Superior pole sleeve fracture following patellar stabilisation.

Sleeve fractures of the superior pole of the patella are rare. The importance of their diagnosis lies in the fact that the avulsed fragment contains a source of bone forming tissue which may lead to duplication or enlargement of the patella. We report a case in a 16 year old boy who underwent plication of the medial patellofemoral ligament, vastus medialis obliquus advancement and percutaneous lateral release, for recurrent instability. Interruption of the blood supply with subsequent avascular necrosis is one possible mechanism for this complication. Another more likely mechanism is that of failure of the repair and re-dislocation, which may have been contributed to by prolonged cast immobilization.