Developmental dysplasia of the hip
Many conditions can affect a baby’s hip. Developmental dysplasia of the hip (DDH) is the only common condition but still only affects 1 to 3 babies per thousand (in the UK). It is common enough and serious enough for there to be a national screening programme for it. All babies therefore have a hip examination within a day or two of birth. Careful examination at that age can detect it on most occasions.
The hip is a ball-and-socket joint. The socket is called the acetabulum; the ball is called the femoral head, or head of the femur (thigh bone). Dysplasia means in this context that the hip socket has grown out of shape while the baby is still in the mother’s womb; it is not deep enough to hold the ball and this makes it unstable. In other words the ball fits only loosely in the socket. This results in a fairly wide variety of situations, depending on how shallow the socket is, how well the muscles and ligaments hold the joint, the position of the leg in the womb and a host of other factors, some of which are probably not even known. It is not a condition that is fully understood.
If the ball is completely out of the socket at birth it is called Congenital Dislocation of the Hip (CDH). Examination at birth usually reveals a reduced range of movement (abduction) which increases as the hip is reduced (ie the ball is “reduced” into the socket). This is very characteristic and is the test described by Ortolani. It should not be confused with the click that is often felt when examining a baby’s normal hip. “Clicky hip” is not a medical term and is not helpful. A dislocated hip needs to be treated as soon as practical (see below).
More often, the hip is not dislocated. The dysplasia might then be detected by gently testing its stability. This is the Barlow test. Instability can be detected in a large proportion of hips at birth, but most will stabilise on their own within 4 to 6 weeks. It is those that do not stabilise that have DDH. The Barlow test becomes much less effective within a few weeks of birth so we need another test to find out which babies still have DDH and therefore need treatment.
Fortunately ultrasound scans of the hip are very good at detecting dysplasia, if performed correctly. All children who have instability on the Barlow test at birth should therefore have an ultrasound scan at 4 to 6 weeks of age.
Why not scan all babies at birth with ultrasound?
Although better than the Barlow test, ultrasound cannot tell for sure which babies will get better without treatment. Scanning all babies at birth has therefore historically resulted in some over treatment. Most treatment does not harm the hip or the baby so treating all babies based on examination at birth (Barlow or ultrasound) has been advocated in some places with good results.
In most parts of the UK babies are examined on day one after birth without ultrasound. If there is instability, they are referred for an ultrasound at 4 to 6 weeks of age. Other babies have an ultrasound regardless of the presence or absence of instability; these are the babies with “risk factors”. In some countries and some parts of the UK all babies do have scans, but they are usually performed after a few weeks of age.
Risk Factors for DDH
Family history of DDH (especially a parent or sibling)
Breech presentation at term.
Oligohydramnios (lack of amniotic fluid)
Some foot and neck disorders, notably metatarsus adductus and torticollis
Syndromes and other specific diagnoses such as spina bifida and Ehlers-Danlos syndrome.
If the hip is found to be dislocated at the day one baby check, it is treated straight away, or as soon as practical; there is no need to wait for an ultrasound scan. Most hospitals in the UK use the Pavlik Harness. There are other harnesses or braces in use, particularly on the Continent.
The harness is also used to treat dysplastic hips (without dislocation) once the diagnosis is more certain, ie from 4 to 6 weeks of age, or as soon as the diagnosis is made. Babies over 6 months of age usually too strong for the harness, and a brace may be more useful.
We use the harness until the hip is normal or the harness has clearly not worked. We can tell within 2 weeks whether the harness has reduced a dislocated hip. If it has worked, I recommend a minimum treatment of 6 weeks. Most parents are keen to discard the harness but keeping the baby in for another couple of weeks after the ultrasound and examination are normal is reassuring for everyone.
The Pavlik harness nearly always works for dysplasia, but up to half of babies with dislocated hips need more treatment.
The details of the further treatment not only vary between children but also between surgeons and hospitals. The most important principle is that the hip is not harmed by the treatment. This may seem obvious but it is one of the commonest complications. Fortunately most of the adverse consequences of treatment are very minor and are unquestionably better than having no treatment. In my own practice, probably 5% of babies develop some evidence of growth disturbance after treatment. I say probably because subtle changes are difficult to measure objectively. There have been no serious consequences.
Without wishing to over-simplify, my method for CDH is as follows:
1. Non-walking child (usually an infant)
Stable reduction under anaesthetic at less than 45 degrees of abduction –> hip spica in 100 degrees of flexion and a little rotation.
Stable reduction only at more than 45 degrees of abduction -> proceed to open reduction by the medial approach if already 6 months of age or over, otherwise delay until old enough.
2. If already walking, perform an anterior open reduction with femoral shortening and add a pelvic osteotomy if needed. It is usually needed for the child over 2 years of age.
For the non-walking child, stability is achieved by growth of the acetabulum over a 6 month period, during which time the baby is in a hip spica and then a brace.
For the walking child, stability is achieved during the operation and the spica is used while the bones heal. This usually takes 6 weeks but a little extra may be needed depending on just how stable the hip is and how old the child is. The child is allowed to walk when the cast comes off.
After a child has been in a cast, even for only 6 weeks, the hip can be quite stiff and the muscles and bones will be weak. Careful supervision of the child is needed therefore during the first 2 weeks. The child will continue to limp for many months because of this. Older children are also likely to have a leg length difference which will usually resolve within 2 years, but may persist and require treatment. Often the treated side grows longer instead.
Parents worry about leg length difference, but it is best not to be concerned about it, and reassurance is all that should be needed. It is a harmless problem in the context of DDH and simple to deal with if necessary; and as the child is coming for follow-up for the hip anyway, the limb length can be measured and monitored at the same time.
Children who have had treatment for a dislocated hip should see the surgeon initially every 3 or 6 months and then annually until skeletal maturity. More surgery may be needed during this time. Skeletal maturity can be seen on the x-rays, but usually it occurs at 14 for girls and 16 for boys.
Babies who have been in a Pavlik harness for dysplasia (without dislocation) can be discharged once the x-ray is normal; this x-ray is usually taken at age 6 to 12 months.
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