The posterolateral corner (PLC) is known as the "dark side of the knee" due to its complex and variable anatomy.Its stability is provided by capsular and non-capsular structures that function as static and dynamic stabilizers.

The structures of the PLC are primarily responsible for resisting varus angulation and external tibial rotation. They also act as secondary stabilizers, in conjunction with the cruciate ligaments, to prevent anterior and posterior translation during the early phase of flexion (0°-30°) PLC injures are relatively uncommon, occurring in approximately 16% of all knee injuries. They are rarely seen in isolation, as the majority is associated with concomitant cruciate ligament tears, as well as meniscal tears and injuries to the medial ligamentous structure.

The mechanism of injuries is commonly result of a posterolaterally directed blow to the anteromedial aspect of the proximal tibia with the knee in full extension, other less common mechanisms include posterior rotatory dislocation (dashboard injury), anterior rotatory dislocation, and hyperextension injury with external rotation.

Early diagnosis of injuries to the posterolateral aspect of the knee is critical because surgical repair in the acute period is easier, and is associated with a more favorable outcome for patients. Also, failure to address instability of the PLC structures increases forces at anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) graft sites and may lead to failure of the cruciate reconstruction ,significant osteoarthritis and chronic knee instability Since introduction of MRI to musculoskeletal imaging in the early 1980s, it has proven to be an excellent technique for evaluating patients with knee problems. Its main advantages of MRI are its non-invasive nature and its high accuracy and negative predictive value in evaluating the menisci and ACL. Also it is useful in the detection and diagnosis of various traumatic, non traumatic knee abnormalities and diagnosis of occult or unsuspected bone lesions. It can help in the selection of those patients who need therapeutic arthroscopy.

Assessment of PLC injures is usually made clinically , including several physical examination maneuvers by orthopedic physician ; such as posterolateral drawer test, dial test, reverse pivot shift test, external rotation recurvatum test and varus stress test.

Despite these several tests, in 72% of cases they are not identified in his initial presentation, which demonstrates the difficulty of clinical diagnosis.

Thus, it is important to use additional tests for the diagnosis of posterolateral corner injury. The medical literature demonstrates that MRI has an accuracy of up to 95% for identifying major injury PLC structures, namely, lesions of the lateral collateral ligament (LCL), popliteus muscle tendon (PMT) and poplitealfibular ligament (PFL).

For better visualization of the PLC structures, an oblique coronal T2 cut should be performed. It provides an accurate and detailed evaluation of the posterolateral corner structures of the knee.

As PLC injures may be difficult to be assessed clinically because of associated and coexisting injuries at the knee, so MRI can provide vital information regarding the status of the posterolateral corner, thus enabling good surgical planning and more effective treatment.

Inclusion Criteria:

1. Patients have positive tests of posterolateral corner instability by clinical examination.
2. Patients who suspected by Plain X-ray to have posterolateral corner injury.

Exclusion Criteria:

1. Patients whom previously underwent arthroscopy or surgically intervention to knee joint.
2. Patients with history of fracture repaired by metal plates or screws.
3. Patients have phobia of indoor places.
4. Patients with contraindication to MRI like intra-cerebral aneurysmal clips, cardiac pacemaker, and metallic foreign body at region of examination

patients with posterolateral corner trauma of the knee