Double-layered patella

What it means

An anomaly of the patella characterized by two layers visible on lateral knee X-ray such that one layer is in front of the other in the sagittal orientation (See Figure 2A and 3B of PMID:12966518). This finding persists into adulthood.

This feature can be observed in Multiple epiphyseal dysplasia type 4. It is distinct from bipartite patella, which is characterized by an unfused accessory ossification center at the superolateral aspect of the patella. Double layer patella appears to be caused by the presence of several patellar ossification centers.

Rare diseases that can present with this1

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category