HSS Ultrasound of the Month Case 84

Clinical History 7 month old boy with congenital flexion contracture of the left knee Clinical concern was for congenital patellar dislocation

Ultrasound of the Month – Case 84

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Diagnosis: Congenital patellar dislocation Discussion Congenital patellar dislocation is a rare condition in which the infant or toddler may present with a flexion contracture of the knee, genu valgum, or delayed walking.

Although it may occur in isolation, there is an increased incidence of syndromic associations, including Larson syndrome, nail-patella syndrome, Down syndrome, and Ellis-van Creveld syndrome.

Because the patella does not begin to ossify until 3-4 years of age, congenital patellar dislocation cannot be confidently diagnosed on radiographs.

MRI and CT scan can diagnose this entity, although the former is expensive and may require sedation, while the latter involves ionizing radiation.

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Discussion - continued Ultrasound can identify both ossified bones as well as bones that are not yet ossified, making it a quick and accurate exam for evaluating many osseous structures in infants.

Identifying the position of the unossified patella with respect to the femoral trochlea can easily diagnose or exclude patellar dislocation.

Dynamic maneuvers performed concurrently can assess whether the patellar dislocation, if present, is fixed or reducible.

Treatment of congenital patellar dislocation is surgical, as there is a high risk of permanent deformity and early osteoarthritis if left untreated.

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