Hip dysplasia is a relatively common condition that affects newborns and infants, impacting the development of the hip joint.
Also known as developmental dysplasia of the hip (DDH), it occurs when the hip joint fails to develop properly. This condition can range from mild instability to a complete dislocation of the hip joint.
Early diagnosis and treatment are crucial for ensuring proper development and preventing long-term complications. In this article, we will explore the causes, symptoms, diagnosis methods, treatment options, and address frequently asked questions related to hip dysplasia in babies.
Anatomy of the hip joint:
The hip is a ball-and-socket joint where the rounded projection, or ball, at the end of the femur (thigh bone) fits into the hip socket, known as the acetabulum. Ligaments, strong connective tissues, firmly anchor the ball into the socket, ensuring stability.
Newborns often have physiologic laxity of the hip and immaturity of the acetabulum during the first few weeks of life. In most cases, the laxity resolves, and the acetabulum proceeds to develop normally.
What is hip dysplasia:
Developmental dysplasia of the hip (DDH) affects the hip joint in babies and young children. It occurs when the socket is abnormally shallow and doesn't fully cover the ball portion of the upper femur bone.
In this situation, the ball is unstable within the socket and can vary from mild instability to a complete dislocation when the ball comes completely out of the socket.
Usually, only one hip is affected, most commonly the left hip but sometimes both hips are affected.
The term Developmental Dysplasia of the Hip is the preferred term since the condition is not always present or identifiable at birth and develops in the weeks or months after birth.
Hip dysplasia isn’t painful in babies but if left untreated, can cause irreversible damage that will cause pain and loss of function later in life.
Above is a photo presenting a comparison of two images side by side. On the left is an illustration depicting the anatomy of a normal hip, while on the right is an image showing a left hip dislocation, revealing a shallow acetabulum.
How common is it:
Estimates of the incidence of DDH are quite variable and depend upon the means of detection, age of the child and the criteria used for the diagnosis.
Historically, the incidence of DDH with dislocation was thought to be 1 to 2 per 1000 children [1].
It is now estimated that dislocatable hips and hips with severe or persistent dysplasia occur in 3 to 5 per 1000 children [2].
Mild hip instability is more common in newborns, with reported incidence as high as 40 percent. However, mild instability or mild hip dysplasia in the newborn period often resolve without treatment [3].
In South Australia, where DDH is notifiable to the South Australian Birth Defects Register, the incidence is around seven per 1000 live births [4]. For children born in 2003–2009, 11.5% of cases were a late diagnosis after three months of age [4].
Causes and risk factors of Hip Dysplasia:
Hip dysplasia in infants can result from a combination of environmental and genetic factors [5]. Risk factors for developmental dysplasia of the hip (DDH) include:
1. Family history of DDH: Due to genetic predisposition, babies born into families with a history of hip dysplasia are at a higher risk of developing the condition. In a large review, the risk of hip dysplasia in subsequent children was 6 percent when there was one affected child, 12 percent when there was one affected parent, and 36 percent when there was an affected parent and an affected child [6].
2. Females: Hip dysplasia is two to three times more common in female than in male infants [7] and in some studies girls are 4-5 times more likely to have hip dysplasia than boys. The increased incidence in females has been attributed to a transient increase in ligamentous laxity related to increased susceptibility of female infants to the maternal hormone Relaxin, a hormone that readies the mother's body for childbirth by causing relaxation and loosening of the muscles and ligaments in her pelvic region.
3. Position in the Womb: Certain positions in the womb can increase the risk of hip dysplasia by causing more pressure on the hip joint.
- Breech position is the greatest single risk factor for hip dysplasia with an incidence as high as 12 percent in breech females and 3 percent in breech males [8].
- Oligohydramnios (low amniotic fluid in the womb) [9].
- Babies with conditions such as clubfoot, metatarsus adductus (inward turning of the front half of the foot), or torticollis (stiff neck) have a slightly higher risk of hip dysplasia.
- It is worth noting that being a twin or triplet does not constitute a risk factor for DDH [10]. Additionally, having a large baby does not significantly increase the risk of hip dysplasia [11].
4. Firstborn children.
5. Hormonal Factors: 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 thus leading to hip dysplasia.
6. Underlying neuromuscular disorders such as cerebral palsy.
7. Incorrect positioning of the baby's hips during the first few months of life can increase the risk of hip dysplasia. Swaddling the legs tightly together or prolonged positioning in a baby carrier that does not support the hips properly may hinder normal hip joint development. To promote hip health during swaddling, it is crucial to provide babies with ample space for leg movement, allowing for proper bending of the hips and knees. Please refer to the information below for more details.
Diagnosing Hip Dysplasia:
The diagnosis of hip dysplasia in infants can be challenging due to the potential variation in signs and symptoms. While some cases may not exhibit any noticeable findings, early detection remains crucial for effective management and treatment.
To diagnose hip dysplasia, healthcare professionals use a combination of physical examination techniques and imaging tests.
During a physical examination, the healthcare provider will assess the baby's hip stability, range of motion, and check for any noticeable abnormalities.
Here are the key examination findings commonly observed:
- Hip instability: During the newborn physical examination, paediatricians, and midwives, assess hip stability by performing specific manoeuvres such as the "Barlow" and "Ortolani" tests. These manoeuvres aim to identify any instability in the hip joint by feeling for a palpable “clunk”.
- Limited range of motion: During nappy changes, you may notice that one hip does not move outward as freely as the other side or both hips appear stiff with restricted outward motion.
- Asymmetry in leg length: One leg may appear shorter than the other, particularly noticeable when the baby is lying on their back with their hips and knees bent at a 90° angle.
- Uneven Skin Folds: An asymmetrical appearance of the skin folds around the thigh or buttock area may indicate hip dysplasia.
- Preferring one side while crawling: The infant may exhibit a preference for crawling with one side of their body, avoiding putting weight on the affected hip.
- Abnormal walking or gait: The baby may limp, lean to the affected side, or walk with the leg turned outward.
Diagnostic imaging
Imaging is conducted to confirm or exclude the diagnosis of hip dysplasia. Ultrasonography is generally preferred for infants younger than six months of age, while X-rays are typically used for infants older than six months.
Ultrasound: An ultrasound study is performed in young infants when hip dysplasia is suspected. This examination is crucial for confirming the diagnosis or ensuring that the hip joint is normal. Ultrasound provides information about the position of the femoral head (ball), the degree of acetabular (hip socket) coverage (how much of the ball is covered by the socket), and the stability of the joint.
Ultrasound is a safe, non-invasive imaging method that does not involve radiation.
During the examination, certain angles are measured, with the alpha angle being the most commonly used to guide treatment.
A normal alpha angle is considered to be more than 60 degrees. Mild dysplasia is present when the alpha angle ranges from 43 to 60 degrees, while severe dysplasia occurs when the alpha angle is less than 43 degrees.
Additionally, the ultrasound examination assesses the stability of the hip by capturing images that demonstrate the extent to which the hip moves out of the socket. Generally, stability is indicated when more than 50% of the ball remains within the socket. Any percentage lower than this suggests instability. It is important to note that hip instability, often observed in newborns, tends to resolve by six to eight weeks as the ligaments naturally tighten with age.
X-rays: The predominantly cartilaginous nature of the bones make x-rays an unsuitable means of assessing structure in the first few months after birth.
Therefore, their usage is generally reserved for children older than six months. X-rays provide a detailed view of the hip joint and can be valuable in determining the most appropriate treatment approach.
Treatment Options
The treatment for hip dysplasia in babies depends on the severity of the condition and the age of the child. Early detection and intervention significantly improve the chances of successful treatment.
The following are common treatment approaches:
Pavlik Harness:
For infants under six months old, the Pavlik harness is often recommended as the initial treatment approach. This soft brace helps maintain the hips in the correct position (‘frog leg’ position), promoting proper development while allowing some degree of movement.
This ensures that the ‘ball’ part of the hip joint is held deeply into the ‘cup’ part, encouraging growth in the correct areas.
Other doctors might recommend using the Denis Browne Hip Abduction Brace which is also designed to maintain the legs in a ‘frog leg’ position.
Initially, the harness is typically worn for 23-24 hours a day. The duration of treatment varies and will be determined by your doctor based on the severity of the dysplasia. In most cases, the harness is worn for a period of 12 weeks, with the possibility of a longer duration depending on the hip's response to treatment and the severity of the condition. Even after that, the baby may need to continue sleeping at night in the Pavlik harness or the Rhino Hip Abduction Brace for a few weeks as a precautionary measure.
Closed Reduction:
In cases where the Pavlik harness is ineffective or if the hip dysplasia is diagnosed after the six-month mark, a closed reduction may be necessary.
Closed reduction refers to the process of repairing the hip joint without the need for surgery. This procedure involves manually repositioning the hip joint while your child is asleep under anaesthetic and placing the child in a spica cast to maintain the proper alignment during healing.
A spica cast is a plaster cast that immobilizes both hips and covers the patient from approximately the nipple line and down to the ankles.
Open Reduction:
In severe or late-diagnosed cases, open reduction surgery may be required. The surgeon repositions the hip joint surgically and may use pins, screws, or plates to stabilize it. Following the surgery, a spica cast is applied to protect the hip joint during the healing process.
Ongoing Monitoring:
Regardless of the treatment method used, regular follow-up appointments and monitoring are crucial to ensure that the hip joint develops properly and remains stable. This may involve periodic imaging tests and assessments to track the progress of the treatment.
Outcome:
When diagnosed early and treated successfully, children with DDH have the ability to develop a normal hip joint and experience no limitations in terms of function. However, if left untreated, DDH can result in pain and osteoarthritis during early adulthood. Additionally, it may lead to leg length discrepancy or reduced agility.
Conclusion
Hip dysplasia is a common condition affecting babies' hip joint development. Timely diagnosis and appropriate treatment are essential to promote optimal hip joint formation and function. Various factors, including genetics, environment, hormonal imbalances, and improper positioning, can contribute to the development of hip dysplasia. Identifying symptoms, such as limited range of motion, leg asymmetry and uneven skin folds and obtaining an accurate diagnosis through physical examination and imaging techniques, are critical for effective management. Treatment options range from non-invasive methods like the Pavlik harness to surgical interventions such as closed or open reduction. Ongoing monitoring is necessary to ensure the long-term stability and health of the hip joint. By increasing awareness and understanding, we can all play a crucial role in early detection and treatment, enabling babies with hip dysplasia to lead healthy active lives.
Commonly asked questions:
Is my baby's hip dysplasia causing them pain?
No – hip dysplasia does not typically cause pain in babies.
Does a hip click indicate that my baby has hip dysplasia?
No, a hip click does not necessarily indicate hip dysplasia. The clicking sound can occur due to various reasons, such as ligament movement, as the baby's hip joint develops. However, if you do hear a click, you should have your baby checked by a health care provider.
What can I do to prevent hip dysplasia?
Firstly, make sure to consult with your paediatrician or midwife to determine if a screening hip ultrasound is needed based on the physical examination or any risk factors.
When swaddling your baby, choose swaddles that do not restrict leg movement and allow the legs to freely bend up and out at the hips.
When using a baby carrier in the first few months, ensure that your baby is facing you and that their thighs are spread around your torso, with hips bent and knees slightly higher than the buttocks. This position, known as the 'M'-position or 'frog leg' position, generates beneficial forces for optimal hip development.
My baby had their six-week hip ultrasound, which showed mild to moderate hip dysplasia. Our doctor wants us to repeat the ultrasound in 4-6 weeks. What can I do in the meantime to help my baby?
Firstly, it's important to follow the recommendations provided in the previous answer. In addition, performing gentle stretching exercises can be beneficial for your baby. While your baby is lying on their back, try gently spreading their thighs while their knees are bent and keeping them spread out for 1 minute, if tolerated. However, it is crucial to consult with your healthcare provider or a specialist to ensure you're performing the exercises correctly. These measures can contribute to promoting healthy hip development during this period.
Can my baby have ‘tummy time’ if hip dysplasia is suspected while waiting for a hip ultrasound?
Yes, it is safe for your baby to have 'tummy time' even if hip dysplasia is suspected. It is especially beneficial if your baby maintains a frog position during tummy time. However, please remember to only allow tummy time when your baby is awake to ensure their safety.
Does it help to wear double or triple nappies to prevent hip dysplasia?
Short answer- probably not! Wearing double or triple nappies is a practice that is sometimes recommended by health professionals to help maintain proper hip position and prevent hip dysplasia. However, the effectiveness of this practice remains uncertain due to limited evidence. A small study involving 70 babies showed that double nappies may enhance hip maturation, but more research is needed to determine their therapeutic role in treating hip dysplasia [12]. In another study, hip position was evaluated using ultrasound, comparing scenarios of no nappy, double nappy, and holding the baby in a "frog position" ("M" position"). Interestingly, the use of double nappies did not demonstrate any effect on hip position, while holding the baby in the "frog position" showed a positive influence [13].
Written by Dr Samuel Heitner
Resources:
Royal Children's Hospital Melbourne – Developmental dysplasia of the hip video - click here
International Hip Dysplasia Institute - click to view - Excellent resource.