Imaging Evaluation of the Patellofemoral Joint.

Background: Patellofemoral anatomic abnormalities can result in a variety of issues and require thorough clinical evaluation as well as imaging analysis to determine the cause and help guide treatment. Multiple measurements across multiple imaging modalities are used to aid in proper diagnosis. Indications: Diagnostic findings on imaging evaluation require assessment of the imaging modality, as well as the use of appropriate measurements to ensure results are reliable and accurate. Technique Description: Rotational malalignment of the knee can be evaluated with plain-film radiographs of the knee to assess for abnormal asymmetry. Computed tomography (CT) or magnetic resonance imaging (MRI) axial cuts of the knee can measure the knee rotation angle, and a full-length lower extremity CT can evaluate for rotational deformities of the femur and tibia. The quadriceps vector plays a crucial role in the patellofemoral joint. While it can be assessed on radiographs, it is best examined on CT or MRI. Important measurements here are the tibial tubercle-trochlear groove (TT-TG) distance and TT-TG angle, as well as the TT-posterior cruciate ligament distance. Patellar height is often assessed on lateral radiographs of the knee, with the Insall-Salvati and Caton-Deschamps ratios. It can also be evaluated with the patellotrochlear index and patellar tendon length, seen on sagittal MRI cuts. Trochlear dysplasia plays an important role in patellofemoral pathology. Among multiple measurements, the Dejour classification is evaluated on lateral radiographs of the knee, but it has been updated recently to include MRI criteria. Finally, patellar tilt should be evaluated using either the lateral patellofemoral angle or the patellar tilt. Results: Treatment of patellofemoral pathology relies on a detailed understanding of a patient's patellofemoral anatomy. This relies on evaluating the quality of the imaging modality used, proper selection of relevant imaging slides, and appropriate references for each measurement to have reproducible and accurate measurements. Discussion/Conclusion: Evaluation of patellofemoral instability with imaging is crucial to determine the underlying pathology. Consistent, reproducible, and accurate measurement techniques are important to obtain the correct diagnosis and determine the appropriate treatment. Patient Consent Disclosure Statement: The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.