It used to be called ‘Congenital Dislocation of the Hip’ (CDH). Nowadays it is now called ‘Developmental Dysplasia of the Hip’ (DDH), because we realise there are some babies who examine normally at birth, but over the early months of life develop an abnormal hip joint, whose socket becomes flattened and unstable. This latter group is caused by an inborn genetic factor or inappropriate posturing of the legs over the first months (See last paragraph).
For the first year a baby’s hip joint is mostly made of cartilage, which is mouldable. Beyond one year of age it turns to bone, which is not. We therefore wish to diagnose dysplasia while the joint is still cartilage so treatment can fix it completely. If treatment is delayed until after the joint turns to bone such treatment is never completely satisfactory. The joint usually remains abnormal and the patient may end up with a limp or, at the least, develop early osteoarthritis requiring a hip replacement in early adult life.
It’s an problem that can develop as babies’ hips mature, the hip joint socket is meant to deepen in the first year or so, as it also turns to bone (from being soft cartilage). The deepening process is on-going and it can be interfered with.
There is a suggestions that that is happening from tight sleeping bags where the baby’s legs are extended out and wrapped firmly over these months. Swaddling is OK as long as the hips are FLEXED; and babies prefer that flexed posture too – as it reminds them of their position in the womb.
So: If your baby has used one of those bags or there’s been tight swaddling with stretched out legs: see your doctor for a hip check on the baby. It can be sorted out as long as it’s picked up in the first year- and the sooner the better.