Posterolateral rotatory instability (PLRI) of the knee is an uncommon injury pattern that may result in significant degrees of functional disability. Usually accompanied by other instabilities, it’s easily missed, misdiagnosed and mistreated. This injury complex can be a challenging diagnostic and therapeutic problem for the orthopaedic surgeon. PLRI can either be as an isolated injury or in association with anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) injuries. O’Brien et al. (1991) documented that one cause of failure of ACL reconstruction is unrecognized posterolateral knee instability. Proper evaluation of these injuries requires a knowledge of the anatomy and biomechanics of the posterolateral corner. Accurate diagnosis of all knee ligaments pathology will allow appropriate planning for the surgical treatment of isolated posterolateral knee instability and combined instability patterns. Evaluation of all ligaments of the knee, including the medial collateral ligament (MCL), ACL, and PCL as well as the integrity of the menisci and also complete neurovascular examination is mandatory. The distinction between isolated and combined posterolateral corner injuries is crucial both for treatment and prognosis. There has been no optimal procedure for reconstructing the posterolateral corner in situations where direct primary repair is not feasible. This was reflected by the large number of procedures described.