Developmental Dysplasia of the Hip
Healthy Hips Week!
April 23rd-29th is Healthy Hips Week for Hip Dysplasia. So what better time to write about this common childhood condition!
More information available over at Healthy Hips Australia.
Developmental dysplasia of the hip (DDH) refers to abnormal development of the hip joint in a newborn baby, which results in the joint either being dislocated or prone to dislocation. It is a relatively common condition with approximately 1 in 600 girls and 1 in 3000 boys affected.
Before we can understand what DDH is and why it occurs, it is important to understand the anatomy of the hip joint.
Hip Joint Anatomy
The hip joint is a ball and socket joint. The ball is formed by the femoral head, which is the top of the femur (thigh bone). The ball fits into the hollowed-out socket of the pelvic girdle, known as the acetabulum, and together, they create the hip joint. The ball is usually anchored tightly into the socket and held in place by surrounding ligaments and joint capsule.
Normal Hip Joint. Image courtesy of Bacher Tai Chi.
In a baby with DDH, the socket is abnormally shallow, meaning that the femoral head cannot fit firmly into the socket. Sometimes, the ligaments that help to hold the joint in place are stretched or loose and may also allow the femoral head to slip out of the joint. DDH has a wide range of severity and the degree of hip laxity or instability can vary greatly.
Severity and Types of DDH
Hip dysplasia has a wide range of severity, and the degree of hip looseness or instability can vary greatly amongst children diagnosed with DDH. In some cases, it is simply that the ligaments surrounding the hip joint are loose, allowing the hip to subluxate. In other cases, the ball is slightly or completely dislocated from the socket.
DDH is usually classified into 3 different categories – subluxatable, dislocatable and dislocated.
- Subluxatable: These are the mildest cases of DDH. In these cases, the head of femur is loose in the socket due to the ligaments surrounding the joint being loose or stretched. During a physical examination, the bone can be moved within the socket, but will not dislocate.
- Dislocatable: These are moderate cases of DDH. In these cases, the head of femur lies within the acetabulum, but during a physical examination it can easily be pushed out of the socket.
- Dislocated: These are the most severe cases of DDH. In these cases, the head of femur is completely out of the socket.
Hip Dysplasia Categories. Image courtesy of Canadian Orthopaedic Foundation.
Causes of DDH
There are many causes of DDH, some of which are genetic and some which are environmental. DDH is more common in girls and first born children. Other causes of DDH include:
- family history – around 1/3 of babies with DDH have a relative who also had the condition
- breech delivery – being born bottom first or feet first can put significant stress on the baby’s hip joints
- congenital disorders (e.g. Cerebral Palsy or Spina Bifida)
- multiple babies – due to lack of space inside the womb
The hormone Relaxin which is secreted by pregnant women to allow their ligaments to relax to help delivery of the baby through the mother’s pelvis can also contribute to DDH. Some of these hormones also enter the baby’s blood via the placenta and can make the baby’s ligaments relax, resulting in the hip joint being loose in the socket.
Signs and Symptoms of DDH
- reduced joint mobility or stiffness of the hip joint
- different leg lengths
- the child’s leg may turn outward on the affected side
- the child may lean to the affected side when standing
- the skin creases on their bottom or legs may be uneven or asymmetrical
Babies are routinely checked at birth to make sure their hip joints are in the correct position, and are followed up by regular checks during routine appointments with their Maternal and Child Health Nurses. Your treating practitioner will use specific tests to determine if the hip can be dislocated and/or put back into proper position. If an abnormality is detected, a referral will be made for an ultrasound or x-ray, which can create detailed images of the hip joints to confirm the diagnosis and determine the extent of the dislocation.
Treatment methods for DDH vary according to the child’s age and the severity of their condition. When DDH is detected at birth or within the first 6 months of a child’s life, it can usually be corrected with the use of a harness or brace. If the hip is not dislocated at birth, or is not discovered until later, treatment becomes more complicated with less predictable outcomes. Therefore, it is important to check for and treat DDH as early as possible.
Babies with DDH can be successfully treated with a splint. The baby is placed in a soft splint called a Pavlik Harness. The splint holds the hip joint in the correct position, while allowing free movement of the legs and easy nappy care, so that the ligaments around the hip joint can tighten up and to promote normal formation of the hip socket. The baby may wear the splint for several months until the hip joint is stable and x-rays are normal.
1 – 6 Months
Like treatment for newborns, a harness or splint is used to reposition the thigh bone in the socket. Even with hips that are initially dislocated, this treatment method is usually successful. If splinting does not work, the child may need to undergo a procedure known as a closed reduction, where the hip joint is gently moved into the correct position while the child is under anaesthetic. Following this procedure, the child will need to wear a plaster cast known as a hip spica to hold the bones in the correct position. A hip spica covers the child’s body from the knees to the waist and may need to be worn for a few months.
6 months – 2 years
Children between these ages are also treated with closed reduction and hip spica. In most cases, skin traction is used prior to undergoing the closed reduction to prepare the soft tissues around the hip joint for the change in bone positioning.
Treatment of Hip Dysplasia with a Pavlik Harness. Image courtesy My Hipster Bub.
If the above treatments are unsuccessful or if DDH is diagnosed late, open surgery or an open reduction is required. In this procedure, while the child is asleep under anaesthetic, a small incision is made in the groin that allows the surgeon to see the bones and soft tissues. The hip joint is then moved into the correct position and the joint is made more stable by surgery to surrounding tendons. Following surgery, the child will then need to wear a hip spica to keep the joint in the correct position while the tissues heal.
In some cases when DDH is diagnosed late, more surgery known as osteotomy may need to be done to the pelvic or thigh bones to reshape them make sure the hip joint stays in place. Again, a hip spica will be used following surgery to help the joint remain in the correct position.
Following treatment for DDH, regular follow up monitoring and x-rays are required until the child’s growth is complete. If diagnosed early and treated successfully, children with DDH are able to develop a normal hip joint and should not have any functional limitations. In some cases, even with appropriate treatment, hip deformity and osteoarthritis may develop later in life, however this is more of a concern when treatment begins after the age of 2 years.
If you have any concerns that your child may be suffering from DDH, be sure to seek the advice of your doctor or physiotherapist.
And remember, this week is Healthy Hips Week. For more information, visit Healthy Hips Australia.