Differentials
Acetabular immaturity
SIGNS / SYMPTOMS
Typically differentiated by the alpha-angle on ultrasound. However, interobserver reliability of this measurement may be suboptimal.[19][20][21]
INVESTIGATIONS
Repeat ultrasound(s) over several weeks will typically differentiate from developmental dysplasia of the hip (DDH) before or by 3 months of age.
Proximal femoral focal deficiency
SIGNS / SYMPTOMS
Thigh is large and markedly shortened.
Sometimes associated with other skeletal anomalies such as fibular deficiency or knee hypoplasia.
INVESTIGATIONS
Radiographically distinct; femur is always distinctly abnormal in appearance.
Residual effects of septic arthritis
SIGNS / SYMPTOMS
Acute presentation with fever, irritability, poor feeding; pain on exam with internal rotation of flexed hip.
INVESTIGATIONS
Radiographically distinct.
X-ray may show osteonecrosis, varying degrees of femoral head disruption/destruction.
Fracture of femoral neck
SIGNS / SYMPTOMS
Uncommon in infancy.
INVESTIGATIONS
Radiographically distinct.
X-ray will show fracture.
Coxa vara
SIGNS / SYMPTOMS
Uncommon disorder.
Usually not appreciated until walking.
70% of cases are unilateral with leg-length discrepancy noted.
Physical exam: Trendelenburg gait.
INVESTIGATIONS
X-ray will show decreased femoral neck-shaft angle on anterior-posterior view (demonstrating a varus deformity), vertical epiphysis.
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