BACKGROUNDPatellar fracture and cruciate ligament injury are a common consequence of traumatic knee injury. Patellar fracture combined with cruciate ligament injury is rarely reported, although the mechanisms of two things are similar. This study aimed to evaluate the incidence of closed patella fracture combined with cruciate ligament injury.

METHODSFrom 2012 March 1 to June 30, magnetic resonance images of 60 patients with unilateral closed patellar fracture were studied in our institution. The mean age of the patients at presentation was 40.2 years (range, 13-64 years) and 48 patients were men. First, patients were divided according to the cause of injury. Twenty-eight patients had high-energy trauma from a falling injury or motor vehicle accident, and 32 patients had low-energy trauma resulting from a tumbling injury. Second, according to the fracture pattern, 31 patients had a transverse fracture and 29 patients had a comminuted fracture.

RESULTSWe found seven cases of closed patellar fracture combined with cruciate ligament injury among 60 patients, including two cases of a completely ruptured posterior cruciate ligament, two with a partially torn posterior cruciate ligament, and three with a partially torn anterior cruciate ligament. The percentage of this combined injury was 11.6% (7/60). The incidence of a combined injury of the cruciate ligament with a comminuted fracture (6/29, 20.7%) was significantly higher than that with a transverse fracture (1/31, 3.2%, P < 0.05). The most common mechanism of injury in patellar fracture combined with cruciate ligament injury was high-energy trauma from road traffic accidents (94%), whereas in the patellar fracture alone, it was tumbling (62%). The incidence of combined injury with high-energy trauma (6/28, 21.4%) was significantly higher than that with low-energy trauma (1/32, 3.1%, P < 0.05).

CONCLUSIONSThese data suggest that high-energy trauma often results in a comminuted patellar fracture, which is often combined with cruciate ligament injury. Traffic accidents are the main risk factor for this combined injury. Understanding the relationship between patellar fracture and cruciate ligament injury for diagnosis and treatment is important.