What Is Hip Dysplasia?
Hip dysplasia, also known as developmental dysplasia of the hip (DDH), is a condition where the ball and socket of the hip do not fit together correctly. The hip is known as a ball-and-socket joint; there is a ball at the top of the femur (thigh bone) that fits into a socket in the pelvis. For most people, the condition is present at birth. However, it can also develop after birth, which is why it is called developmental dysplasia of the hip.
When the hip ball and socket don’t fit together properly, it increases the risk of hip instability, which can lead to hip dislocation. Some cases are mild and do not cause symptoms until later in life. If the condition is noticed in infancy it is more easily corrected.
Causes and Risk Factors
The exact cause or causes of hip dysplasia are unknown. It is likely a combination of factors. Genetics plays a role—a person is roughly 12 times more likely to have the condition if there is a parent also had it.
Positioning in the womb can also increase a baby’s risk of developing hip dysplasia, especially if the birth was a breech, meaning that the baby was turned around in the mother’s womb and was positioned feet first. The hip dysplasia is more likely to occur on the left side than the right side.
Symptoms can vary based on the age of the person with DDH. In infants, symptoms can be limited to one leg seeming to be longer than the other or decreased range of motion in the hip. Once the child is old enough to walk, he or she may have a limp.
In adolescents and adults, hip dysplasia can lead to osteoarthritis or a hip labral tear due to improper and compromised walking mechanics. In normal hip anatomy, a pad of cartilage called the labrum helps to hold the femur head in the hip socket. With hip dysplasia, more pressure than normal is put on the labrum, increasing the risk of tears. Hip dislocation, where the femoral head comes out of the socket, is also a risk.
For infants, a physical exam is typically the diagnostic method used. The baby’s doctor will manipulate his or her legs in various directions, checking for any instability when placing some stress on the hip. For older patients, a physical exam and medical and family history can usually give a doctor the suspicion of hip dysplasia. However, imaging scans are often needed to confirm the diagnosis.
Hip ultrasound testing is a common and accurate way to diagnose the condition in newborns. The ultrasound will show the position of the ball in the socket and can also show hip instability which may be from early dysplasia.
An X-ray, especially for children older than three months of age, will show bone position and can detect if the head of the femur does not fit correctly into the hip socket or if the socket is not shaped correctly.
If X-rays are inconclusive, computed tomography (CT) scans can build a more complete picture of the hip anatomy. Magnetic resonance imaging (MRI) scans can help determine if osteoarthritis or damage to the labrum is present.
The earlier treatment begins, the easier it is to correct hip dysplasia. Infants’ bones are still soft and malleable. Babies under the age of six months can wear a brace, called a Pavlik Harness, which positions the femur’s head into the hip socket allowing the hip to stabilize and develop properly over a period of several months.
For older babies and young children, a doctor may need to set the femoral head into the hip socket and put the child in a cast to hold it in place, either by closed manipulation or, if necessary, by open reduction (a surgical method of alignment).
Older children and adults have surgical options to treat hip dysplasia. One possibility is known as a periacetabular osteotomy. A surgeon makes cuts in the pelvic bone around the hip socket (also known as the acetabulum) and repositions it so the socket and femur head fit together better. This procedure may be in conjunction with a proximal femur osteotomy to better fit the ball into the socket of the hip joint.
When there is longstanding dysplasia with associated osteoarthritis, a hip replacement may be necessary. Also known as hip arthroplasty, a hip replacement entails replacing the femoral head and the acetabulum with metal and plastic components.
Recovery from hip surgery like this can take six weeks to three months or more. Physical therapy to strengthen the leg muscles and return range of motion to the hip joint will be an important part of recovery.