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 usually combined with cruciate ligament injury (PCL > ACL) 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) most anterior structure inserting on the fibular head primary varus stabilizer of the knee popliteus tendon (PLT) popliteofibular ligament originates at the musculotendinous junction of the popliteus anterior and posterior divisions other static stabilizers lateral capsule thickening meniscofemoral and meniscotibial ligaments arcuate ligament (variable) fabellofibular ligament (variable) dynamic structures biceps femoris inserts on the posterior aspect of the fibula posterior to LCL 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 tibia reduces from a posterior subluxed position at ~20° of flexion to a reduced position in full extension (reduction force from IT band transitioning from a flexor to an extensor of the knee) 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 primary varus = tibiofemoral malalignment secondary varus = LCL deficiency with increased lateral opening triple varus = remaining PLC deficient, overall varus recurvatum alignment 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 grade I PLC injury isolated midsubstance grade II injury technique hinged knee brace locked in extension x4 weeks followed by progressive functional rehabilitation quad strengthening return to sports in 8 weeks Operative PLC repair indications isolated acute grade II PLC avulsion injuries midsubstance repair have 40% failure rate following repair techniques repair of LCL, popliteus tendon and/or popliteofibular ligament should be performed if structures can be anatomically reduced to their attachment site otherwise perform reconstruction augment PLC repair with free graft if repair tenuous avulsion fracture of fibular head can be treated with screws or suture anchors PLC hybrid reconstruction and repair indications grade III midsubstance injuries avulsion injuries where repair is not possible or tissie is poor quality techniques goal is to reconstruct LCL and the popliteofibular ligament using a free tendon graft (semitendinosus or achilles) fibular-based reconstruction (Larson) soft tissue graft passed through bone tunnel in fibular head limbs are then crossed to create figure-of-eight and fixed to lateral femur to a single tunnel trans-tibial double-bundle reconstruction split achilles tendon is fixed to isometric point of the femoral epicondyle one tibia-based limb and one fibula-based limb fibula-limb is fixed to the fibular head with a bone tunnel and transosseous sutures to reconstruct the LCL tibia-limb is brought through the posterior tibia to reconstruct the popliteofibular ligament LaPrade anatomic reconstruction two soft tissue grafts graft #1 reconstructs the LCL and PFL proximal attachment site at anatomic femoral LCL attachment through the fibular head lateral to medial docking into the tibial tunnel posterior to anterior with graft #2 graft #2 reconstructs the popliteus tendon proximal attachment site at the anatomic popliteus tendon attachment docking into the tibial tunnel posterior to anterior with graft #1 rehabilitation hinged knee brace, nonweightbearing for 6 weeks range of motion protocols differ between surgeons some advocate for passive ROM immediately 0-90° others immobilize for 2 weeks, then begin motion at 6 weeks, begin weightbearing and closed-chain strenghtening return to activities / sports ~ 6 to 9 months outcomes operative treatment has improved outcomes compared to nonoperative treatment repair has higher failure rate than reconstruction particularly for midsubstance injuries, but also for soft tissue avulsions improved outcomes with early treatment anatomic reconstruction restores rotatory stability, but not all varus stability on stress testing PLC reconstruction, +/- ACL reconstruction, +/- PCL reconstruction, +/- HTO indications acute and chronic combined ligament injuries technique PLC reconstruction should be performed at same time or prior to (as staged procedure) ACL or PCL to prevent early cruciate failure valgus high tibial osteotomy indicated in patients with varus mechanical alignment failure to correct bony alignment jeopardizes ACL and PLC reconstruction success rehabilitation postoperatively immobilize and make protected weight bearing for 4 weeks (long leg casts may control leg external rotation better than brace) begin passive ROM at 4 weeks to avoid arthrofibrosis. avoid active hamstring exercises as they will stress the PLC full active extension is allowed outcomes reconstructions have less revision rates and better outcome scores than ligament repair ACL reconstruction + PLC repair 33% achieved IKDC grade A or B compared to 88% of patients who underwent ACL + PLC reconstruction 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%)