A 5-day-old infant was referred to the pediatric orthopedic clinic for evaluation of a left hip “clunk.” She is a firstborn child, born at full term (39 weeks) via cesarean delivery secondary to breech presentation. Her weight at birth was 7 lb 6 oz. The infant was noted to have a left hip clunk during a routine physical examination by her pediatrician, who made a referral to the pediatric orthopedic clinic for possible hip dysplasia. This is the patient’s first visit to the clinic.
There is no family history of hip dysplasia or other orthopedic abnormalities. The infant is a well-appearing, alert female measuring 20.5” in length and weighing 7 lb 4 oz. Vital signs are stable with no abnormality detected. The heart is regular in rate and rhythm, and the chest is clear bilaterally.
No cutaneous abnormalities are noted. The patient is able to move all her extremities spontaneously, and her spine is straight and normal with no evidence of spinal dysraphism. Her feet are normal bilaterally, with full range of motion and no equinovarus or metatarsus adductus deformity.
The neurologic examination is also unremarkable, with normal neonatal reflexes and excellent muscle tone throughout.
Examination of the infant’s hips reveals a positive result on the Barlow test on the left side (the hip can be dislocated). There is also a positive Ortolani sign (the hip can be reduced), with asymmetric thigh skin folds noted (see Figures 1A and 1B, respectively).
Based on these positive physical examination findings, the patient was diagnosed with developmental dysplasia of the hip (DDH). Initial ultrasonography to confirm the diagnosis was not considered necessary, as the physical examination demonstrated obvious instability.1 The infant was placed in a Pavlik harness, which her parents were instructed should be worn full-time (see Figures 2A and 2B). She was scheduled for weekly follow-up visits for adjustments to the harness and serial hip examinations.
At the second follow-up visit, ultrasonography was performed, confirming the presence of dysplasia with decreased femoral head coverage and a steep socket (acetabulum). Use of the Pavlik harness was continued full-time for six weeks.
At age 6 weeks, the infant underwent a follow-up ultrasound to assess for improvement in the degree of dysplasia. The test revealed normal hips bilaterally with no evidence of DDH. Therefore, use of the Pavlik harness was discontinued. The parents were instructed to bring the child back in six months for a repeat clinical examination and an anteroposterior x-ray of the pelvis.1
Discussion
The term developmental dysplasia of the hip (DDH) has replaced the more traditional term congenital hip dislocation because DDH more accurately reflects the variable characteristics that can be seen with this condition. As DDH may not be present at birth, the term congenital is misleading. We now know that DDH may occur in utero, perinatally, or during infancy and childhood.2,3
Generally, DDH is used to describe an abnormal relationship between the femoral head and the acetabulum (see Figure 34). The term represents a wide spectrum of abnormality, as shown in the Graf classification of hips in infants: type I refers to a normal hip; type II, immature development to mild dysplasia; type III, subluxation of the femoral head; and type 4, frank dislocation with severe instability.5
Diagnosing and managing DDH correctly requires the clinician to have a thorough understanding of the normal growth and development that occurs in the hip joint. Embryologically, the joint (including the femoral head and acetabulum) develops from the same primitive mesenchymal cells.6 By 11 to 12 weeks’ gestation, the initial structures of the hip joint are fully formed; theoretically, this is the earliest time at which a dislocation can occur.2,7 DDH that develops at this stage would be called teratologic; this condition is seen most frequently in patients who have underlying neuromuscular conditions, such as myelodysplasia (spina bifida) or arthrogryposis. A typical dislocation takes place during the perinatal period in an infant who is otherwise healthy.2
Etiology
DDH occurs in about 11 of every 1,000 infants, with frank dislocations occurring in one to two infants per 10,000.8 The left hip is involved in approximately 60% of cases, the right in 20%, and both hips in about 20%. In the most common intrauterine fetal position, the left hip is lower than the right (usually abutting the mother’s sacrum) and is often in adduction. This is likely the reason that the left hip is more commonly affected by DDH.
DDH is believed to be multifactorial, with physiologic, genetic, and mechanical factors implicated in the etiology.3 The incidence of DDH varies with factors such as the patient’s age, race, and gender, the experience and training of the examiner, and the diagnostic criteria that are used.