Imaging of the patellofemoral joint

The patellofemoral articulation is the product of a complex interaction of static, dynamic and active stabilizers. Their function is based on various anatomical structures of the patellofemoral joint (PFJ). The PFJ is covered by a particularly thick cartilage surface, the condition of which can be both the cause and consequence of several patellofemoral pathologies. Until today, native radiography is an important foundation in the diagnostics of the PFJ. It is used to identify acute sequelae of trauma and for the assessment of the patellar height relative to the femoral trochlea. In addition, the standing long leg radiography in the frontal plane should be part of the standard diagnostics in order to detect valgus deformities of the leg axis or indirect signs for torsional deformities. Particularly in the latter case, computed tomography (CT) plays an important role to analyze femoral and tibial torsion (torsional CT). Furthermore, CT is the method of choice for the visualization of complex fracture patterns; however, the gold standard in patellofemoral diagnostics is so far magnetic resonance imaging (MRI). MRI enables a precise assessment of the patellofemoral joint cartilage as well as the visualization of the relevant anatomical structures. In the case of a clinically diagnosed patellofemoral maltracking (PM), the identification of corresponding (static) anatomical risk factors is fundamental. Furthermore, novel dynamic MRI sequences enable the quantification of patellar tracking under the influence of active muscle contraction, thus enabling a direct identification of PM. Other imaging modalities, such as single proton emission computed tomography (SPECT), are reserved for special situations.