Radiological evaluation of patellofemoral instability and possible causes of assessment errors

Abstract

Patellofemoral instability (PI) is the disruption of the patella’s relationship with the trochlear groove as a result of abnormal movement of the patella. To identify the presence of PI, conventional radiographs (anteroposterior, lateral, and axial or skyline views), magnetic resonance imaging, and computed tomography are used. In this study, we examined four main instability factors: Trochlear dysplasia, patella alta, tibial tuberosity–trochlear groove distance, and patellar tilt. We also briefly review some of the other assessment methods used in the quantitative and qualitative assessment of the patellofemoral joint, such as patellar size and shape, lateral trochlear inclination, trochlear depth, trochlear angle, and sulcus angle, in cases of PI. In addition, we reviewed the evaluation of coronal alignment, femoral anteversion, and tibial torsion. Possible causes of error that can be made when evaluating these factors are examined. PI is a multi-factorial problem. Many problems affecting bone structure and muscles morphologically and functionally can cause this condition. It is necessary to understand normal anatomy and biomechanics to make more accurate radiological measurements and to identify causes. Knowing the possible causes of measurement errors that may occur during radiological measurements and avoiding these pitfalls can provide a more reliable road map for treatment. This determines whether the disease will be treated medically and with rehabilitation or surgery without causing further complications.

Keywords: Patellofemoral instability; Radiological evaluation errors; Trochlear dysplasia; Patella alta; Tibial tuberosity-trochlear groove distance; Patellar tilt

Core tip: Patellofemoral instability (PI) is the disruption of the patella’s relationship with the trochlear groove. For radiological evaluation, conventional radiographs, magnetic resonance imaging, and computed tomography are used. We examine the tibial tuberosity-trochlear groove distance, patellar height, and patellar tilt measure-ments that require surgical correction and are defined as principal factors, along with other assessment methods that allow the patellofemoral joint to be evaluated qualitatively and quantitatively. We discuss the radiological assessment of patients with PI and possible misconceptions. Knowing the possible causes of measurement errors and avoiding these pitfalls can provide a more reliable road map for treatment.