Delayed patellar ossification

What it means

Formation of bone in the patella later than normal.

The patella initially ossifies at between three and five years, commencing as multiple foci that rapidly coalesce. As the patellar ossification center enlarges the expanding margins may be irregular and associated with accessory ossification centers. These are most common superolaterally and may lead to the development of a bipartite patella. The bipartite patella has cartilaginous continuity despite the appearance of osseous discontinuity. The patella expands to all cartilaginous contours during late adolescence when the epiphyseal ossification centers around the knee are also in the final stages of maturation. The only cartilage not replaced is that occupying the superior two-thirds of the articular surface (the lower one-third is covered by the fat pad). The subchondral plate does not assume the actual articular contours until the late stages of osseous maturation (after ten to twelve years). Accordingly, typical measurements such as medial and lateral angulation cannot be accurately done prior to the final stages of patellar ossification expansion and maturation (PMID:6729496).

Rare diseases that can present with this2

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

Also called: Delayed bone maturation of the knee cap · Delayed patellae ossification