I'd like to thank John Kelly for the invitation. I have no disclosures. Imaging is essential for the diagnosis of many patellofemoral disorders, and there are three main imaging modalities that we use, conventional radiographs, MRI, and CT scan. Given the subjects of this session, I decided to focus on imaging of patellofemoral instability and dislocation and discuss how we can look at the four classic predisposing factors to patellofemoral instability, namely patella alta, trochlear dysplasia, abnormal TTTG distance, and patellar tilt. Radiographs should be the first line imaging modality. We have our three standard views. We'll look at these more closely. The frontal view is limited for the assessment of patellofemoral disease, but we may see extreme malalignments such as this lateral patellar dislocation. Beware of poor technique. This looks like it's dislocated. However, it is not. The film is oblique with no overlap of the fibula and tibia here. The lateral film is done with a mild flexion. The posterior condyles should be perfectly superimposed and not offset like here. This is gonna be important for our measurements. The axial or sunrise view may be done in various degrees of flexion. Ensure that the x-ray beam is tangent to the joint space, especially when we're gonna do measurements. This is suboptimal here. The lateral view is used to measure, to assess for patella alta. These are the three most commonly used methods. These are the three most commonly used methods. Each has their limitations and advantages. One meta-analysis showed that most orthopedic surgeons in their clinical practice use either in-cell cell body or caton de champ and more commonly in-cell cell body. So we're looking basically for the ratio to be, for A over B to be greater. Trochlear dysplasia is probably, or is the single most important factor affecting patellofemoral disease and stability. And a normal trochlea has a somewhat of a V shape with a well-defined groove. Here are some examples of a dysplasia with a shallow groove, asymmetric facets, and sometimes a frankly convex patellar or trochlear groove. Trochlear dysplasia can also be assessed by x-ray. This is a zoomed up view of the lateral x-ray. Anteriorly, we have the two superimposed medial and lateral trochlear facets. And the line immediately posterior to that is the trough of the trochlear groove. And note in this patient with dysplasia, we do have that posterior line, which is the trochlear groove. Very close to it, however, is a shallow trochlear facet, likely the medial, and another line showing a shallow lateral facet with decreased distance here. In addition, we may see the so-called crossover sign where the floor of the trochlear groove crosses the anterior femoral line, present in 96% said of a trochlear dysplasia patient. In addition, we have information on the patella. Here we have this radiodense line corresponds to the superimposition of the medial and lateral patellar facets. Posterior to that is the patellar apex. And note here how these facets are aligned. This is abnormal. This is due to lateral patellar tilt. Lateral patellar tilt is more typically assessed on the sunrise view. Normally, this angle drawn here opens laterally. In subluxors, it is parallel or medial facing. The TTTG has been discussed. It's also a measure of the, or it is a measure of lateralization of the tibial tuberosity. This can be looked at, measured on CT or MR. It's important to discuss the medial soft tissue stabilizers. The most important is, of course, the medial patellofemoral ligament, which extends from between the medial epicondyle and the ductal tubercle to the superior medial patella, immediately adjacent or inferior to the VMO, vastus medialis oblique muscle. However, the anatomy is more complex than that. There are also fibers going to the quadricep tendon. And on MR, we can see here, as we go from cranial to caudal, ligaments are of low signal intensity on all sequences, so they're dark on all the sequences. Here, when you're at the cut where you see muscle, you are probably at the level of the MPFL or MPF complex. And here, you still see a little bit of muscle fibers. That's probably also MPFL. And more inferiorly, when you're frankly at the MCL level, you're probably out of the MPFL and into the retinacular structures. Okay, here's an example of an acute lateral patellar dislocation. You have the typical coup-contre-coup injuries of the medial patella and this characteristic rectangular shape of edema of the lateral femoral condyle, a more acute case with a frankly disrupted MPFL, definitely at the femoral side and partially at the patellar side, extensive edema and joint effusion. Another patient, 12 years old. Here, we have an osseous avulsion of the patella with disruption, not so much of the femoral attachment, but the patellar attachment of the MPFL. We're quite high up in the knee here. Note the shallow trochlear groove. And we have that characteristic rectangular shape of the contusion of the lateral femoral condyle. For your patients, it's very important to look at assessment of cartilage. What lesions have they, especially in the dislocators, do they have cartilage lesions? On a good MRI, you want the axial FAT-SAT PD sequence. You don't want a T1 or something like that. On a nice study, you can see a nice gray cartilage here. The earliest stage of chondrosis is signal change, like shown here. Grade two is partial thickness fissures that don't extend to the subchondral bone. And then the full thickness defects, as shown here, in the patellar apex and in the trochlea, with subchondral cyst-like marrow lesions, generally denote full thickness defects. The trochlea, don't forget to use the sagittal plane to assess the trochlear. There's a bit of a blind spot sometimes on the axial MR images for the trochlear cartilage. This is what normal trochlear cartilage looks like. This is a recurrent dislocator, severe cartilage disease, both on the patella and lateral trochlear facet. Note the impingement here of the FAT pad. So ensure you have adequate x-ray technique, and you can evaluate on imaging these four factors predisposing to patellofemoral instability. Thank you for your attention. Thank you.

imaging

diagnosis

patellofemoral disorders

patellofemoral instability

dislocation