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Understanding the natural history of lateral patellar dislocations (LPD) is to understand the risk of reinjury. There are many elements that may factor in evaluating a “risk equation,” among them sport, age, and level of fitness. However, at the core of evaluating risk is understanding the unique role of one’s own anatomy in the risk of reinjury. This chapter will be a brief review of the present state of the influence of anatomic risk factors in the risk of reinjury after a primary LPD.

A patellar dislocation is most likely a result of a number of anatomic and physiologic factors causing a failure of the extensor mechanism to deliver the patella into the femoral sulcus. The Lyon group has reported this experience in several articles [5,7,9,17–20]. In the episodic patellar dislocation (EPD) patient population, several morphological anomalies have been identified that facilitate or allow patellar dislocation [18]. The radiographic examination will detect, in more than 96% of cases, at least one of the four following features in EPD group: (1) trochlear dysplasia, (2) Patella Alta, (3) tibial tubercle-trochlear groove distance (TT-TG) >20 mm, and (4) patellar tilt >20°. The aim of the distal realignment is to correct one or two identifiable “main factors” for EPD, while the “fundamental factor,” i.e., trochlear dysplasia, itself may not be corrected. In order to lower or medialize the distal extensor mechanism, different surgical techniques have been proposed and described. They all have in common that these techniques transfer the distal insertion of the patellar tendon [3,15,16].