Two Cases of Inferior Dislocation of the Patella with Impaction into the Femoral Trochlea of Osteophytes on the Superior Pole of the Patella

Traumatic dislocation of the patella is classified as lateral, medial, or intra-articular according to the direction of dislocation. Lateral dislocation is the most common type of patellar dislocation, and intra-articular dislocation is rare. Intra-articular dislocation is classified as superior, inferior, or vertical dislocation. Inferior dislocation is categorized as Type I, which occurs in young people, and Type II, which occurs in the elderly. In Type II, osteophytes on the superior pole of the patellar are believed to become entrapped in the intercondylar notch, dislocating the patella inferiorly. These were two extremely rare cases of inferior dislocation of the patella in elderly people. The mechanism involved was considered to be the exertion of sudden upward traction on the patella due to the muscular force of the quadriceps when the knee was flexed, causing osteophytes on the superior pole of the patella to become impacted into the femoral trochlea. Dislocations were successfully reduced without anesthesia, and osteophyte resection or complete osteophyte fracture during reduction meant that there was no recurrence of the dislocation.