*3.3.10 Magnetic resonance imaging*

Magnetic resonance imaging (MRI) combines the accuracy of osseous measurements made on CT scan with the ability to visualize the soft tissues. Furthermore, MR imaging can detect pathologies such as, articular cartilage lesion of the patella and/or the femoral condyle. Advantages of the MRI include ability to obtain images in multiple planes, better soft tissue resolution, and no risk of exposure to radiation. Sallay et al. [72] have reported the pathoanatomic features of patellar dislocations using MRI. The location of the injury was confirmed by surgical exploration. In their study, MRI revealed effusion in all 23 patients (100%), tears of the femoral attachment of the MPFL in 20 patients (87%), increased signal intensity and retraction of the vastus medialis muscle in 18 patients (78%), a bone bruise in the lateral femoral condyle in 20 (87%), and a bone bruise in the medial patella in 7 (30%). Arthroscopic examination revealed osteochondral lesions involving the patella and the lateral femoral condyle in 68% of cases. Open surgical exploration revealed tears of the MPFL off the femur in 15 of 16 patients (94%). Sallay et al. [72] also noted that the location of the bone bruise on the lateral femoral condyle was slightly anterior and superior to the typical bone bruise seen after an acute anterior cruciate

**Figure 5.**

*(A). Axial MR image of the knee showing a normal MPFL. (B). Axial MR image of the knee demonstrating an avulsion of the MPFL from its femoral attachment. Reprinted with permission from Boden et al. [50].*

ligament injury. An axial MRI image of the knee showing an avulsion of the MPFL from its femoral attachment is shown in **Figure 5**.

Injury to the VMO, which lies superficial to the MPFL, frequently presents as edema, hemorrhage, and/or elevation of the muscle away from the medial femoral condyle [73, 74]. Approximately 50–80% of injured MPFLs are disrupted at their femoral origin [73–75].
