Don’t be too focused on the abdo in an abdo x-ray….

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This is a 5-month old female who presented to a rural emergency department because of lethargy, fussiness, vomiting, and blood in the stool. An abdominal mass was noted on exam and intussusception was suspected. Abdominal films and a barium enema were done.

The barium enema demonstrated intussusception which was successfully reduced with the barium enema. This child was then transported to a children’s hospital for hospitalization under the care of a pediatric surgeon.

Overnight she was kept NPO with IV fluids infusing. After improving overnight, she was started on oral fluids in the morning. However, she vomited twice that afternoon. Her abdominal exam was benign but because of her previous intussusception, an abdominal series was ordered.

Upright view

Supine view

These radiographs showed some dilated loops and a paucity of bowel gas. There is a small amount of barium remaining (following the barium enema done at the rural hospital). The liver edge is not well defined. This is sometimes seen in intussusception but it is not specific.

The more specific plain film signs of intussusception (the crescent sign and the target sign) are not present.

Her abdominal radiographs were felt to be non-specific at this point. She continued to feed and her symptoms resolved by morning at which time she was discharged.

So, what’s the twist?

Her abdominal series discovered a congenital dislocated left hip (identified by the radiologist) which was previously undiagnosed on routine newborn screening exams. She was referred to an orthopedic surgeon for this condition. Congenital hip dislocation is part of the spectrum of congenital dysplasia of the hip. Hip dysplasia can range from a barely detectable instability of the hip to a non-reducible dislocation of the hip. Very mild cases may resolve on their own without any long term morbidity. More severe cases result in the progression of symptoms and if not diagnosed at an early stage can lead to an irreversibly damaged hip.

Early diagnosis and treatment of congenital hip dysplasia is required to prevent permanent injury to the hip. Physicians providing primary care for infants routinely screen for hip dysplasia through routine screening examination methods. However, there is no clinical finding or screening method that can reliably detect all cases. For this reason, patients with an undiagnosed occult hip dysplasia, may seek treatment in an ED for an abdominal condition.

If an abdominal radiograph is ordered on such a patient, the diagnosis may be apparent radiographically if one is astute enough to survey the bony structures. Failing to identify a congenital hip dislocation on a radiograph may result in liability if the patient’s condition is ultimately diagnosed after irreversible hip damage is sustained. Protection from liability is not afforded even if the radiograph was ordered for a different reason.

Radiographs are usually kept indefinitely. Thus, at any time in the future, our interpretation of a radiograph may be subjected to a retrospective review. In older children with a well ossified hip, it is usually obvious if the hip is dislocated since the well developed femur head is easily seen to fit symmetrically within the acetabulum bilaterally. In younger children where the acetabulum is not fully ossified and the femur head is non-ossified or is just beginning to ossify, the relationship between the femoral head and the acetabulum is not easy to assess radiographically. In infants, ultrasound of the hip may be the diagnostic method of choice in defining the anatomy of a suspected dysplastic hip.

Here’s the hip anatomy part….

A horizontal line is drawn as shown (through the triradiate cartilages). Vertical lines are drawn as shown (through the lateral edge of the acetabulum). The black arc drawn over the patient’s left hip (right side of the image) outlines the upper border of the acetabulum. The vertical lines are drawn through the lateral edge of this border. These perpendicular lines form four quadrants about each hip. The ossified femoral head should be normally located in the inferior medial quadrant.

In this case, the femoral heads are not ossified so it is not visible on the radiograph. It is not hard to imagine the position of the femoral head (epiphysis) located proximal to the femur along its long axis. The patient’s left femoral head (right side of the image) would be in the superior lateral quadrant (indicating dislocation), while the patient’s right femoral head (left side of the image) would be in the inferior medial quadrant (normal position).

If the femoral head is not ossified, the medial “beak” of the proximal femoral metaphysis should be in the medial inferior quadrant. In this case the white arrows point to the “beaks” on both sides. The patient’s left femoral beak is in the inferior lateral quadrant (indicating dislocation), while the patient’s right femoral beak is located in the medial inferior quadrant (normal position).

Shenton’s line is a smooth arc drawn from the medial femoral neck through the superior margin of the obturator foramen. If this arc cannot be drawn smoothly, dislocation is suspected. Note the smooth arc of Shenton’s line drawn on the patient’s normal right hip (white arc) while this arc cannot be drawn over the patient’s dislocated left hip. In the abnormal left hip, the arc is discontinuous.

How do we pick this up clinically?

Children may occasionally present to the ED for evaluation of a limp if they have no primary care provider or if the patient’s primary care provider fails to properly evaluate the child to the parent’s satisfaction. When the child begins walking, the most common diagnostic sign is an abnormal gait. This can be so subtle that it may be difficult to appreciate. It is often best to rely on the parents’ assessment of the child’s gait since they are usually more sensitive at observing such subtle abnormalities.

Other signs may be subtle and difficult to appreciate. There may be asymmetry in lower extremity length measurements. Because asymmetry may not be present in bilateral hip dysplasia, this may be more difficult to detect than unilateral disease. Radiographs should be more reliable in identifying abnormalities in the well ossified hip. Ultrasound is more accurate in defining the hip anatomy in infants. Most infants with congenital hip dysplasia can be detected by screening exam measures. This responsibility rests largely with primary care physicians. However, not all children have access to a primary care physician.

Infant growth and development changes the musculoskeletal structure of the hip such that screening exam measures become less reliable in detecting hip dysplasia as the infant grows. The Ortolani and Barlow signs have usually disappeared by six weeks of age. Detection of congenital hip dysplasia outside of this age relies on the identification of subtle findings such as lower extremity length asymmetry, loss of the normal hip flexion contracture, buttock fullness, a hollow anterior groin, asymmetry of the perineal, gluteal or thigh folds/creases, or a palpably dislocated femoral head. The Ortolani sign (reduction of the dislocated hip by abduction) and the Barlow sign (dislocation of a reduced hip by adducting and applying longitudinal pressure on the femur) used in newborn screening refer to the sequential series of maneuvers testing the reducibility and dislocatability, respectively, of the hips. If the nomenclature is confusing, it may be more useful to describe a hip as being dislocatable/reducible and/or as stable/unstable.

References

The Hip. In: Renshaw TS. Pediatric Orthopedics. Volume 28 in the Series, Major Problems in Clinical Pediatrics. Philadelphia, W.B. Saunders, 1986, pp. 63-89.

Herring JA. Congenital Dislocation of the Hip. In: Morrissy RT (ed). Lovell and Winter’s Pediatric Orthopedics, 3rd edition. Philadelphia, J.B. Lippincott Co., 1990, pp. 815-851.

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Prof Loren Yamamoto MD MPH MBA. Professor of pediatrics at the University of Hawaii and a practising pediatric emergency doctor in Honolulu. | Contact | View Loren's DFTB posts