Background: The treatment of symptomatic posterior cruciate ligament injuries of the knee is controversial. Identification of concomitant injuries of the posterolateral corner is important to optimize surgical and clinical outcomes, although this diagnosis is sometimes difficult. The purpose of this study was to determine the physical examination and stress radiography parameters of isolated injuries of the posterior cruciate ligament and combined injuries of the posterior cruciate ligament and posterolateral corner. Our hypothesis was that Grade-3 posterior drawer laxity is an indicator of a concomitant injury of the posterolateral corner.

Methods: Ten pairs of cadaver knees (a total of twenty knees) were evaluated with posterior drawer testing, dial testing, and stress radiography. Stress radiography was performed by applying a 200-N posterior drawer at 90° of knee flexion. The knees were tested while intact and then retested following the sequential resection of the posterior cruciate ligament followed by the posterolateral corner structures.

Results: All intact specimens were rated as Grade 0 on posterior drawer testing. Sectioning of the posterior cruciate ligament resulted in Grade-2 posterior drawer in all specimens. The additional resection of the posterolateral corner resulted in Grade-3 posterior drawer in all specimens. Dial testing of the intact knees resulted in a mean (and standard error) of 10.5° ± 1.0° and 10.5° ± 0.80° of external rotation at 30° and 90°, respectively. This increased significantly to 15.1° ± 1.1° and 16.2° ± 0.89°, respectively, following sectioning of the posterior cruciate ligament (p < 0.05). After resection of the posterolateral corner, rotation was further increased to a mean of 21.6° ± 1.5° at 30° and 27.5° ± 1.6° at 90° (p < 0.05). On stress radiography, the average posterior displacements measured 2.9 ± 0.5 mm in the intact specimens, 12.7 ± 1.0 mm after resection of the posterior cruciate ligament, and 22.3 ± 1.6 mm after the additional resection of the posterolateral corner (p < 0.05). The corrected posterior displacement, calculated by subtracting the displacement in the intact knees, was 9.8 mm after resection of the posterior cruciate ligament and 19.4 mm after the additional resection of the posterolateral corner.

Conclusions: A grade of 3 on posterior drawer testing and >10 mm of posterior tibial translation on stress radiography correlate with the presence of a posterolateral corner injury in addition to a complete disruption of the posterior cruciate ligament.

Clinical Relevance: Detection of grade-3 posterior drawer on physical examination should alert the examiner to the presence of a posterolateral corner injury.