Acute combined posterior cruciate and posterolateral instability of the knee.

This report concerns 13 consecutive patients (13 knees) who underwent operative treatment for acute combined posterior cruciate and posterolateral instability due to combined injury to the posterior cruciate ligament and the arcuate ligament complex. Our purpose was to examine the method of diagnosis and the results in these patients. There were 12 males and 1 female (average age, 26 years). Five patients were injured in a motor vehicle accident, four in sports activities, and four in nonsports activities. The mechanism of injury was an anteromedial blow to the flexed knee in six patients, a fall onto the knee in two, and unknown in five patients. Eleven patients were available for follow-up evaluation (average, 56 months), and in each the result was rated as good, fair, or poor. In 10 patients (90%) the results were rated as good subjectively, in 11 (100%) as good functionally, and in 8 (73%) as good objectively. Injury to both the posterior cruciate ligament and the arcuate ligament complex can result from rotational force that can be due to a blow to the anteromedial aspect of the knee. Diagnosis can be made by a combined positive response to the posterior drawer test, the anterior drawer test performed with the tibia in internal rotation, the abduction and adduction stress tests performed with the knee in full extension, the posterolateral drawer test, and the external rotation-recurvatum test. In a knee with concomitant injury to the posterior cruciate ligament and the arcuate ligament complex that requires surgical repair, all injured structures should be explored and repaired to ensure a subjectively, objectively, and functionally good result.