Posterolateral Corner Injury of Knee

The posterolateral corner  injury is commonly associated with anterior cruciarte or posterior cruciate ligament injuries.

Isolated injuries to posterolateral corner are rare.

The injury usually occurs by a blow to anteromedial knee, varus blow to flexed knee, hyperextension injuries and  knee dislocation.

Peroneal nerve injuries are commonly associated.

Once referred to as dark side of knee, posterolateral corner of knee is well understood part of knee anatomy and biomechanics.

A high level of suspicion is recommended based on the trauma setting and the patient symptoms. Failure to address this condition may place other reconstruction graft at risk and result in poor outcomes

Anatomy of Posterolateral Corner

Posterolateral corner is constituted by following structures

Static structures

• Lateral Collateral Ligament(most anterior structure inserting on the fibular head)
• popliteustendon
• popliteofibularligamen
• lateral capsule
• arcuate ligament
• fabellofibular ligament

Dynamic structures

• biceps femoris(inserts on the posterior aspect of the fibula posterior to LCL)
• popliteus muscle
• iliotibial tract
• lateral head of the gastrocnemius

These structures can be seen as primary and secondary stabilizers

Primary Stabilizers

Lateral Fibular Collateral Ligament

The fibular collateral ligament is the primary varus stabilizer of the knee. It attaches to femur in a in a small bony depression slightly proximal and posterior to the lateral epicondyle. It courses distally to insert on the fibular and peroneus longus fascia.

Popliteus Tendon

The femoral insertion of the popliteus is about 20mm anteriorly from the FCL attachment with the knee at 70°. It courses posterodistally in an oblique fashion to insert into the posteromedial tibia. It becomes tendinous in the lateral third of the popliteal fossa

Popliteofibular Ligament

The popliteofibular ligament originates at the musculotendinous junction of the popliteus. It has anterior and posterior divisions  that insert distally into the posteromedial aspect of the fibular head.

Secondary Stabilizers

These structures are:

• The lateral capsular thickening with its components consisting of the meniscofemoral and meniscotibial ligaments.
• The coronary ligament
  • Attaches the posterior aspect of the lateral meniscus to the tibia.
• Lateral gastrocnemius tendon
  • Attaches nearly 14 mm posterior to the femoral attachment of fibular collateral ligament.
  • Courses distally in intimate relationship with the posterolateral capsule to fuse with the medial gastrocnemius and the soleus.
  • Serves as an important landmark during surgical reconstruction.
• The fabellofibular ligament
  • Distal thickening of the capsular arm of the short head of the biceps femoris
  • Extends vertically from the fabella to the fibular styloid.
  • The fabella is a sesamoid bone found within the proximal lateral gastrocnemius tendon in 30% of individuals.
• The long head of the biceps femoris
  • It divides approximately 1 cm proximal to the fibular head into direct and anterior arms.
  • The direct arm inserts onto the posterolateral aspect of the fibular head
  • The anterior arm has a small insertion site on the more distal and anterior aspect of the fibular head.
  • Both arms enclose the fibular collateral ligament distal attachment
• The iliotibial band
  • A broad layer that attaches onto Gerdy’s tubercle in the anterolateral aspect of the tibia.
• Numerous peripheral attachments to the patella, the lateral intermuscular septum and the capsule exist

Layering of structures

Lateral Structures of Knee by Layer

Layer I

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

Biomechanics of Posterolateral Corner

The posterolateral corner structures provide the primary restraint to varus forces of the knee as well as posterolateral rotation of the tibia relative to the femur.

When a knee is cruciate deficient, these structures are also important secondary stabilizers to anterior and posterior tibial translation.

The fibular collateral ligament is the primary restraint to varus stress across the knee, the rest of the posterolateral structures act as secondary varus stabilizers.

Fibular collateral ligament  and the popliteus complex are the primary restraints for tibial external rotations, especially between 30° and 40° of flexion. Posterior cruciate ligament acts as secondary restraint. popliteus works synergistically with the posterior collateral ligament  to control varus, and posterior translation too.

Popliteus and popliteofibular ligament function maximally in knee flexion to resist external rotation

The popliteus tendon  is a minor primary stabilizer (the anterior cruciate and anteolateral ligament  being the main stabilizer)

Minimal contribution of the posterolateral corner has been reported for anteroposterior tibial translation specifically in full extension and with anterior or posterior cruciate deficient knees.

Lateral collateral ligament  is primary restraint to varus stress at 5° and 25° of knee flexion

Classification of Injury

Grade I (0-5mm of lateral opening and minimal ligament disruption)

Grade II (5-10mm of lateral opening and moderate ligament disruption)

Grade III (>10mm of lateral opening and severe ligament disruption and no endpoint)

Clinical Presentation of Posterolateral Corner Injury

There would be a history of a specific trauma that occurred to their knee. Direct blow to the anteromedial knee is the common mechanism of injury to posterolateral corner.

Hyperextension and non-contact varus stress injuries can also injure posterolateral corner.

Most often, PLC tears are associated with ACL and/or PCL injuries.

Pain is the most frequently reported symptom.. Instability in mediolateral direction is reported especially in extension and patient finds it difficult to walk on uneven surfaces and stairs. There would be difficulty with  pivoting and cutting.

Instability and difficulty walking can lead to  as a varus thrust gait during the initiation of the stance phase.

A parasthesia or numbness may indicate peroneal nerve injury.

On examination patient would walk with a varus thurst or hyperextension thrust. There would be varus laxity on giving varus stress.

Special Tests

All tests should be performed bilaterally to compare to the uninjured knee.

Varus Stress Test

It is performed both in full extension and at 20-30° of flexion.

For testing in full extension, the femur is stabilized to the examination table with one hand [Same hand also assesses the amount of lateral compartment opening]. The other hand holds foot or ankle of the limb. Lateral compartment gapping is noted. The test is repeated with contralateral limb nd the gapping compared.

The test is repeated with  the knee flexed to 30°.

An abnormal opening at 30 degrees of knee flexion indicates  an injury to the FCL and potentially to the secondary stabilizers of the posterolateral corner of knee. If stability is restored when tested in full extension, an isolated injury to the FCL is presumed. However, if the varus instability persists in full extension, a combined FCL, PLC and cruciate ligament injury is assumed.

Dial test

The dial test  measures external rotation of the tibia relative to the femur. It is done in prone or supine position with knee flexed to 30 degrees.

The femur is fixed with one hand while the ankle and foot are externally rotated. An increase of more than 10° of external rotation compared with the contralateral side suggests an injury to the posterolateral corner.

The knee is then flexed to 90°. Because of its role as an important secondary stabilizer, a knee with an intact PCL will see a decrease in external rotation. If, at 90°, there is an increase in external rotation, as compared with 30°, a combined PLC and PCL injury is presumed.

Reverse pivot shift test

The knee is  positioned at 90° and external rotation and valgus force applied to tibia. As the knee is extended the tibia reduces with a palpable clunk because tibia reduces from a posterior subluxed position at ~20° of flexion to a reduced position in full extension. This reduction is the result of the iliotibial bandfunction changing from knee flexor to knee extender with extension and indicates injury to posterolateral corner with a positive predictive value of 68%.

External rotation recurvatum

The patient is in the supine position with legs extended. The  great toe is grasped and the leg lifted from the table while securing the femur to the table by applying gentle pressure to the anterior distal femur. The height of the heel knee is then measured and compared with the contralateral side. A positive external rotation recurvatum test predicted a combined ACL and PLC injury though the test is not sensitive.

Posterolateral drawer test

This test is performed with the hip flexed 45 degrees, knee flexed 80 degrees, and foot is 15 degrees of external roatation.

A  combined posterior drawer and external rotation force is then applied to the knee to assess for an increase in posterolateral translation i.e. lateral tibia externally rotates relative to lateral femoral condyle.

Imaging

Radiographs

Standard anteroposterior, lateral and sunrise view radiographs of the knee should be obtained. In acute injuries, these x-rays are often normal.

For chronic posterolateral corner injuries, a standing long-leg AP alignment radiograph is a requirement because malalignment needs to be recognized and corrected with a biplanar osteotomy before the surgical reconstruction.

Stress Views

Varus stress radiographs at 20 degrees of knee flexion evaluates the severity of these lesions objectively. The radiograph is obtained for both limbs.

Lateral compartment gapping is determined by measuring the shortest distance between the subchondral bone surface of the most distal aspect of the lateral femoral condyle and the corresponding tibial plateau.

An isolated complete FCL tear has a side-to-side difference of 2.7 to 4.0 mm, while a difference of greater than 4 mm represents an associated grade III PLC injury.

MRI

MRI assists in the diagnosis of acute lesions, assesses concurrent injuries and determines the location of the damaged structures.

Treatment of Posterolateral Corner Injury

Non-operative  Treatment

This consists of immobilization of knee in full extension with  protected weightbearing for about two weeks.

This treatment is indicated in grade I or II injuries of posterololateral corner which are not associated with any other injury.

This immobilization is followed by progressive functional rehabilitation.

Grade  III PLC injuries show poor outcomes with non-operative treatment.

Operative Treatment

This treatment is indicated in isolated posterolateral corer injuries grade II or injuries associated with other concomitant injuries.

Following surgical options are available

PLC repair

This is indicated in isolated PLC injuries with bony or soft tissue avulsion and in patients which could be operated within 2 weeks of injury.

A free graft may be used for augumentation.

PLC reconstruction

It is used in most grade III isolated injuries. It is also indicated when the repair is not possible or the tissue quality is poor.

The goal is to reconstruct lateral collateral ligament and the popliteofibular ligament using a free tendon graft from semitendinosus or Achilles.

Improved outcomes are associated with early treatment

PLC repair/reconstruction,  ACL and/or PCL reconstruction with or without High Tibial Osteotomy

It is indicated in combined ligament injuries. High tibial osteotomy is indicated in patients with varus mechanical alignment. Achievement of bony alignment favors outcome of ACL and PLC reconstruction success

The limb is immobilized and  make protected weight bearing for 4 weeks, after which passive range of motion is begun.

Constructions have less revision rates than ligament repair.

References

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