[Avulsion fractures of the lower pole of the patella]

Fractures of the lower pole of the patella are rare and occur typically in children. In these types of fractures an extensive sleeve of cartilage is pulled off with a small bony fragment. The so-called sleeve fractures are often overlooked in plain radiographs. We describe the operative treatment and outcomes in two patients with sleeve fractures, one receiving early and one delayed treatment.A 12-year-old boy (case 1) sustained an indirect injury to the left knee while playing ball. Clinical examination showed a lag of active extension of the left knee without decrease in passive range of motion. At 9 years of age, a 12-year-old girl (case 2) sustained a direct blunt trauma to her right knee while playing ball. The lesion of the lower pole of the patella was not diagnosed in time. During the following 3 years a lag of extension of the right knee developed.The sleeve fracture diagnosed early was treated by open reduction and internal fixation with transosseous suturing. At the 6-month follow-up the knee had regained full range of motion. The sleeve fracture diagnosed late showed a nonunion of the patella resulting in a lag of extension. Even after 3 years a shortening osteotomy of the patella resulted in full range of motion of the right knee.