Imaging Case of the Week 551 Answer

The knee x-ray shows a bipartite patella.

The superolateral aspect of patella shows a well corticated fragment, which can be easily mistaken for a fracture. The typical appearance indicates that this is a bipartite patella. The lateral knee x-rays show no evidence of effusion or a lipohaemarthrosis which also goes against a fracture.

As always, clinical examination is the key and if available, look at old images which should have similar appearance.

Be familiar with this anatomical variant, found in about 2% of population, bilateral in 30-40%,

Further reading