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

Abstract Irreducible patella dislocations are rare and are usually associated with complex mechanisms. Theauthors report the clinical case of an irreducible lateral patellardislocationdueto an anatomical variant. The authors assisted a 16-year-old patient who presented with a lateral patella dislocation that was impossible to reduceby closedmanipulation, 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 themedial retinaculum. According to Wiberg, there are three different patella types. The authors describe a variation of type III patellawith a notch inthemedial border that is not included in the previous classification. They emphasize the importance of a CTstudy 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