Patellar Instability: Diagnostic Workup

The patella is a sesamoid bone that comprises a vital component of the extensor mechanism of the knee. It has static and dynamic restraints that differ throughout range of motion of the knee. Tracking, and potentially maltracking, are impacted additionally by the bony anatomy of the pelvis, femur, and tibia.

Evaluation of patients with patellofemoral instability warrants consideration of each of these nuanced arenas of tracking. The diagnostic workup must be based on a thorough understanding of anatomy, which guides focused physical examination maneuvers that are not always completed in the standard knee examination of the adult or pediatric patient.

A complete patellofemoral instability examination requires evaluation of femoral anteversion (while prone), tibial external torsion (thigh foot angle), knee range of motion (J sign), patellar evaluation (to assess apprehension and translation), standing examination, and a gait and foot progression analysis.

The key components of a patellofemoral physical examination allow a provider to assess all parameters involved in the patellofemoral pathology.

In conjunction with these anatomy-informed physical examination maneuvers, the provider can also evaluate radiographic and cross-sectional imaging, which are vital to informed surgical decision-making.

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