Posterolateral Corner

The posterolateral corner (PLC) of the knee has a complex, and often misunderstood, anatomy that serves the purpose of stabilizing the knee.³

Posterolateral Corner: Anatomy

The posterolateral corner (PLC) of the knee is comprised of the following:²

Primary stabilizers

Lateral (Fibular) collatoral ligament (LCL):⁴

Originates from the small osseous depression approximately 1.4mm proximal and 3.1mm posterior to the lateral femoral epicondyle and immediately anterior to the femoral attachment of lateral head of gastrocnemius tendon
Extends distally to insert on lateral aspect of fibular head, anterior and distal to fibular styloid process, and merges with distal biceps femoris tendon

Popliteus Musculotendinous Complex (i.e. popliteus muscle, popliteus tendon, PFL):

Popliteofibular ligament (PFL):⁴

Originates from popliteus tendon proximal to myotendinous junction
Inserts onto anterior of medial aspect of fibular styloid process

Popliteus tendon (consists of anterior and posterior bundle)⁴

Originates from popliteus muscle and extends into the popliteal hiatus, coursing under and anterior to LCL
Inserts onto anterior fifth portion of popliteus sulcus of lateral femoral condyle

Secondary contributors

Coronary ligament of the lateral meniscus

Originates medially, lateral to the posterior cruciate ligament (PCL) with its lateral border at the edge of the popliteal hiatus

Fabellofibular ligament

Originates on lateral aspect of fabella⁴
Attaches lateral to tip of fibular styloid⁴
Is inversely proportional in size to the vertical or lateral limb of the arcuate

Iliotibial band (IT Band)

Superficial layer covers lateral aspect of knee with distal attachment at Gerdy’s tubercle
ITB has posterior fiber attachments to the lateral tibia where it meets oblique fibers from the LCL

Lateral gastrocnemius tendon

Originates at the lateral edge of the lateral gastrocnemius muscle, extends proximally to a bony fabella, and attaches to the femur in the region of the lateral supracondylar process

Biceps femoris tendon

Long head: Originates from ischial tuberosity, and inserts anterior and posterolateral aspects of fibular head4. Its fibular head insertion laterally next to the FCL is sometimes referred to as the misnomer “conjoined” tendon.
Short head: Originates off of the lateral prolongation of the linea aspera of the femur, and inserts onto anteromedial aspect of fibular head⁴

Mid-Third Lateral Capsular Ligament

Originates on the femur just anterior and proximal to the lateral epicondyle posteriorly to the supracondylar process of the lateral femoral condyle, extends to the meniscus, then further to attach to the tibia posterior to Gerdy’s tubercle at its anterior aspect, and ends at the anterior edge of the popliteal hiatus.

Posterolateral Corner: Injury

Posterolateral corner injury of the knee can result in long term joint instability and cruciate graft failure if these are not identified and treated.¹ Mechanisms include varus twist and knee dislocations. When combined with posterior cruciate injuries, the patient may experience posterolateral rotatory instability (PLRI), which, if missed, may be recurrent. With external tibial rotation, the lateral tibia lurches backward and the knee opens laterally in a varus posture.

Most common cause is posterolaterally directed blow to anteromedial aspect of proximal tibia while knee is in full extension.⁴

Posterolateral Corner: Clinical Presentation

Damage to the anteromedial tibia while in extension commonly results in PLC injury by producing varus stress.⁵

Posterolateral Corner: Pearl

Serious PLC corner injuries must prompt a careful analysis of the peroneal nerve.

Posterolateral Corner: Treatment

Treatment is based on injury classification based on the degree of varus instability. Grades I (mild sprain) and II (partial tearing) injuries could be treated via conservative methods such as immobilisation of the knee, while Grade III (complete rupture) injuries may require operative procedures.⁴

Posterolateral Corner: Example

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HISTORY:

28-year-old male. Right knee pain and swelling; was playing football last Sunday and while making a cut felt something in his right knee. No prior surgery.

Image 1 - Ds2 WSE 2D Oblique Image 2 - Ds2 WSE 2D Oblique

Image 3 - Axial FSE 2D

Image 1 - Inferolateral meniscal fascicle tear

Image 2 - Popliteofibular ligament tear

Image 3 - Partial thickness popliteus tendon tear

FINDINGS:

Lateral retinaculum, MPFL and patellar alignment are normal. No high-grade chondromalacia of the patellar or trochlear cartilage.

Quadriceps tendon, patellar tendon and flexor mechanism are unremarkable.

Complete midbody tear of the ACL with anterior tibial translation. PCL is intact. Grade 3a MCL sprain. Posterolateral corner injury, with tear of the popliteal fibular ligament, posterolateral and posteromedial meniscocapsular rupture with hemorrhage, lateral meniscopopliteal complex tear, and partial tear of the popliteus tendon at the origin. Oblique tear of the posterior body of the medial meniscus measuring 2-2.5cm in length. Oblique tear of the posterior corner of the lateral meniscus measuring 2.5cm in length.

3-4+ hemarthrosis. Chondral body at the base of the PCL measuring 6 x 5 x 8mm, best seen on series 80801, image 12.

Subchondral depressed impaction fracture of the lateral femoral condyle at the terminal sulcus with reactive osteoedema. Displaced chip fracture of the posterolateral tibial plateau with active osteoedema. No high-grade chondromalacia of the medial or lateral compartments.

Musculature and marrow signal are normal. No posterior soft tissue masses or Baker's cyst. The neurovascular bundle is intact.

CONCLUSION:

Violent Pivot shift injury with complete midbody tear of the ACL, massive posterolateral corner injury, meniscocapsular rupture with hemorrhage postero- medial andpostero- lateral, and 3-4+ hemarthrosis. Associated depressed subchondral impaction fracture of the lateral femoral condyle and displaced chip fracture of the posterior lateral tibial plateau.

Oblique posterolateral corner ligament lateral meniscus tear measuring 2.5cm in length.

Oblique 2-2.5cm tear of the posterior body of the medial meniscus.

Chondral body at the base of the PCL.

Posterolateral Corner: Appendix

SUMMARY OF POSTEROLATERAL CORNER³

Posterior Cruciate Ligament (PCL)

1° restraint to posterior translation [greatest at 90° flexion]
2° restraint to extension rotation [greatest at 90° flexion]

Posterolateral Capsule

1° restraint to extension rotation [greatest towards extension]
2° restraint to posterior translation [greatest towards extension]

Lateral Collateral Ligament (LCL)

1° restraint to varus
Contributes little to extension rotation [popliteus and arcuate most important]

Posterolateral Corner: References

Knipe H, Rezaee A, et-al. Posterolateral corner injury of the knee: Radiopaedia (sourced 10Jan2018): https://radiopaedia.org/articles/posterolateral-corner-injury-of-the-knee
Moorman, CT. and LaPrade, RF., The Journal of Knee Surgery, Anatomy and Biomechanics of the Posterolateral Corner of the Knee, Vol.18 (2), 2005.
Pomeranz SJ., Gamuts & Pearls in MRI & Orthopedics. Ohio, The Merten Company, 1997.
Rosas HG., RadioGraphics, Unraveling the Posterolateral Corner of the Knee, Vol 36: 1776-1791, 2016.
Vinson EN, Major NM and Helms CA, Musculoskeletal Imaging, The Posterolateral Corner of the Knee, Vol.190, 2008.