Presentation
Painful left knee after direct trauma.
Patient Data
Evidence of full-thickness chondral disruption (chondral delamination) of retropatellar cartilage of the medial articular facet at the upper patellar pole at the insertion of medial patellar retinaculum with elevated (6 mm) chondral fragment, (4 mm) intra-articular chondral loose body, and marrow edema of the upper patellar pole.
Edema and swelling of the medial patellar retinaculum, reflecting ligamentous strain.
Moderate knee effusion is noted.
Mild subcutaneous edema and prepatellar bursitis noted.
Hoffa fat pad and anterior suprapatellar fat pad edema.
Wiberg type III patellar shape and shallow trochlear groove.
Case Discussion
This is an unusual post-traumatic sequel with full-thickness articular cartilage avulsion of the medial articular facet at the upper pole and loose chondral fragment. This is one of the forms of high grade patellar articular cartilage injuries. This is considered a grade 5 patellar cartilage injury 1.
The location of the avulsed fragment at the insertion of medial patellar retinaculum and Wiberg type III shape of patella raise the possibility of transient lateral patellar dislocation during injury. There is also a decreased trochlear depth indicating trochlear dysplasia, which is a risk factor for patellofemoral instability.
Osteochondral fractures of the patella are commonly associated with acute patellar dislocations. In most cases, the osteochondral fracture is located in the medial facet of the patella.
This injury is similar in appearance to patellar sleeve avulsion fracture that occurs in children (immature skeleton), where a cartilage cap of the patella is avulsed due to quadriceps forceful action.
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