What are the main medial patellar stabilizers?
The medial patellofemoral complex with the medial patellofemoral ligament, the medial retinaculum and the medial vastus obliquus (VMO).
What are considered as risk factors for patellofemoral instability?
Patella alta, trochlear dysplasia, increased TT-TG distance.
What should the finding of a chondral or osteochondral lesion prompt the radiologist to?
To search for loose intra-articular chondral fragments.
Where should chondral lesions be mostly suspected in patellar dislocations?
In the patellofemoral compartment most often medial patellar facet and patellar dome less commonly the trochlea or lateral femoral condyle.
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 oedema
- 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 oedema
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