Patellar dislocation with chondral injury

Case contributed by Joachim Feger
Diagnosis certain

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:

  • medial patellofemoral ligament tear at the patellar and femoral attachment with osteochondral avulsion fracture at the inferomedial patellar margin
  • two intraarticular chondral fragments
  • extensive chondral lesion of the antero- and centrolateral femoral condyle
  • traumatic changes of the Hoffa fat pad
  • decreased trochlear depth indicating trochlear dysplasia
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:

  • Insall-Salvati index ≈ 1,3 - borderline

  • decreased trochlear depth (<3mm)

  • lateral trochlear inclination (LTI) and trochlear facet ratio within normal limits

  • TT-TG < 15mm

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.

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