Posterolateral corner (PLC) of knee

Anatomy of PLC

3 major static stabilizers of PLC

  1. Lateral collateral ligament
  2. Popliteus tendon
  3. Popliteofibular ligament

Other static stabilizers of PLC

  1. Lateral capsule thickening
  2. Arcuate ligament
  3. Fabellofibular ligament

Dynamic stabilizers of PLC

  1. Biceps femoris
  2. Popliteus muscle
  3. Iliotibial band (ITB)
  4. Lateral head of gastrocnemius

There are 2 “Y” shaped structures in the posterolateral corner of the knee.

1. Popliteus tendon, Popliteofibular ligament and Popliteus forms a “Y” shaped structure.

2. Arcuate ligament forms another “Y” shaped structure. Its medial limb attaches to oblique popliteal ligament and lateral limb is invariable and less distinct.

posterolateral corner knee

Biomechanics of PLC

1. Varus restraint: Primary (LCL) and Secondary (Other structures of PLC)

2. Tibial external rotation restraint (esp. at 30-40° flexion): Primary (LCL and popliteus complex) and Secondary (PCL)

Signs and Tests for PLC injury

1. Gait: Varus thrust or Hyperextension varus thrust (apparent tibia vara due to external rotation of tibia on full extension) or walking with slight knee flexion (to avoid instability and stresses on joint and capsule that occurs in hyperextension)

2. Increased external rotation: Dial test

3. External rotation recurvatum test

4. Posterolateral drawer test

5. Reverse pivot shift test

Modified Hughston Classification

GradeI (Mild)II (Moderate)III (Severe)
Varus stress – lateral opening at 30 degrees knee flexion0-5 mm6-10 mm>10 mm
Dial test – rotational instability0-5 degrees6-10 degrees>10 degrees

What is triple varus alignment?

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