Background: Progressive pseudorheumatoid dysplasia (PPRD), a noninflammatory condition, needs to be differentiated diagnostically from juvenile rheumatoid arthritis (JRA).
Objective: Demonstration of an unusually large and often early-appearing os trigonum helps distinguish PPRD from JRA.
Materials and methods: Ankle images in four children with PPRD were reviewed.
Results: The os trigonum was abnormally enlarged in all PPRD subjects and was shown to have appeared or fused earlier than normal in two subjects.
Conclusion: A large and early os trigonum ossification helps differentiate PPRD from JRA.