Irreducible Acute Patellar Dislocation due to a New Anatomical Variant - the Notched Patella.

Irreducible patella dislocations are rare and are usually associated with complex mechanisms. The authors report the clinical case of an irreducible lateral patellar dislocation due to an anatomical variant. The authors assisted a 16-year-old patient who presented with a lateral patella dislocation that was impossible to reduce by closed manipulation, even under general anesthesia. During the imaging study, the computed tomography (CT) exam showed a notch in the medial facet of the patella, impacted in the lateral condyle, which prevented the reduction. This anatomical variant was later confirmed during surgery. In a bilateral follow-up CT, this variant was also present in the contralateral, normal knee, excluding traumatic reshaping as the reason for this patellar notch. The authors used a medial parapatellar approach for open reduction of the dislocation and to repair the medial retinaculum. According to Wiberg, there are three different patella types. The authors describe a variation of type III patella with a notch in the medial border that is not included in the previous classification. They emphasize the importance of a CT study in the presence of an irreducible dislocation and the recognition of this anatomical variant of the patella, as further aggressive maneuvers have proven to be unsuccessful. Open reduction appears to be the best option in this scenario.