Summary Posterolateral corner (PLC) injuries are traumatic knee injuries that are associated with lateral knee instability and usually present with a concomitant cruciate ligament injury (PCL > ACL). Diagnosis can be suspected with a knee effusion and a positive dial test but MRI studies are required for confirmation. Treatment is generally operative reconstruction of the PLC complex and the associated ligamentous injuries when present. Epidemiology Incidence Approximately 7-16% knee ligament injuries are to the posterolateral ligamentous complex only 28% of all PLC injuries are isolated login to view 1 more bullet missed PLC injury diagnosis is common cause of ACL reconstruction failure Etiology Mechanisms blow to anteromedial knee varus blow to flexed knee contact and noncontact hyperextension injuries external rotation twisting injury knee dislocation Associated injuries common peroneal nerve (15-29%) vascular injury Anatomy Posterolateral corner structures three major static stabilizers of the lateral knee lateral collateral ligament (LCL) login to view 2 more bullets popliteus tendon (PLT) popliteofibular ligament login to view 2 more bullets other static stabilizers lateral capsule thickening login to view 1 more bullet arcuate ligament (variable) fabellofibular ligament (variable) dynamic structures biceps femoris login to view 1 more bullet popliteus muscle iliotibial band (ITB) lateral head of the gastrocnemius Function popliteus works synergistically with the PCL to control external tibial rotation, varus, and posterior tibial translation popliteus and popliteofibular ligament function maximally in knee flexion to resist external rotation LCL is primary restraint to varus stress at 5° (55%) and 25° (69%) of knee flexion Definitions arcuate complex includes the static stabilizers: LCL, arcuate ligament, and popliteus tendon Lateral Structures of Knee by Layer Layer 1 Iliotibial tract, biceps common peroneal nerve lies between layer I and II Layer 2 Patellar retinaculum, patellofemoral ligament Layer 3 superficial:LCL, fabellofibular ligament lateral geniculate artery runs between deep and superficial layer deep: arcuate ligament, coronary ligament, popliteus tendon, popliteofibular ligament, capsule Classification Modified Hughston classification Modified Hughston classification Examination Findings Grade I 0-5 mm of lateral opening on varus stress 0°-5° rotational instability on dial test Sprain, no tensile failure of capsuloligamentous structures Grade II 6-10 mm of lateral opening on varus stress 6°-10° rotational instability on dial test Partial injuries with moderate ligament disruption Grade III > 10 mm of lateral opening on varus stress, no endpoint > 10° rotational instability on dial test, no endpoint Complete ligament disruption Presentation Symptoms often have instability symptoms when knee is in full extension difficulty with reciprocating stairs, pivoting, and cutting Physical exam gait exam standing varus alignment varus thrust or hyperextension thrust with ambulation varus stress varus laxity at 0° indicates both LCL and cruciate (ACL or PCL) injury varus laxity at 30° indicates LCL injury dial test > 10° external rotation asymmetry at 30° only consistent with isolated PLC injury > 10° external rotation asymmetry at 30°and 90° consistent with PLC and PCL injury external rotation recurvatum positive when lower leg falls into external rotation and recurvatum when leg suspended by toes in supine patient only identify ~10% of PLC injuries more consistent with combined ACL and PLC injuries posterolateral drawer test performed with the hip flexed 45°, knee flexed 80°, and foot is ER 15°. a combined posterior drawer and external rotation force is then applied to the knee to assess for an increase in posterolateral translation (lateral tibia externally rotates relative to lateral femoral condyle) reverse pivot shift test knee positioned at 90° and external rotation and valgus force applied to tibia as the knee is extended the tibia reduces with a palpable clunk login to view 1 more bullet peroneal nerve injury altered sensation to dorsum of foot and weak ankle dorsiflexion approximately 25% of patients have peroneal nerve dysfunction Imaging Radiographs may see avulsion fracture of the fibula (arcuate fracture ) or femoral condyle stress radiographs bilateral varus stress XR in 20° flexion side-to-side difference 2.7-4 mm = isolated LCL tear side-to-side difference > 4 mm = PLC injury long-leg standing radiographs to evaluate alignment required in cases of chronic PLC injury evaluate for triple varus alignment login to view 3 more bullets necessary to determine mechanical axis and if a proximal tibial osteotomy is necessary for correction MRI look for injury to the LCL, popliteus, and biceps tendon in acute injury may see bone bruising of medial femoral condyle and medial tibial plateau coronal oblique thin-slice through the fibular head are best at visualizing the PLC structures Treatment Nonoperative knee immobilization in full extension x4 weeks, then rehabilitation indications login to view 2 more bullets technique login to view 4 more bullets Operative PLC repair indications login to view 2 more bullets techniques login to view 4 more bullets PLC hybrid reconstruction and repair indications login to view 2 more bullets techniques login to view 18 more bullets rehabilitation login to view 6 more bullets outcomes login to view 5 more bullets PLC reconstruction, +/- ACL reconstruction, +/- PCL reconstruction, +/- HTO indications login to view 1 more bullet technique login to view 4 more bullets rehabilitation login to view 4 more bullets outcomes login to view 2 more bullets Complications Arthrofibrosis Missed PLC injury failure to identify a PLC injury will lead to failure of ACL or PCL reconstruction Peroneal nerve injury (15-29%)