A baby's pseudo paralysis of the hip stumps her doctors

Key Points

The Case

You are doing a pediatric nephrology rotation. It is late in the evening, and you're just about to leave for home when your pager goes off. You answer the call and learn about a 5-week-old girl who was seen in the orthopedic clinic that afternoon for developmental dysplasia of the hip (DDH).

The baby's pediatrician had noted asymmetric skin folds and limited abduction of the right leg during the Ortolani maneuver. Ultrasound of the hip confirmed a dislocated femoral head with a dysplastic right acetabulum. However, her physical exam was most remarkable for decreased movement of her leg. Her mother confirms that she has not seen the leg move "well" for at least 2 weeks. Because paralysis is not a typical presentation of DDH, a neurology consult was obtained.

Your neurology colleagues performed a detailed history and physical exam. The baby girl was born at 37 weeks by vaginal delivery without complications. There were no reported complications during pregnancy, and no medications, illicit drugs, or alcohol were used. She had limited prenatal care, with a single ultrasound at 12 weeks. Her mother, aged 28 years, received intrapartum penicillin for growth of group B streptococcus (GBS) on rectovaginal screening culture. The baby was discharged with her mother 72 hours after delivery.

At 2 weeks, the baby girl was admitted to a different hospital for respiratory syncytial virus bronchiolitis. She received supportive treatment and was discharged. However, her mother reports that a nurse commented that the infant did not move her right leg. The mother remembers this because the staff always used the right foot for monitoring because there was little motion artifact. Today in the clinic, the girl is intermittently irritable, especially if the right leg is moved. There is no history of trauma or fever. She is formula fed.

On physical exam, she is afebrile; pulse is 165; respiratory rate is 28 breaths per minute; blood pressure is 80/54 mm Hg; weight is 4 kg. She is alert and consolable. Her eyes fix on objects in front of her. Red reflexes are present. Pupils are equal and reactive. Her face is symmetric. Thumbs are flexed, but hands open easily.

She moves her upper extremities and left leg and foot well and equally. She has minimal movement of her right lower extremity with no abduction, adduction, flexion, or extension. She does have hamstring movements. She is able to dorsiflex and plantar flex her foot. She can flex her toes. Toe extension stops at neutral position. Pain and light touch sensation are intact throughout.

On the basis of the clinical history and physical exam, a differential diagnosis for lower extremity paralysis is developed (Table 1).^1-4 The leading diagnosis is right developmental hip dislocation with right lower leg paralysis because of femoral nerve involvement. Etiologies include congenital or traumatic nerve damage from the hip dislocation itself, birth trauma, or postnatal trauma. For further evaluation, she is admitted with plans for magnetic resonance imaging (MRI) of the pelvis and possible electromyogram (EMG) nerve conduction studies.