Acute PLC Background



Posterolateral complex anatomy

3 primary stabilizers (plus posterolateral capsule)


LCL / Popliteus / Popliteofibular ligament


LaPrade et al. AJSM 2003


1.  Lateral collateral ligament


Femoral attachment

- small bony depression just behind lateral epicondyle

- 1.4 mm proximal and 3 mm posterior to lateral epicondyle


Fibular attachment

- 25 mm distal to fibula styloid

- 8 mm posterior to anterior fibular head

- attaches to anterolateral fibular head



- primary varus stabilizer of the knee


2.  Popliteus tendon



- posteromedial tibial

- becomes tendon at lateral one third of the popliteal fossa



- tendon passes through capsule and hiatus in coronary ligament of lateral meniscus

- runs around lateral femoral condyle

- passes deep to LCL

- inserts into most anterior aspect of the popliteus sulcus

- always anterior and distal to LCL

- average 18.5 mm between LCL and popliteus femoral insertion



- laterally rotates the femur (important when unlocking the knee from full extension)

- also retracts the lateral meniscus in flexion to prevent entrapment of lateral meniscus

- resists external rotation of the tibia


Popliteus tendon intra-articular

Arthroscopy of right knee showing intra-articular popliteus tendon behind lateral meniscus


3.  Popliteofibular ligament


Posterolateral Corner Anatomy Popliteofibular ligament



- musculotendinous junction of the popliteus tendon



- fibular styloid



- acts as check rein to popliteus

- resists external rotation


Seebacher lateral layers of the knee


1.  Superficial


ITB, biceps femoris tendon, CPN


2.  Middle


Patella retinaculum


3.  Deep


Posterolateral capsule

LCL / Popliteus / Popliteofibular ligament


Other anatomy


Common Peroneal Nerve


Origin in bifurcation of sciatic nerve in popliteal fossa

- runs along posterior border of biceps femoris

- around neck of fibula in the fibula tunnel covered by peroneus longus

- attached to bone here by connective tissue

- then branches into deep peroneal and superficial peroneal nerve

- also gives branches to the knee joint


Lateral inferior geniculate artery


Orginates from the popliteal artery

- runs anterior to lateral head of gastrocnemius

- along superior border of popliteus muscle

- above fibular head and under LCL

- provides a branch that runs around fibula neck

- need to identify and ligate




LaPrade et al. Arthroscopy 2007


Isolated PLC injuries rare but occur


Isolated LCL injuries rare but occur


Majority of PLC injuries occur in setting of other ligament injuries (ACL / PCL / multiligament knee injury)




Twisting injury

Direct blow to anteromedial side of knee

Hyperextension injury


Associated Injuries




CPN (15%)




Significant injury

Swelling may be delayed in setting of isolated injury


Instability with extension

- knee may buckle into hyperextension with weight bearing

- may walk with knee in flexion to maintain stability




Gait / Stance


Varus thrust in gait and single leg stance

- due to ER of tibia 

- apparent varus

- flexed attitude to knee




Varus force at 30° flexion and in full extension


LCL Instability ValgusLCL Instability Varus

Examination of right knee demonstrating grade 2 instability of LCL


Grade 1

- < 5mm laxity in 30o flexion

- partial tear


Grade 2

- 5 - 10 mm laxity in flexion

- isolated injury to LCL


Grade 3

- > 10 mm laxity in flexion

- laxity in full extension

- indicates complete disruption of LCL plus a secondary restraint (ACL and or PCL)


Grade 3 LCL Grade 3 LCL

EUA of right knee demonstrating grade 3 laxity of LCL in full extension


Posterolateral Corner instability 


Dial Test 

- patient prone

- increased external rotation of tibia >10 - 15° compared to other side

- increased external rotation at 30o of knee flexion only - posterolateral corner

- increased external rotation at both 30o and 90o - PCL + posterolateral corner


Dial Test Positive at 30 degrees

Prone dial test, with increased external rotation of left knee at 30 degrees - isolated posterolateral corner


Dial test 30 degreesDial test at 30 degrees

Intraoperative dial test with patient supine.  Increased external rotation of the right foot at 30 degrees - isolated posterolateral corner


External rotation recurvatum test

- patient supine

- pick up both legs leg via great toe

- tibia hyperextends and externally rotates with injury to posterolateral corner


External rotation recurvatum

External rotation of the right knee


Posterolateral draw

- knee at 90o flexion with the foot externally rotated

- apply a posterolateral rotatory force

- excessive posterolateral tibial subluxation


Reverse Pivot Shift

- valgus force, foot externally rotated

- flexion to extension

- reduction of posteriorly subluxed lateral tibial condyle

- NB: 35% of uninjured patients positive / check normal knee




Laxity demonstrated by positive Lachmann

- posterior sag / loss of step off

- posterior drawer

- quadriceps active

- grade III posterior drawer associated with injury to the posterolateral corner as well as PCL


Posterior sag of the knee as a result of PCL injury






Often normal


Bony avulsion of Fibula Head


Avulsion of LCL and long head of biceps


LCL Bony Avulsionfibula head avulsionFibula head avulsion



Bony avulsion of Gerdy's tubercle


Avulsion of ITB


Lateral joint widening and subluxation


Knee PLC Xray Lateral Widening

Right knee in POP with opening of lateral compartment


PCL bony avulsion




Lateral collateral ligament anatomy


Don't see entire length on single MRI

- use coronal to look for origin from lateral epicondyle above popliteal insertion

- use coronal to look for insertion onto anterolateral fibular head


LCL MRI Normal Inferior PartLCL Fibular Origin


LCL MRI Normal Superior AspectLCL MRI Insertion

Normal anatomy


Knee LCL Midsubstance Tear PLC injury

Midsubstance tear of LCL


Popliteus anatomy


Don't see entire length on single images

- coronal image to see insertion onto popliteal fossa below LCL

- follow tendon around on coronal images

- watch as becomes musculo-tendinous (can often be torn here)

- muscle inserts onto posteromedial tibia


Popliteus MRIPopliteus Insertion

Normal anatomy


Popliteofibular ligament anatomy


Popliteofibular ligament MRIPopliteofibular MRI

Normal anatomy




Popliteus Avulsion MRI

Femoral avulsion of popliteus and LCL


Femoral avulsion popliteus

Femoral avulsion of popliteus


MRI LCL and Biceps Fibular Avulsion

Avulsion of LCL and biceps femoris from fibula head


Popliteus Musculotendinous Sprain

Musculotendinous injury to popliteus