Patellofemoral instability: Anatomy, imaging techniques, and clinically relevant measurements

The patellofemoral (PF) joint plays an integral role in knee biomechanics. Disorders of the PF joint are prevalent and a common source of anterior knee pain, particularly in younger and active patients. Abnormalities related to patellar tracking can lead to recurrent lateral patellar dislocation, early degenerative changes, and poor clinical outcomes if not detected and treated appropriately. Therefore, early recognition of PF instability is imperative to preserving joint function and improving long-term patient outcomes. Several alignment and morphological abnormalities are known risk factors that predispose patients to PF instability, including patellar malalignment, trochlear dysplasia, tibial tubercle lateralization, genu valgus, and rotational deformities. Imaging plays a key role in identifying these abnormalities and other osteoarticular and soft tissue pathology of the PF joint. Additionally, several quantitative measurements performed on imaging provide objective information on patellar alignment and tracking, further aiding clinicians with diagnosis and treatment planning. A consistent and standardized approach to the quantitative imaging evaluation of the PF joint is necessary for accurate reporting of measurements and imaging findings. This article highlights essential PF joint anatomy, current and evolving imaging techniques, and clinically relevant measurements for the evaluation of patients with suspected PF instability.