Hip dysplasia refers to a condition where the relationship between the head of the femur (thigh bone) and the acetabulum (hip socket) does not develop properly. The hip may be totally dislocated (hip luxation), partially dislocated (hip subluxation) or just unstable or loose. It is normally present from birth and usually in the left hip only because the unborn child lies on its left side next to the mother's spine. Only 2% of cases have both joints affected.
The image above shows A) Normal hip B) Dyslpasia C) Subluxation D) Luxation
The condition affects 1- 3% of all newborns with 80% of cases being female.It is responsible for 29% of primary hip replacements in people up to 60 years of age.
There is no known cause for this condition but the following factors are all thought to play a role.
The newborn will not show signs of distress or pain.
All babies are given a thorough examination soon after birth and one of the conditions that doctor routinely looks for is hip dysplasia.
Checks include: -
If a problem is suspected than an ultrasound (see image right) may be taken (before 4-6 months of age) or an X-ray (over 4-6 months of age)
If the condition is not picked up at this stage it may be evidenced later if a child limps when they start to walk.
Many children will grow out of the condition without any intervention but as it is not possible to predict which, all children that raise concerns will be monitored.
The earlier treatment is started the better the outcome and the greater chance of avoiding long term damage such as osteoarthritis.
The aim of any treatment is to establish a good stable, contact between the femoral head and the acetabulum which should allow the joint to develop normally. This is done by keeping the hip in a flexed position for sufficient time.
If the condition is diagnosed early enough then a "nappy splint" may be used. If this isn't sufficient then the infant may need to wear a Pavlik harness for about six weeks full-time and a further six weeks part-time. The harness keeps the child's legs bent in the correct position. The harness works well solving the problem for 90% of children with milder hip dysplasia and 80% of those with a more severe problem.
One possible, though not common, complication of this method is avascular necrosis (loss of blood flow to the femoral head which may result in bone death.).
If the infant does not respond to these interventions or the condition is not diagnosed till later then surgical treatment may be needed to position the head of the femur correctly. Prior to surgery the child may be placed in traction to loosen the tissue around the joint. Following surgery a plaster cast, known as a hip spica, will be applied. This encloses both hips and keeps the legs apart and may be used for several months. This process is known as closed reduction.
An open reduction is usually carried out only on children over 2 years. This involves cutting any tendons, ligaments or muscle that is preventing the femur from fitting inside the acetabulum (the cup part of the joint). The hip joint can then be put in place. It is usual for the child to be put into a hip spica following surgery.
In some cases it may be necessary to perform an osteotomy. This involves cutting and rotating the femur so that it is in the best position for a snug fit with the acetabulum. With some older children it may be necessary to also alter the positioning of the acetabulum.
All children who undergo surgery for hip dysplasia are at increased risk of developing osteoarthritis during their 40s and 50s.
More information on hip dysplasia is available at the International Hip Dysplasia Institute
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