Patellar dislocation with chondral injury

Case contributed by Dr Joachim Feger

Presentation

Pain and swelling of the knee, after a lateral patellar dislocation.

Patient Data

Age: 20 years
Gender: Female

Findings:

  • a small avulsed fragment at the medial rim of the patella

Impression:

  • medial avulsion fracture of the patella

Findings:

  • large knee joint effusion

Intercondylar region:

  • unremarkable anterior and posterior cruciate ligaments
  • two loose chondral fragments between the anterior transverse meniscal ligament and the intercondylar groove

Medial compartment:

  • unremarkable cartilage and medial meniscus
  • soft tissue edema
  • thickening of the superficial part of the medial collateral ligament small tear within the proximal part

Lateral compartment:

  • bone contusion of the anterolateral rim of the lateral femoral condyle
  • extensive chondral lesion of the antero- and centrolateral femoral cartilaginous zone with delamination
  • normal lateral collateral ligament and posterolateral corner

Patellofemoral compartment:

  • medial patellofemoral ligament tear at the patellar and femoral attachment with nondisplaced osteochondral avulsion fracture at the inferomedial patella margin
  • fluid extending into the vastus medialis myotendinous junction
  • shallow trochlear groove
  • Hoffa fat pad edema 

Impression:

Typical findings of prior lateral patellar dislocation:

Annotated image

Key findings:

  • bone bruises of inferomedial patella (blue arrowhead) and the anterolateral femoral condyle (blue arrows)

  • patellar lateralization (blue double arrow)

  • medial patellar avulsion fracture with an unstable osteochondral fragment (purple arrow)

  • medial patellofemoral ligament with a partial tear of the patellar insertion (red arrow) and disruption of the femoral attachment (red arrowheads)

  • edema and myotendinous tear of the vastus medialis oblique (VMO) (green arrow)

  • two chondral fragments (purple arrowheads) between the anterior transverse meniscal ligament and the intercondylar groove

  • chondral lesion of the antero- and centrolateral femoral condyle (orange arrowheads) with delamination

Assessment for risk factors:

Case Discussion

This case illustrates findings typical for prior lateral patellar dislocation 1:

It also shows findings that can be associated with this condition 1-5:

There is also a decreased trochlear depth indicating trochlear dysplasia, which is a risk factor for patellofemoral instability 1,2.

The patient underwent arthrotomy with a removal of the loose intra-articular chondral fragments, lavage and debridement of the patellar and lateral femoral condyle chondral lesions and refixation of the medial patellofemoral ligament.

How to use cases

You can use Radiopaedia cases in a variety of ways to help you learn and teach.

Creating your own cases is easy.