Postero lateral corner injury of the knee (PLC)

The posterolateral corner of the knee (PLC) is a very complex region both anatomically and functionally. In fact, the PLC of the knee plays a vital role in both static and dynamic stability to prevent excessive hyperextension, tibial external rotation, and varus angulation 

There is 16% of knee ligament injuries to the PLC of the knee. It is often overlooked during the clinical reasoning process. According to Pacheco, Ayre, et al 2011), a retrospective study showed that in 68 patients with PLC injuries. They had found 72% were not correctly diagnosed at the initial presentation. There were 12 months of delay diagnosis. This is due to a general lack of understanding of the role of the PLC. of course it’s awareness of accurate assessment procedures. 

Image courtesy of  Google Images,  retrieved March 8th, 2016
Image courtesy of Google Images,

Posterolateral corner(PLC) anatomy & biomechanics

The PLC is an important structure to provide stability of the knee joint at angles < 45° knee flexion during weight-bearing activities.

The three most important stabilizing structures of the PLC are the popliteus tendon, popliteofibular ligament and fibular collateral ligament are the most important stabilizing structures of PLC. (LaPrade & Wentorf, 2002; Lunden et al., 2010).

  1. The popliteus tendon acts as static as well as a dynamic stabilizer against the external rotation of the knee.
  2. The popliteofibular ligament assists with resisting varus stress. It is considered the primary restraint for knee external rotation forces. It is a crucial stabilizer to the PLC. It is typically surgically reconstructed when torn.
  3. the fibular collateral ligament is the primary static stabilizer to varus opening from 0-30*.
Image courtesy of  Google Images , retrieved March 8th, 2016. 
Image courtesy of Google Images, F.Gillard

The posterolateral joint capsule, coronary ligament, oblique popliteal ligament,and fabellofibular ligament provide additional static stability of the PLC. Many of the static stabilizing ligaments are in fact a thickening of the capsule.

In addition, primary static stabilizers, as well as other dynamic stabilisers, are required for the normal functioning of the knee. The popliteus complex contributes static as well as dynamic PLC stability. The lateral gastrocnemius tendon blends with the posterior capsule and popliteofibular ligament. The iliotibial band provides lateral knee stability. It acts in conjunction with the lateral capsule and ligaments which prevents varus positions of knee extension. The knee flexion and lateral rotation are done by biceps femoris short and long head. It resists varus angulation and works synergistically with the rest of the hamstring complex. This is to prevent excessive anterior translation of the tibiofemoral joint.

Patient history & clinical presentation

PLC mechanism of injury(MOI) involving a fall, sports trauma, or motor vehicle accident. Another strong MOI is knee hyperextension injuries. It is specially combined with Hyperextension + varus force to the knee. Type of injuries may be contact or non-contact. It can also originate from the valgus force applied during knee flexion + severe tibial external rotation during knee flexion or extension. 

Acute PLC presentation : 

  • swelling, pain 
  • occasional numbness and weakness in the foot as a result of peroneal nerve disruption. 
  • Peroneal nerve injury can occur in up to 13% of injuries.

The numbness will be along with the first dorsal web space and dorsum of the foot. Weakness in ankle dorsiflexion and eversion and great toe extension 

Patients may feel a sensation of instability or giving way during weight-bearing in extension during walking or on stairs in severe injury mechanism  

Patient examination

Let’s have a look at some of the aspects of physical examination to the diagnosis a PLC injury. 

1. Observation

  • Acute injury, there will often have heat and swelling of the joint. 
  • Gait analysis should be routinely assessed which will often have an antalgic gait. 
  • Careful attention in the stance phase helps us to determine varus thrust with or without hyperextension. It may be caused by a disruption to the lateral compartment structures resulting in an opening of this region. 
  • Patients usually obtain with a flexed knee to avoid stressing the joint and capsule in extension

2. Palpation

Accurate palpation assists in the differential diagnosis. Acute PLC injuries will usually be tender to palpation over the PLC of the knee joint and localized pain at the fibular head.

3. Special tests

Here are some tests considered by experts to be the most reliable for diagnosing injuries to the PLC injury.


In acute presenting case imagine can assist in identifying specific anatomical injured structures.where the physical examination may be limited due to pain and swelling. MRI is the preferred modality however it is dependent on the operator. Many authors reported that it is possible to identify the majority of individual structures in the PLC of the knee. Instability reveals complete tears of two or more structures of the PLC. Imaging can help the clinician in making an additional diagnosis in PLC injury. MRI is useful in chronic injuries when conservative treatment fails. 


Grading scales for PLC injuries of the knee (Lunden et al., 2010). 
Grading scales for PLC injuries of the knee (Lunden et al., 2010). 


It can be difficult in deciding which patients should have surgical construction in PLC injuries. Unfortunately, there is a lack of conclusive evidence. 

A conservative approach can be effective in less serious injuries. The recommended treatment for grade 1 to 2 PLC injuries is to immobilize the knee in extension for 3-4 weeks. Patients will walk non-weight-bearing. Rehabilitation is advised after the immobilization period to restore range of motion, increase weight-bearing and functional strength of the knee Currently, there are no randomized controlled trials comparing conservative treatment protocols. 

According to LaPrade, the treatment of PLC injuries has proved challenging. Reconstructive procedures used were neither anatomically based or biomechanically validated in past years. This has resulted in recurrent laxity and failures of a ligament. The development of new anatomically based reconstructive techniques has improved the outcomes of surgery and posterolateral knee stability . 

The first 12 weeks of injury, grade 3 PLC injuries should be managed. Acute repair within two weeks of injury is considered to be superior to reconstruction at a later stage, but due to the high frequency of missed diagnosis. If we manage timely and appropriately PLC injuries, outcomes are excellent.

there are no randomized controlled trials suggesting that this results in best outcomes, where the surgical literature advocating surgery for treatment of isolated grade 3 injuries. There is no high-quality evidence supporting acute repair is claimed to be more successful than delayed reconstruction. Additionally, the literature does report good outcomes of acute repair in case series and case reports.  PLC injuries are very commonly associated with the ACL, PCL, or both ligaments.It is current practice to repair both areas due to the possibility of cruciate graft rupture. 


In summary, the aspects of clinical examination can help improve the accuracy of diagnosis. During the initial stages of examination, emphasis should be on careful questioning of the mechanism of injury and symptoms. It helps to direct the assessment of posterolateral knee pain. Currently, the literature is difficult to assess due to the lack of standardization. Protocols for advanced conservative management have yet to be developed.

We are all driven and passionate to learn about different facets of our profession and through sharing of information, our knowledge base grows. 


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