RESUMEN
One of the patellar function is to protect the femoral condyle from direct blowing to knee, so it is known that ligament injuries of the knee are rare in the presence of patellar fracture. We experienced four cases of posterior cruciate ligament injury associated with patellar fracture. Unfortunately, three cases were initially neglected, and one case was identified by visualization on avulsed posterior tibial spine in plain X-ray film. We reviewed these cases and obtained several results as follows; 1. Among four cases, three cases(75%) are fractured at the lower pole of patella without displacement and one case is a longitudinal fracture. 2. We consider possible two mechanisms of this injury; first, in flexed knee, posteriorly directed force on the proximal tibia produces posterior cruciate ligament injury followed by avulsed fracture at the lower pole of patella. Second, by fall on a flexed knee, the load is sustained on the inferior pole of the patella first and continuously drives the tibia backwards producing posterior cruciate ligament injury. We recommend that all surgeon should be aware of possibility of the ligament injury in the presence of patellar fracture, especially in lower pole fracture.