The posterolateral corner is a complex system of 28 static and dynamic ligaments, tendons and nerves within the knee. The most important of these structures are the lateral collateral ligament, the popliteofibular ligament, the popliteus tendon, the posterolateral capsule, and the popliteofemoral ligament.

These structures help stabilize the knee joint and prevent excess rotation during movement. They also play a vital role in ensuring proper biomechanics of the knee.

Most posterolateral corner injuries occur in combination with injuries to the posterior cruciate ligament and the anterior cruciate ligament. In fact, over 70% of PLC injuries occur alongside damage to other structures in the knee¹.

Historically, the posterolateral corner was a poorly understood area of the knee, and diagnosis and treatment of injuries posed complex challenges. Fortunately, as research on knee injuries has become more sophisticated, there are now reliable options for addressing knee injuries in the posterolateral corner.

PLC injuries that are not treated can cause ongoing pain, knee instability and changes in the biomechanics of the knee. For this reason, it’s important to visit an orthopaedic specialist or sports medicine physician for any ongoing pain or knee instability.

What Causes a Posterolateral Corner (PLC) Injury?

The most common methods for injuring the PLC in the knee include:

– Sports – Hyperextension during football, basketball, lacrosse and soccer is a common source of injuries to the PLC. Direct hits to the proximal tibia can also cause injury.

– Car Accidents – High-energy direct impact to the knee, such as the knees hit a dashboard during a car accident, can cause damage to the structures in the PLC

– Falls – High-energy impacts to the anterior knee while the knee is flexed, like blows sustained during a fall, can cause damage to the structures of the PLC

Contact and noncontact hyperextension of the knee is associated with damage to structures of the PLC and other structures in the knee.

What Are the Symptoms of a Posterolateral Corner (PLC) Injury?

Injuries to the posterolateral corner are associated with widespread pain, tenderness and swelling in the fibular head and posterolateral area of the knee. These injuries can also cause knee instability, a change in gait, and hyperextension and varus thrust during during walking.

Varus thrust describes the bowing-out of the knee² while walking or when the knee is bearing weight. Hyperextension refers to the knee bending too far backward.

Individuals with a PLC injury may also report a feeling of the knee buckling or giving out during movement. This sensation may worsen when climbing stairs or walking up or downhill.

Another common symptom of damage to the posterolateral corner is a change in sensation or ability in the legs and feet. The peroneal nerve is commonly displaced³ when the PLC of the knee is injured. This can cause numbness, tingling, and pain in the legs, ankles and feet. It can also cause a sensation known as foot drop, or the inability to lift the front of the foot.

How Are Posterolateral Corner Injuries Diagnosed?

A thorough medical history and a number of physical exams are vital to properly diagnosing a PLC injury.

These physical tests include varus stress testing, the dial test, the external rotation recurvatum test and the reverse pivot shift test. All of these tests should be performed using the uninjured knee as a comparison⁴.

Orthopaedic doctors evaluate abnormalities in stability, movement, rotation and appearance of the knee and attached structures during these tests.

Radiography (x-rays) and MRI are also recommended to achieve an objective diagnosis of injury to the PLC and related ligament injury.

Untreated PLC injuries not only cause pain and instability in the knee joint, they can also compromise previous reconstructive knee surgery. Additionally, untreated PLC injuries can alter the biomechanics of the knee, leading to early-onset osteoarthritis and other degenerative changes.

How Are Posterolateral Corner Injuries Treated?

For patients with Grade I or Grade II PLC injuries, treatment typically consists of 3 to 4 weeks of full knee immobilization with the knee in full extension. After this period of immobilization, patients are gradually allowed to increase weight-bearing activity but typically need to move around on crutches for up to 10 weeks after the injury.

It is important for patients with PLC injuries to carefully evaluate their pain levels, instability in the knee joint, or issues with gait following treatment. Additional testing may be needed, and surgical repair of the knee may be required.

For patients with Grade III injuries to the PLC, surgical treatment is recommended. The success rates of these surgeries are far greater for acute injuries compared to chronic injuries. As a result, it is vital for patients to visit a medical specialist within 2 weeks of an initial injury to the knee.

The preferred surgical technique for these injuries is anatomical reconstruction of the three static stabilizing structures of the PLC. These structures are the fibular collateral ligament, the popliteus tendon and popliteofibular tendon.

Following surgery, patients will need to use a knee immobilizer and perform no weight-bearing activities for six weeks.

Patients with successful outcomes usually require 6 to 9 months to return to normal activities and sports following reconstructive surgery for the PLC.

PLC Injury Diagnosis and Treatment at Mobility Bone & Joint Institute

Mobility Bone & Joint Institute is the only practice in the Merrimack Valley that can diagnose diseases, infuse medications, and perform x-rays on site.

Do you have questions about the diagnosis and treatment of PLC injuries at Mobility Bone & Joint Institute?

Call (978) 794-1946 or click here to schedule an appointment at our Andover, MA office.

Call (603) 898-2220 or click here to schedule an appointment at our Salem, NH office.

1. “Posterolateral Corner of the Knee: Current … – NCBI – NIH.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4852053/
2. “Varus thrust and knee frontal plane dynamic motion in ….” https://www.sciencedirect.com/science/article/pii/S1063458413009102
3. “Displacement of the common peroneal nerve in … – PubMed.” https://pubmed.ncbi.nlm.nih.gov/16129747/
4. “Posterolateral Corner of the Knee: Current … – NCBI – NIH.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4852053/