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
- 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
- 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
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
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.
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]
- 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.