Acute PLC Background

Anatomy

 

Posterolateral Complex (3 components)

 

Posterolateral complex anatomyPosterolateral corner anatomy 2Posterolateral Corner Anatomy

 

1.  Lateral collateral ligament

 

Lateral epicondyle to superior fibula head

 

MRI Anatomy

- don't see entire length on single MRI

- need 2 or more images

- inserts superior to popliteus

 

LCL MRI Normal Inferior PartLCL Fibular Origin

 

LCL MRI Normal Superior AspectLCL MRI Insertion

 

2.  PCL

 

3.  Deep complex

 

A.  Popliteus tendon


Surgical Anatomy

- origin posterior tibia

- tendon passes through capsule and hiatus in coronary ligament of LM

- inserts on femur distal to LCL

 

Popliteus tendon intra-articular

 

Action

- acts to unlock the knee (ER femur or IR tibia) when flexing from terminal extension

 

MRI Anatomy

- need multiple images to watch coming around

- follow from muscle into tendon

- inserts in sulcus inferior to LCL

 

Popliteus MRIPopliteus Insertion

 

B.  Popliteofibular ligament

 

Surgical anatomy

- posterior fibular head to popliteus tendon

- 90% of people

- quite consistent

 

Action

- acts as check rein to popliteus

- important resistance to varus rotation and posterior translation

 

MRI Anatomy

 

Popliteofibular ligament MRIPopliteofibular MRI

 

C.  Posterolateral capsule

 

+ fabellofibular ligament

+ arcuate ligament

 

These are much more variable

 

LaPrade & Engebretsen Am J Sports Med 2003

 

Anatomy of the posterolateral corner

 

LCL

- insertion is 1.4 mm proximal to epicondyle and 3 mm posterior

- origin is 8 mm posterior to anterior fibular and 25 mm distal to fibula styloid

 

Popliteus

- inserts anterior aspect of popliteal sulcus

- femoral insertion always anterior to LCL

- average 18 mm from LCL insertion on femur

 

Popliteofibular

- anterior and posterior divisions from the popliteus to the posterior fibular

- posterior main division attaches to fibular styloid

 

Layers Lateral Knee (Seebacher)

 

1.  Superficial

- deep fascia of thigh

- ITB, biceps femoris tendon, CPN

 

2.  Middle

- patella retinaculum

 

3.  Deep

- posterolateral capsule with its thickenings

- LCL / Popliteus / Popliteofibular ligament

 

Actions

 

LCL

- 1° lateral stabiliser at 30° flexion

 

2° lateral stabilisers 

 

Dynamic

- ITB

- popliteus

- biceps femoris

 

Static

- popliteal-fibular ligament

- arcuate Ligament

- ACL

 

Tertiary medial stabiliser

- PCL

  

Incidence

 

5% of knee injuries have a component of PLC instability

 

Mechanism

 

Twisting injury 

 

Direct blow to anteromedial side of knee

- often hyperextension injury

 

Associated Injuries

 

PCL

ACL

CPN (10%)

 

History

 

Feeling of ripping

Swelling usually delayed (extra-articular)

 

Often instability with extension

- knee may buckle into hyperextension with weight bearing

- may walk with knee in flexion to maintain stability

 

Instability up and down stairs

 

Patellofemoral symptoms 

- secondary to posterior displacement of tibia

 

Examination

 

Gait / Stance

 

Varus thrust in gait and single leg stance

- due to ER of tibia 

- apparent varus

- flexed attitude to knee

 

LCL

 

Tested in extension & in 30° flexion

- somewhat theoretical because practically impossible to tear LCL in isolation

- usually associated posterolateral corner injury

- isolated LCL uncommon

 

Grade 1

- < 5mm laxity in 30o flexion

- indicates mild sprain of LCL

- up to 1/3 torn

- usually no laxity in extension

 

Grade 2

- 5-10 mm laxity in flexion

- indicates moderate sprain of LCL

- 1/3 to 2/3 torn

- usually no laxity in extension

 

Grade 3

- >10 mm laxity in flexion

- laxity in extension

- indicates complete disruption of LCL

- indicates disruption 2° restraints

 

LCL Instability ValgusLCL Instability Varus

 

PCL 

 

Laxity demonstrated by positive Lachmann

- posterior sag / loss of step off

- posterior drawer

- quadriceps active

 

 

Posterolateral Corner instability  

 

Posterolateral draw

- foot in ER

- apply a posterolateral rotatary force

 

External rotation recurvatum test

- pick up leg via great toe bilaterally

- tibia hyperextends

- tibia externally rotates due to loss of PLC

 

Dial Test 

- increased ER of Tibia >10° other side

- increased at 30o - PLC

- increased at 30o and 90o - PCL + PLC

 

Dial Test Positive at 30 degrees

 

Reverse Pivot Shift (Jacob et al)

- 35% patients positive / check normal knee

- valgus force, foot ER 

- flexion to extension

- reduction of posteriorly subluxed LTC

 

X-ray

 

Often normal

 

Bony avulsion of Fibula Head / Gerdy's tubercle

- LCL / biceps / ITB avulsion

 

LCL Avulsion Fibular HeadLCL Bony Avulsion

 

Lateral joint widening and subluxation

 

Knee PLC Xray Lateral Widening

 

PCL bony avulsion

 

MRI 

 

Anteromedial bone bruise

 

1.  LCL

 

Options

 

A.  Fibular avulsion / potential for direct repair

 

MRI Avulsion Posterolateral Corner Fibula

 

B.  Midsubstance / require reconstruction

 

Knee LCL Midsubstance Tear PLC injury

 

C.  Femoral avulsion / potential for direct repair

 

LCL Femoral Avulsion MRI

 

2.  Popliteus

 

Options

 

A.  Femoral avulsion / potential for direct repair

 

Popliteus Avulsion MRI

 

B.  Midsubstance / require reconstruction

 

Popliteus Musculotendinous Sprain

 

3.  Biceps Femoris

 

Usually avulsed from fibular head

 

MRI LCL and Biceps Fibular Avulsion

 

4.  PCL

 

Options

 

A.  Femoral avulsion / potential for direct repair

 

MRI PCL Femoral Avulsion

 

B.  Tibial avulsion / potential for direct repair

 

C.  Midsubstance / require reconstruction

 

MRI PCL midsubstance

 

5.  Posterior capsule

 

See oedema at posterior tibia on axial MRI

 

6.  ACL / MCL

 

Knee dislocation