A patellar fracture is a traumatic break of the patella bone (knee cap).

patellar fracture

Sideview of the knee bones, showing a transverse fracture of the patella.

rupture of extensor mechanism

Showing a patellar fracture (middle image) compared to other ruptures of the extensor mechanism (ie the chain of structures that together straighten the knee).


How kneecap fractures occur

The kneecap may fracture from a direct impact, such as a fall on the knee. Or it may fracture from excessive extension force, such as in a weightlifter.


Consequences of a fractured patella

Because the patella may fracture in different ways there are different consequences. A small fragment may be pulled off, causing pain but not a huge amount of disability, while a complete transverse rupture may render incompetent the whole of the extensor mechanism of the knee, and the person may be unable to fully extend the knee or bear weight through it. The worse kind of fracture is a 'comminuted fracture, where the kneecap is shattered, and the parts may be forced apart, making any healing virtually impossible unless the surgeon is able to pull the pieces back into position and hold them there with wires for a sufficient time. The transverse fracture will also need wires to hold the parts together, as the extensor mechanism of the quads muscle will tend to pull the fragments apart.

Stiffness is a common consequence of patellar fracture.

Kneecap break
Fractured patella

Patellar Fracture Library

Library of excerpts from the medical literature about Patellar Fractures, with links to PubMed

Knee Fractures

A primer of the common fractures around the knee.

Patellar Fracture

Part of a primer on knee fractures

How urgent is your knee problem?

A list to help you in your own researches on your knee problem.



Imaging of patellar fractures. Jarraya M, Diaz LE, Arndt WF, Roemer FW and Guermazi A. Insights Imaging. 2017 Feb; 8(1): 49–57.

Current concepts review: Fractures of the patella. Gwinner C, Märdian S, Schwabe P, Schaser K-D, Krapohl BD and Jung TM. GMS Interdiscip Plast Reconstr Surg DGPW. 2016; 5: Doc01.

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