Acute PLC Background

Anatomy

 

Posterolateral complex anatomy

3 primary stabilizers (plus posterolateral capsule)

 

LCL / Popliteus / Popliteofibular ligament

 

Laprade et al. AJSM 2003

https://pubmed.ncbi.nlm.nih.gov/14623649/

 

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

 

Action

- primary varus stabilizer of the knee

 

2.  Popliteus tendon

Origin

- posteromedial tibial

- becomes tendon at lateral one third of the popliteal fossa

 

Insertion

- 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

 

Action

- 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

 

3.  Popliteofibular ligament

 

Posterolateral Corner Anatomy Popliteofibular ligament

 

Origin

- musculotendinous junction of the popliteus tendon

 

Insertion

- fibular styloid

 

Action

- 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

 

Orgin 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

 

Incidence

 

LaPrade et al. Arthroscopy 2007

https://pubmed.ncbi.nlm.nih.gov/18063179/

 

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)

 

Mechanism

 

Twisting injury

Direct blow to anteromedial side of knee

Hyperextension injury

 

Associated Injuries

 

PCL

ACL

CPN (15%)

 

History

 

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

 

Examination

 

Gait / Stance

 

Varus thrust in gait and single leg stance

- due to ER of tibia 

- apparent varus

- flexed attitude to knee

 

LCL

 

Varus force at 30° flexion and in full extension

 

LCL Instability ValgusLCL Instability Varus

 

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

 

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 degreesDial test 30 degreesDial test at 30 degrees

 

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

 

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

 

PCL 

 

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

 

 

ACL

 

X-ray

 

Often normal

 

Bony avulsion of Fibula Head

 

Avulsion of LCL and long head of biceps

 

LCL Bony Avulsion

 

Bony avulsion of Gerdy's tubercle

 

Avulsion of ITB

 

Lateral joint widening and subluxation

 

Knee PLC Xray Lateral Widening

 

PCL bony avulsion

 

MRI 

 

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

 

Injury

 

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