Precocious appearance of the capital femoral ossific nucleus in larsen syndrome

Background: Larsen syndrome is associated with multiple complications, including spinal deformities and recalcitrant joint dislocations. We noted capital femoral ossific nuclei on ultrasonographic images that were made for two infants with Larsen syndrome who were less than two weeks of age. We sought to confirm that this finding is common in patients with Larsen syndrome and unusual in patients with normal hips or idiopathic developmental dysplasia of the hip. Methods: We identified eight patients with Larsen syndrome who had undergone ultrasonographic or radiographic evaluation of the hips before the age of three months. We compared the findings for these eight patients with those for forty consecutive patients from a prospective study of infants with developmental dysplasia of the hip who had ultrasonographic evaluation of the hips at approximately three months of age, including twenty patients who had normal clinical and ultrasonographic findings and twenty who had clinical instability of one or both hips. Results: All eight patients with Larsen syndrome had radiographic or ultrasonographic evidence of an ossific nucleus at an average age of forty days (range, six to 115 days); four of these patients had evidence of an ossific nucleus at six to ten days of age. In comparison, only two of twenty normal infants (three of forty hips) and one of twenty infants (two of forty hips) with developmental dysplasia of the hip had ultrasonographic evidence of an ossific nucleus at an average age of eighty-four days (range, seventy-six to ninety-four days) (p < 0.0001, Fisher exact test). Conclusions: In this small group of patients with clinically documented Larsen syndrome, the capital femoral ossific nucleus was evident on ultrasonography of the hip as early as six days of age and was unusual in normal patients or those with idiopathic developmental dysplasia of the hip. The detection of precocious development of a capital femoral ossific nucleus in infants being screened for skeletal anomalies may warrant further evaluation for the possibility of the presence of Larsen syndrome. Level of Evidence: Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.