socket.
The Pavlik harness is successful in approximately 90-95% of infants with hip dysplasia. The Pavlik harness is usually needed for approximately 6-12weeks, as long as there is continued improvement seen on serial hip ultrasounds.It needs to be worn for the whole day and night with only time out for bathing and dressing. After this 12 week period it may be needed at night time for up to a further 6 weeks. If there is no improvement seen, the Pavlik harness will be discontinued, and it will be necessary to proceed with closed reduction and spica body casting (done in the operating room). Pavlik harnesses are ordinarily the first line of treatment for DDH in newborns and infants under six months of age.
What happens if the Pavlik Harness does not work or the child is older than 6 months?
Occasionally in the young baby with prompt diagnosis of DDH, the harness will not work. This tends to be in very unstable hips that are completely dislocated. If this occurs the child will require a general anaesthetic to assess the hip. An arthrogram will be performed, which is a procedure where some dye is put into the hip to gather more information about whether there may be structures stopping the hip reducing into the joint properly. A closed reduction is attempted and if this is successful, then a hip spica is applied. The child will then spend 6 weeks in this plaster, followed by a further period of 6 weeks in broomstick plasters or splint, depending on age.
Hip spica treatment
The older the child at diagnosis, the higher the chance of requiring open surgery to reduce the hip. This also requires plaster treatment afterwards and is clearly associated with a longer rehabilitation. There is no doubt that the longer the hip is out of joint, the more difficult and extensive the treatment is, and the chances of obtaining a normal hip in adulthood are reduced. This is why hip screening is so important to try and reduce the incidence of children presenting with late dislocations.