لخّصلي

Introduction
The study of posterior cruciate ligament (PCL) injuries has attracted much less interest in the orthopaedic literature than studies of the anterior cruciate ligament (ACL) However, clinicians have become increasingly aware of the importance of the PCL in maintaining normal knee kinematics and function There have been numerous recent studies of the complex anatomy and functional mechanics of the PCL, but our knowledge regarding PCL injuries is still limited Controversies still exist with regard to the incidence, diagnosis and treatment of PCL injuries]. The reported incidence of PCL ruptures ranges between 1% and 44% of all acute knee ligament injuries This variability is probably due to differences in the patient populations studied, as PCL injury rates are likely to vary when comparing polytraumatized patients to an athletic population

Numerous clinical tests are available for detecting and grading PCL lesions and most PCL injuries can be diagnosed in the acute phase with a detailed history and a thorough clinical examination [4, 9, 27, 29]. Nevertheless, in the past many PCL ruptures have frequently been missed in the acute phase and were first diagnosed in the chronic situation In many cases the PCL injury is missed despite typical injury mechanisms and symptoms However, an accurate diagnosis of the acute injury is critical to establishing a rational treatment algorithm, whether conservative or surgical Furthermore, it is critical to distinguish between PCL lesions that are isolated and those combined with other ligament injuries, as this variable will directly affect the treatment and prognosis To our knowledge, there has been no previous study of the demographic data and PCL injury mechanisms in a large patient population. Therefore, we retrospectively analysed our patient population to define the epidemiology of PCL lesions and to improve understanding of the typical injury mechanisms in acute and chronic injuries. We hope this knowledge will enhance the clinician's ability to recognize situations in which injuries of the PCL should be suspected, and aid in an accurate and timely diagnosis.

Patients and methods
Between 1993 and 1999, 587 patients with acute and chronic PCL-deficient knees were seen at our institution. The diagnosis was made using a detailed history in connection with a thorough physical examination and posterior stress-radiographs. To diagnose PCL insufficiency, the posterior drawer test and the posterior sag test were done. Assessment of the posterolateral corner was made with the external rotation test at 30° and 90° degrees of knee flexion and the posterolateral drawer test [3, 31]. General inclusion criteria for the study included a PCL tear confirmed by clinical examination and stress-radiography. A side-to-side difference (SSD) of posterior tibial displacement of ≥5 mm on posterior stress-radiographs in 90° of flexion was considered diagnostic for a PCL tear according to the amount of laxity on posterior drawer testing

At initial presentation all patients had bilateral posterior stress-radiographs taken in 90° of knee flexion with an applied force of 15 kp using the Telos device (Telos, Marburg, Germany) (Fig. 1). The patient lies in the lateral decubitus position with the involved limb on the table. The limb is positioned in neutral rotation and the load applied to the anterior proximal tibia at the level of the tibial tubercle. A lateral radiograph is taken with the knee flexed approximately 90°. The lateral radiograph is taken from medial to lateral with a standard tube-to-cassette distance of 1.15 m. Radiographs were performed only by experienced orthopaedic radiologic technicians. The stress-radiographs were evaluated according to the technique described by Jacobsen After establishing a tibia plateau line, perpendicular lines tangential to the most posterior aspects of the medial and lateral tibial plateaux and the femoral condyles were drawn. With rotation of the limb, the midpoint between the two corresponding lines was established, and these landmarks were then used to measure skeletal displacement of the knee Patients who had MRI images that indicated a rupture of the PCL but had a SSD of posterior displacement of less than 5 mm were determined to have partial ruptures and were not included in this study. Of the 587 patients, 494 met the inclusion criteria and formed the study group. Patients were further subdivided into groups concerning the duration of PCL insufficiency. The following groups were defined, based on the time between injury and first visit at our institution
Furthermore, we differentiated between an isolated PCL lesion versus a combined posterior instability pattern. To define these subgroups, a SSD of 5–12 mm of posterior tibial displacement on stress-radiographs was classified as an isolated injury, whereas a displacement of more than 12 mm was considered to be a combined injury

For statistical analysis the chi-square test, the Mann-Whitney U Wilcoxon rank sum test, and the Kruskal-Wallis H test for independent values was used. The significance level was set at p