All newborn babies have their hips checked within a few days of birth and at six weeks, because if a dislocation goes unnoticed the child will grow up with a short leg on one side and a painful limp, and get arthritis when older.

So, while congenital dislocation of the hip isn't a life-threatening problem - and babies are unlikely to experience pain because they're not putting any weight on the joint - it can have long-term complications if not treated early.

Joint problem

The hip is a ball-and-socket joint: the end of the leg bone (femur) forms a ball shape, which rolls around in a cup-shaped socket in the pelvic bones. This allows the leg to move through a large circle at the hip.

In new babies, the cup shape of the socket may be very shallow, allowing the ball of the femur to slip in and out of position.

More than one in 100 newborn babies has 'unstable' hips (which can be dislocated by the doctor during testing), but only one in ten of these is a true dislocation that requires more intensive treatment.

Girls are affected six times more often than boys and, rather strangely, the left hip is four times more likely to be affected than the right. In a third of cases, both hips are affected.

Possible long-term symptoms

Occasionally a dislocation is missed when babies are tested and x-rays aren't much help because at this age so much of the hip joint is made of cartilage instead of bone.

If tests don't pick up the problem, the dislocation can cause symptoms when the baby starts to walk. These may include:

• Delayed walking
• Abnormal waddling gait (the affected leg is shorter)
• Asymmetrical thigh creases (an extra crease on the affected side)
• Inability to abduct the affected hip fully (move the leg out away from the body)

Treatments

The recommended treatment of congenital dislocation of the hips depends on the extent of the dislocation and the shape of the hip socket.

Initial treatment consists simply of putting a baby in double nappies. This should keep the leg in the correct position to prevent dislocation, allowing normal growth of the cartilage of the socket.

The baby is then reassessed after three weeks. If there's still a problem, referral to a specialist orthopaedic surgeon will be needed. The specialist is likely to recommend a splint or plaster cast to hold the legs slightly open. This is worn for three months to allow the socket to grow into the right shape.

If the problem hasn't sorted itself out by about six months, more complex traction and splinting may be needed, and sometimes even an operation.

This article was last medically reviewed by Dr Trisha Macnair in March 2008