Developmental Pediatric Hip Dysplasia - An Overview

Overview

Developmental pediatric dysplasia of the hip is the term used to describe a broad spectrum of abnormalities of the hip joint that may be present around the time of birth or may present during childhood.

In the healthy hip joint, the upper end of the thigh bone or femur meets a curved portion of the pelvis called the acetabulum to fit together like a ball and cup, in which the ball rotates freely in the cup. Cartilage, a smooth protective tissue, lines the bones and limits friction between the surfaces during movement.

Line drawing of femur and acetabulum in healthy hip joint

In developmental hip dysplasia, however, one or more of these functions work incorrectly. The conditions encompassed by this term include:

• Dislocated Hip: there is no contact between the cartilage on the ball and the cartilage on the cup
  
• Dislocatable Hip: the ball and cup easily pop in and out
  
• Subluxatable Hip: the cartilage of the ball or femoral head and the cup are touching, but the ball is not properly seated in the cup
  
• Dysplastic Hip: ball, cup or both are malformed

Preop x-ray of dislocated right hip.

Causes

Genetics plays a strong role in the incidence of hip dysplasia. If a parent has a history of hip dysplasia in childhood, the risk of hip dysplasia in a child is increased to 12%. If another child in the family has hip dysplasia, the risk of hip dysplasia is increased to 6%. Overall, the risk of hip dislocation at birth is approximately one in one thousand. Even without a hereditary link, there is a greater risk in all first-borns. Breech birth-in which the baby emerges from the birth canal buttocks first-increases the risk of hip dysplasia by ten-fold.

After birth, the presence of other molding abnormalities associated with a constrained intrauterine environment (a condition in which the uterus forms a "tighter package" around the fetus) may also alert the pediatrician to the possible presence of hip dysplasia. These include torticollis or head tilt, and metatarsus adductus or turning in of the front portion of the foot.

Hip dysplasia is much more common in girls than in boys and more frequently affects the left hip than the right; about 80% of cases follow this pattern. The condition may also be present in both hips.

Diagnosis

When developmental hip dysplasia is present at birth, the abnormality may be detected during a routine physical examination of the newborn. During this examination, the physician gently flexes the child's hips in different directions. If the hip is dislocated, dislocatable, or subluxatable, he or she may feel a "clunk" as the hip moves out of alignment.

In a smaller percentage of cases, the problem does not become apparent until later in infancy or early childhood. Later diagnosis of hip dysplasia may be detected during routine examinations of hip stability in the pediatrician's office. Signs that may bring undiagnosed developmental hip dysplasia to the attention of parent and physician include a leg length discrepancy on the affected side, a limp, and, if both legs are affected, a waddling gait. These children may also have a restricted range of motion.

To confirm a diagnosis of developmental hip dysplasia in children up to 4-6 months of age, the orthopaedist uses an ultrasound. This technology offers a significant advantage over conventional x-rays in that the images may be taken with motion. "This is a very accurate and safe diagnostic tool since there is no radiation," according to Roger F. Widmann, Assistant Director of the Pediatric Orthopaedic Service and Co-Chief of Limb-Lengthening Service at the Hospital for Special Surgery (HSS). In children older than 6 months, traditional x-rays, which show better bone detail, are used to confirm the diagnosis.

Treatment Options

In order to ensure proper development of the bones that make up the hip joint, early intervention is essential. "The acetabulum and the femoral head are dependent on one another for normal growth and development," explains Dr. Widmann. "If the ball does not fit tightly into the cup, providing a specific growth stimulus, the cup may become too flat and unable to accommodate a sphere. In turn, without proper contact with the acetabulum, the femoral head and neck will not grow normally."

Pavlik Harness

For patients up to six months of age, the first choice of treatment for hip dysplasia, is the use of the Pavlik harness, a soft brace that gently redirects the head of the femur into the depth of the socket or acetabulum, stimulating normal development of the joint. The harness is generally used for three months total, initially full-time and as the hip position improves and stability is achieved, part-time harness treatment may be instituted. Treatment with the Pavlik harness is successful in about 85% of dislocated hips in children under six months of age.

Pavlik Harness is a soft brace used for patients up to 6 months old.

Reduction

For the small number of patients in whom treatment with the harness is not successful, and for children in whom the diagnosis is not made until after they are six months old, the orthopaedist may recommend either closed or open reduction, a procedure in which the bones are realigned, or put back into place. Unfortunately, the Pavlik harness is not a good treatment option for older children because the hip has become more fixed in the dislocated position, and is less easily realigned.

Reduction procedures are performed by pediatric orthopaedists with specialized experience in the treatment of hip dysplasia. During a closed reduction procedure, the physician gently manipulates the hip into proper alignment under radiographic control without making an incision.

Arthrogram image of dislocated hip in the operating room.

Following closed reduction of the hip, the patient is placed into a spica body cast for 12 weeks to maintain proper alignment of the hip and acetabulum. It is mandatory that cross-sectional imaging of the hip be performed after closed reduction in order to confirm appropriate location of the hip. Current imaging modality of choice at HSS is MRI, since MRI does not involve radiation.

Image of relocated hip on MRI.

Following closed reduction, patient wears spica body cast.

Treatment by open reduction is generally reserved for children 18 months of age to two years with a new diagnosis of a dysplastic hip, or in cases in which closed reduction of the hip has not been successful. In this procedure, the surgeon makes an incision, removes any obstacles to proper re-alignment of the hip (adjusting tight muscles or other soft tissue) and re-locates the femoral head into the acetabulum. He or she may also need to restore normal anatomy by performing an osteotomy, a procedure in which cuts are made to the femur or the acetabulum. The need for osteotomy increases with the age at which diagnosis is made, and is usually required in the child over age 3 or 4 to correct abnormal development of the bones.

Pre-op right hip dislocation - right leg appears short.

All reduction procedures, including those that include osteotomy, are done on an in-patient basis and require the use of a general anesthetic.

Children who undergo open reduction wear a cast for a period of 6-8 weeks. Once the cast is removed, he or she usually continues to wear a brace at night until such time that the orthopaedist has determined that normal hip development is proceeding.

X-ray 6 months after open reduction with located right hip.

Pelvic osteotomy and reorientation of the acetabulum is occasionally necessary in the setting of residual hip dysplasia after open or closed reduction of the hip. In younger patients the procedure of choice is often the Dega osteotomy in which the bony and cartilage roof of the hip is reoriented into normal alignment.

X-ray showing residual acetabular dysplasia on right side.

Immediate post-op image of pelvis and hip after Dega pelvic osteotomy.

Final appearance of pelvis and hip 18 months after Dega pelvic osteotomy.

Risks

Regarding the safety of these procedures, Dr. Widmann says, "What I usually tell parents is that the primary risk with a diagnosis of developmental hip dysplasia is not doing anything at all. Untreated, these children face a high risk of developing osteoarthritis as adults with the associated degenerative changes that cause chronic and progressive pain and stiffness." Although the numbers are difficult to define, some members of the medical community believe that up to 50% of adults who eventually require hip replacement due to osteoarthritis, have developed the disease as a result of an undiagnosed pediatric hip problem. The majority of those cases are thought to be residual undiagnosed hip dysplasia.

The risks associated with surgery-bleeding, infection, and those associated with anesthesia-are minimal, according to Dr. Widmann. Pediatric orthopedists do take special care to avoid a condition called avascular necrosis (AVN) in which the femoral head-the ball of the hip-does not receive enough blood, a condition that can result in abnormal growth of the bone.

Outcomes

As noted, the earlier the condition is treated, the better the chance of successful outcome, which is gauged as a hip that appears anatomically normal both during physical examination and on x-ray. Children who are treated for hip dysplasia are examined on regular intervals until they are skeletally mature (when growth is completed), to ensure that normal development continues. In some cases, a dislocated hip that was successfully reduced may still develop dysplasia in later years that requires additional treatment.