Bilateral varus stress AP radiographs comparing the injured leg to the normal side are useful in assessing the lateral joint space for opening after a potential injury. More than a 2.7 mm increase between sides indicates a fibular collateral ligament tear, while greater than 4.0 mm indicates with a grade III posterolateral knee injury. Posterior stress radiographs taken with the patient kneeling show the amount of posterior tibial translation in both knees and are helpful to diagnose PCL insufficiency and combined injuries. Between 0–2 mm increased posterior translation between the affected and healthy knees is normal, 2–7 mm indicates a partial tear, 8–11 mm suggests a complete tear and greater than 12 mm suggests a combined PCL and PLC injury. MRI High quality MRI images (1.5 T magnet or higher ) of the knee can be extremely useful to diagnose injuries to the posterolateral corner and other major structures of the knee. While the standard coronal, sagittal and axial films are useful, thin slice (2 mm ) coronal oblique images should also be obtained when looking for PLC injuries. Coronal oblique images should include the fibular head and styloid to allow for evaluation of the FCL and popliteus tendon. Specialized tests In addition to a complete physical examination of the lower extremity, there are a set of specialized tests that must be synthesized to specifically check for injuries to the posterolateral corner. It is always important when evaluating an extremity for injury to compare it with the normal side to make sure you are not seeing a normal variation within that patient: External Rotation Recurvatum Test - One of the first tests developed to assess the PLC, the external rotation recurvatum test is performed with the patient lying supine. The practitioner stabilizes the distal thigh with one hand while lifting the great toe with the other. The injured side is compared to the healthy one and a positive test is indicated by an increased amount of recurvatum, or hyperextension, in the affected knee. Increased recurvatum indicates possible combined injuries to the posterolateral corner and cruciate ligaments. The increase on recurvatum is best reported as the heel height off the examining table. Varus stress test at 0° and 30° - Varus stress testing is accomplished while the patient is lying supine on an examination table. The physician supports the thigh against the side of the exam table and applies a varus