Patellar avulsion fracture, articular loose body, old Stieda-Pellegrini lesion

Case contributed by Dr Balint Botz

Presentation

Kicked in the left knee while playing football, unable to bear weight.

Patient Data

Age: 20
Gender: Male

On the first look the most striking abnormality is a calcification adjacent to the medial femoral condyle, corresponding to the location of the MCL. This is however a chronic condition, corresponding to a Stieda-Pellegrini lesion due to prior avulsion injury of the MCL.

The suprapatellar recess is widened, and of reduced transparency, suggestive of articular effusion - considering the acute setting most likely due to hemarthrosis.

A more closer scrutiny reveals a tiny avulsed bone flake next to the the distal aspect of the patella (see magnified key image), corresponding to an avulsion fracture of the patella

For further evaluation for operative management a noncontrast CT was requested. 

CT confirmed the patellar avulsion fracture, as well as the resultant articular effusion, which most likely is blood mixed with synovial fluid due to its density (20-30 HU). A small calcified flake - an articular loose body - was detected in the suprapatellar recess.

Case Discussion

The case demonstrates patellar avulsion fracture with consequent hemarthrosis, which presented overlapping with a chronic Stieda-Pellegrini lesion, and an articular loose body, which is likely the result of prior injuries. 

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Case information

rID: 62460
Published: 18th Aug 2018
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included
Institution: University of Pécs

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