Developmental dysplasia of hip refers to patients being born with dislocation or instability of the hip, which may then result in hip dysplasia.
It means that there is an instability of the hip which results in changes in anatomical structures as the child grows. The structures that undergo dysplastic changes are the acetabulum and the proximal femur, as well as the labrum, capsule, and other soft tissue.
Earlier this condition was called congenital dislocation of the hip. Though this term is not all-encompassing, it is still called congenital dislocation of the hip among many clinicians across the world.
DDH involves abnormal growth of the hip.
Metatarsus adductus, torticollis have been found in some cases of developmental dysplasia of hip.
Oligohydramnios, a condition where liquor is reduced around the fetus has been associated with an increased prevalence.
Left hip is more commonly affected with this condition as compared to the right.
Few Definitions
Subluxation
Incomplete contact between the articular surfaces of the femoral head and acetabulum
Dislocation
Complete loss of contact between the articular surface of the femoral head and acetabulum. Most severe form.
Instability
Ability to subluxate or dislocate the hip with passive manipulation
Teratologic dislocation
Antenatal dislocation of the hip
Although the condition may be present at birth, it could also develop during the first year of life.
The condition can be bilateral or unilateral:
The overall frequency of developmental dysplasia of the hip is usually reported as approximately 1 case per 1000 individuals.
Relevant Anatomy
The growth of the acetabulum is dependent on the normal epiphyseal growth of the triradiate cartilage and presence of the spherical femoral head within the acetabulum.
The acetabulum appears as a condensation of mesoderm about the end of the fourth week of intrauterine life, but at first, it constitutes only a shallow socket on the outer aspect of developing innominate bone. Later, the socket is deepened by the progressive development of the original depression. The concavity of the acetabulum result from the pressure of the spherical femoral cartilaginous head.
Subluxation is an incomplete loss of contact and it does not always proceed to dislocation.
In the initial stages of the fibrocartilaginous limbus is subjected to pressure by the migrating head, a normal anatomical outline can be restored by concentric reduction of the head which will then provide the necessary stimulus to ossification.
In more advanced stages of subluxation, the head flattens the limbus and exerts a deforming pressure on the cartilaginous roof, causing further inhibition of ossification and actual flattening of the socket.
Dislocation occurs when the femoral head loses contact with the original acetabulum and rides up over the fibrocartilaginous rim.
Reduction of a dislocation is complicated by secondary changes that often includes the formation of a ridge called the neolimbus.
There could be barriers to a closed reduction in a dislocated hip. These are
- Adductor and psoas tendon contraction
- Ligamentous teres
- Transverse acetabular ligament
- Capsular constriction
- Interposition of the labrum in long standing cases.
Pathological Changes in Dislocated Hip
Image Credit
Changes in the bones
Acetabulum
- Shallower than normal
- Its rounded shape disappears, the cavity usually being converted into a triangular depression, with its base in front and below, and its apex above and behind.
- Instead of containing the head of femur, the acetabulum becomes occupied by
- Overgrowth of fibrocartilage
- Remains of the ligamentum teres
- Anterior portion of the capsule adherent to the floor.
- Above the acetabulum, there is a depression on the dorsum ilium, lined with periosteum, in which the head of the femur rests insecurely. A fold of the capsule intervenes between the ilium and the head.
Femur
- The femoral head is at first normal, although ossification of it is often delayed and there is a marked discrepancy between the size of the cartilage head and the reduced acetabulum.
- Later it becomes flattened on its medial and posterior aspects.
- Marked shortening of the neck of the femur
- Increased anteversion of neck
Pelvis
Ipsilateral pelvic bone is imperfectly developed, and the whole pelvis has a lateral inclination, while the shape of the inlet is obliquely ovoid.
When there is a bilateral dislocation, the pelvis is tilted forwards and the normal lumbosacral lordosis increased. The whole innominate bone may be small an atrophied, and lies more vertically than than normal
Soft Tissue Changes
Capsule
Capsule can assume an hourglass shape, one cavity containing the head, other covering the acetabulum, and the constriction between them being produced by the iliopsoas tendon which crosses the capsule at this level.
Through this narrow isthmus, the ligamentum teres passes. The lower part of the capsule is stretched across the entrance to the contents. It will thus be seen that the capsule becomes a suspensory ligament for the pelvis, and, indeed, supports most of the weight of the body.
It therefore undergoes hypertrophy, particularly at its anterior and lower portion. The ligamentum teres is usually attenuated. In certain cases, hypertrophy of the ligamentum teres occurs.
The muscles
The pelvifemoral group, adductors, hamstrings, graciliss, sartoris, tensor fasciae latae, pectineus and rectus femoris shorten, and make reduction difficult.
The pelvitrochanteric group, obturators, quadrates femoris and psoas tendon become functionally stretched and elongated and therefore incompetent. They also serve to block the reduction.
The gulteal group show little organic change but power is considerably diminished as displacement of the head leads to an alteration in their axis of movement.
With unilateral complete dislocation, secondary problems can arise in the back such as a scoliosis, leg length problems with gait disturbances, due to the fixed adduction position of the involved hip and valgus deformity of the ipsilateral knee, followed by degenerative arthritis.
Causes of Delopmental Dysplasia of Hip
The cause of hip dysplasia is not clear and the condition is considered to be multifactorial
- Genetic – Prevalence much higher in Native Americans and Laplanders and very low in Chinese and black populations. Moreover, hip dysplasia is 10 times higher in children whose parents had it.
- Female sex
- First-born child
- Breech intrauterine positioning
- Acquired causes –
- Infant swaddling
- Overly restrictive baby seats, carriers
- Use of a cradle board which keeps the hip joint in an adducted position
Crowe Classification of Developmental Dysplasia of Hip
Crowe I
Femur and acetabulum show minimal abnormal development.
Less than 50% dislocation
Crowe II
The acetabulum shows abnormal development.
50% to 75% dislocation
Crowe III
The acetabula is developed without a roof. A false acetabulum develops opposite the dislocated femur head position.
75% to 100% dislocation
Crowe IV
The acetabulum is insufficiently developed. Since the femur is positioned high up on the pelvis this class is also known as “high hip dislocation”.
Clinical Presentation
Newborns are examined in routine for detection of developmental dysplasia of the hip.
This is done by clinical examination of a newborn by Ortolani maneuver. Ultrasound has been suggested s screening apparatus but subjecting every child to ultrasonographic examination is not cost effective and could lead to overdiagnosis too.
Ortolani Maneuver
For this maneuver, the patient must be relaxed. Only one hip is examined at a time. The examiner’s thumb is placed over the patient’s inner thigh, and the index finger is gently placed over the greater trochanter. The hip is abducted, and gentle pressure is placed over the greater trochanter.
A clunk is heard when dislocated hip moves into the acetabular socket if developmental dysplasia of the hip is present.
This maneuver would miss subluxatable or dislocatable hips. Barlow’s maneuver is reverse of this maneuver and tries to dislocate the hip.
Barlow’s Test
Barlow test is performed with the hips in an adducted position, in which slight gentle posterior pressure is applied to the hips. A “clunk” should be felt as the hip subluxates out of the acetabulum.
If a child present late [3-6 month], the dislocation becomes fixed.
Following video explains both the maneuvers
Galeazzi sign is a useful sign to identify unilateral hip dislocation in these children. This is performed with the patient lying supine and the hips and knees flexed. The knees appear at different levels with the affected knee at a lower level.
The finding is due to apparent shortening of the affected limb [Due to dislocation, there is proximal migration and thus apparent shortening]
It is important to realize that any limb-length discrepancy results in a positive Galeazzi sign.
Other findings in these children are
- Asymmetry of the gluteal and thigh skin folds
- Decreased abduction[adduction contracture] on the affected side
- Leg-length inequality
- High riding trochanter
- Lesser resistance to examining finger when femoral head is palpated
- Buttock may be underdeveloped.
When a child is seen after she has started walking, the gait is found to be abnormal. The child walks with a lurch towards the affected side due to the inefficiency of the gluteal muscles, the shortening of the neck of the femur, and the displacement of the head, combined with the lordosis and the abnormal lateral mobility of the lumbar spine.
There would be inequality of leg length and Trendelenburg’s sign is present [This sign denotes deficiency of hip abductors like gluteus medius and not specific for hip dislocation.]
Bilateral dislocation of the hip is more difficult to diagnose and often manifests as a waddling gait with hyperlordosis. Galeazzi sign, asymmetric thigh and skin folds, or asymmetrically decreased abduction are absemt.
Imaging
Ultrasonography
Ultrasonography is an excellent tool for assessing children with suspected hip instability and a useful aid in the treatment monitoring.
X-rays
Anteroposterior view of the pelvis, with the hips in a neutral position.
For the acetabular profile, xrays angled at 65º are taken.
An abducted internal rotation view can help determine neck shaft angle and whether the hip reduces.
On x-ray, the evaluation is done with help of various lines drawn on xray.
These are
Hilgenreiner line
Hilgenreiner line is through the superior aspect of both triradiate cartilages. It should be horizontal but is mainly used as a reference for Perkin line and measurement of the acetabular angle.
Perkin line
Perkin line is perpendicular to Hilgenreiner line and intersects at the lateral most aspect of the acetabular roof. It along with Hilgenreiner line divide each hip in four quadrants.
Upper femoral epiphysis [usually observed in patients aged 4-7 months] should be seen in the inferomedial quadrant (i.e. below Hilgenreiner line, and medial to Perkin line)
Acetabular angle
The acetabular angle is formed by the intersection between a line drawn tangential to the acetabular roof and Hilgenreiner line.
This angle is approximately 30 degrees at birth . It decreases with age and should measure less than 20° by 2 years of age.
Shenton line
Shenton line or arc is drawn along the inferior border of the superior pubic ramus and continue laterally along the inferomedial aspect of the proximal femur as a smooth line.
In cases where there is a superolateral migration of the proximal femur due to developmental dysplasia of hip then this line will be discontinuous, also termed as broken Shenton arc.
Disruption of the Shenton line indicates the presence of some degree of hip subluxation.
Following x-ray is of congenital dislocation in an adolescent. Note the shallow acetabulum and proximal migration along with false acetabulum.
CT
Computed tomography can also be helpful in determining femoral anteversion and in determining the extent of posterior acetabular coverage. Three-dimensional images are also quite popular and can be beneficial in visualizing the overall shape of the acetabulum.
MRI
Magnetic resonance imaging can be beneficial in identifying the underlying bony and soft-tissue anatomy.
Arthrography
Arthrography is performed by injecting radiopaque dye into the hip joint and then carrying out a fluoroscopic examination, usually with the patient under anesthesia.
Arthrography is helpful in determining the cartilaginous profile and dynamic stability of the hip.
It can also help to assess the adequacy of the reduction.
Differential Diagnoses
- Coxa vara
- Pathological dislocation.
- Paralytic dislocation of poliomyelitis.
- Cerebral palsy.
- Proximal femoral Deficiency
Treatment of Developmental Dysplasia of Hip
The natural history of developmental dysplasia of hip depends on the severity of disease, whether unilateral or bilateral condition and whether false acetabulum is formed or not.
The development of a false acetabulum is associated with a poor outcome in approximately 75% of patients.
Bilateral hip dislocation in a patient without false acetabula has a better overall prognosis.
Unilateral dislocations result in significant leg-length inequality, with a gait disturbance and possibly associated hip and knee pain.
<6 months
Earlier the condition is recognized, better is the prognosis. These children are treated with pavlik harness or some similar brace that keeps the hips in abducted position.
Ultrasonography can be used to assess the reduction and monitor the reduction in follow up.
If the hip is posteriorly subluxated on ultrasound in spite of use of Pavlik Harness therapy should be discontinued.
In case the reduction is successful, the harness should be continued until the hip is considered to be stable both on clinical grounds and ultrasonographic findings with the patient out of the brace.
In case of presence of residual dysplasia, abduction splinting is maintained.
Failure with Pavlik harness warrants closed reduction.
>6 months
In patients older than 6 months, the success rate with a Pavlik harness is less than 50%. Therefore, Pavlik Hharness should not be used in these patients.
If the child is diagnosed when older than 6 months or if the Pavlik harness is determined to be unsuccessful, a closed reduction is attempted.
Arthrography can be used to check the adequacy of closed reduction. Following reduction, the hip is immobilized in hip spica cast for 6-12 weeks. Hip is reexamined after this period and if stable ble, the patient is placed in an abduction brace. If the hip remains unstable, the patient is again placed in a spica cast.> 2 years or open reduction
> 2 years
These hips are not amenable to closed reduction and require surgery in form of open reduction with or without additional procedures.
It should be noted that late diagnosis or greater age necessitates the surgery but surgery should be done in patients of developmental dysplasia of hip only when the results of such treatment would be better than the results of the natural progression of the disease.
Open reduction is the treatment of choice for developmental dysplasia of hip in children who are older than 2 years at the time of the initial diagnosis or in whom attempts at closed reduction have failed. Preoperative traction is helpful.
In a child older than 3 years, femoral shortening osteotomy may be needed and is a better choice than preoperative traction. At that time, if proximal femoral dysplasia is present, such as that observed with significant anteversion or coxa valga, this can also be corrected.
Some surgeons advocate shortening femoral osteotomy in children between 2-3 years too.
Pelvic osteotomy may be needed for residual hip dysplasia. A period of 18-24 months should pass if closed reduction has been done. This is done to allow for acetabular remodeling.
If open reduction is performed in a child older than 4 years with significant hip dysplasia, an acetabular procedure should be considered at the time of open reduction.
Various acetabular procedures are Salter, Pemberton, Chiari and Schanz osteotomy
After open reduction, hip spica cast is advised for 6-12 weeks, followed by abduction orthosis.
Contraindications to Surgery
- Age >8 years for a unilateral hip dislocation or >4-6 years for bilateral hip dislocation
- Neuromuscular disorder
- Spinal cord injury
- Cerebral palsy in a patient who has had a hip dislocation for longer than 1 year.
Arthrodesis and arthroplasty are procedures of choice for young adults with hip osteoarthritis.
Prognosis of Developmental Dysplasia of Hip
Left alone, the developmental dysplasia of hip is not a major disability in early ages. Symptoms increase during the adolescent period and later, arthritis leads to painful hip.
If diagnosed early and treated successfully, children are able to develop a normal hip joint and should have no limitation in function.
Even with appropriate treatment, hip deformity and osteoarthritis may develop later in life. This is especially true when treatment begins after the age of 2 years.
Overall, the prognosis for children treated for hip dysplasia is very good, especially if the dysplasia is managed with closed treatment.
With the open reduction, outcomes are less satisfactory than may be less. When secondary procedures are needed to obtain a reduction, the outcome is not as good.
Bilateral hip dysplasia has frequent delays in diagnosis and require greater treatment and is thought to have a worse prognosis.
Complications associated with developmental dislocation of the hip are redislocation, the stiffness of the hip, infection, blood loss, and, avascular necrosis of the femoral head.
