Causes of DDH

What causes Hip Dysplasia?

The exact cause(s) are not known. However it is widely believed that hip dysplasia is developmental. This is because hip dysplasia is known to develop around the time of birth, after birth, or even during childhood. This is also why hip dysplasia is often referred to as developmental dysplasia of the hip (DDH).

It is currently believed that infants are prone to hip dysplasia for the following reasons:

Hip dysplasia is approximately 30 times more likely when there is a family history.

Genetics plays a role, but is not a direct cause of hip dysplasia.

  • If a child has DDH, the risk of another child having it is 6% ( 1 in 17 )
  • If a parent has DDH, the risk of a child having it is 12% ( 1 in 8 )
  • If a parent and a child have DDH, the risk of a subsequent child having DDH is 36% ( 1 in 3 )

This means that up to 1 out of 10 newborn infants will have some hip instability if a parent or sibling already has hip dysplasia.

 

The baby’s womb position can increase pressure on the hips

The positioning of the baby in the womb can cause more pressure on the hip joints, stretching the ligaments. It’s thought that babies in a normal position in the womb have more stress on the left hip than on the right hip. This may be why the left hip tends to be more affected.

Babies in the breech position are more likely to have hip instability than babies in a normal womb position.

Normal womb position.  Not normally any risk for hip dysplasia / DDH

Normal womb position.

Breech womb position. A risk factor for hip dysplasia or DDH

Breech womb position.

Babies with fixed foot deformity or stiffness in the neck (torticollis) have slightly increased risk of hip dysplasia. This may partly be due to limited space in the womb from these deformities.

Also, around the time of birth, the mother makes hormones that allow the mother’s ligaments to become lax (stretch easier) so that the baby can pass through the birth canal.

Some infants may be more sensitive to these hormones than others, allowing for excessive ligament laxity in the baby. Girls usually have more ligament laxity than boys and girls are 4-5 times more likely to have hip dysplasia than boys.

 

The bones of an infants hip joint are much softer than an adult hip joint

It is easier for an infant’s hip to become misaligned (subluxate) or dislocate than an adult hip. This is because an infant hip socket is mostly soft, pliable, cartilage. Whereas an adult’s hip socket is hard bone.

Child
A baby's hip joint is mostly soft cartiledge (grey).
Illustration of an infant hip joint that’s still developing. The brown areas represent dense bone, where the grey areas represent soft, pliable cartiledge.
Adult
An adult hip joint is mostly hard bone (brown)
Illustration representing an adult hip joint. Note how the grey areas that were present in the infant joint are now completely replaced by hard bone.

 

Infant positioning during the first year of life

Cultures that keep infants’ hips extended on a cradleboard or papoose board have high rates of hip dysplasia in their children. Cultures that hold infants with the hips apart have very low rates of hip dysplasia. For this reason, swaddling with the hips extended during the first few months after birth should be avoided, and a hip-safe method should be used.

Babies carried in a sling on the back with hips spread is helpful against hip dysplasia.

Picture of a mom carrying her child in a back sling. Her babies hips remain spread (wrapped around her mother’s back) keeping the hips is a safe position.

Cradle boards and tight swaddling may make hip dysplasia worse.

Picture showing how a papoose board (or cradleboard) is used. The child’s legs are kept close together, extended, and tied down tightly by the wrap on the board.

 

A historical perspective

For additional background information on causes of hip dysplasia, the IHDI has made the following, long-lost, feature-length video about a study done for hip dysplasia in Saskatchewan Indians


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