What Is a Posterolateral Corner Injury?

Knee pain and swelling can be caused by a number of conditions or injuries. Among athletes, injury to the posterolateral corner (PLC) of the knee is one common cause of this type of pain.

The PLC is a group of anatomical structures that helps to support and stabilize the outside (lateral) region in the back of your knee. The primary role of the PLC is to prevent the knee from excessive amounts of rotation or bowing (turning) outward (also known as varus).

This article will discuss how the PLC can be injured, symptoms, the diagnostic process, and what the treatment options are if this type of injury occurs.

What Is the Posterolateral Corner (PLC)?

The posterolateral corner (PLC) is made up of multiple different muscle tendons, ligaments, and joint tissues that work to support and stabilize the outside of the knee.

These structures are commonly subdivided into primary and secondary stabilizers. The primary group includes:

• Lateral collateral ligament (LCL)
• Popliteofibular ligament (PFL)
• Popliteus tendon

In addition, a group of secondary stabilizers also help secure this area of the knee. This grouping includes:

• The lateral capsule of the knee
• Coronary ligament
• Lateral gastrocneumius tendon
• Fabellofibular ligament
• The long head of the biceps femoris
• Iliotibial (IT) band

The primary role of the PLC is to prevent the knee from turning outward too much. In addition, the grouping provides secondary assistance in preventing the lower leg bone (tibia) from shifting forward or backward on the thighbone (femur).

Occasionally, one or many of the PLC structures can be sprained, strained, or torn. Depending on the severity of the damage, this can cause high amounts of pain and may significantly affect your daily function.

How a PLC Injury Occurs

Athletic injuries are responsible for a sizable portion of PLC issues. Typically, an injury occurs when there is a direct blow to the inner portion of the front of the knee that causes the leg to bow outward.

A PLC injury may also be sustained without contact—for instance, if the knee hyperextends or buckles away from the other leg into a varus position. Because of the way your knee usually moves during a posterolateral corner injury, concurrent sprains or tears to the anterior cruciate ligament (ACL) or posterior cruciate ligament (PCL) are also very common.

PLC injuries can also be caused by several other situations. In particular, motor vehicle crashes and falls from elevated surfaces are frequently at fault. It is also worth noting that when this type of trauma causes a PLC injury, bony fractures to the leg are also common.   

Symptoms of a PLC Injury

Depending on the severity of your PLC injury, multiple different symptoms may be present. These include:

• Significant pain, swelling, bruising, and hardening in the knee and surrounding areas
• Outward bowing position of the affected knee in standing
• Difficulty walking or negotiating stairs due to feelings of instability
• Numbness or tingling in the lower leg
• Foot drop on the injured side

If you suspect that you have sustained a PLC injury or have any of the symptoms listed above, it is critical to be seen by an orthopedic specialist or emergency room physician. Your healthcare provider will be able to properly evaluate your leg and ensure that the appropriate treatment is initiated.

How a PLC Injury Is Diagnosed

Diagnosing a PLC injury begins with a comprehensive examination. In addition to looking for the symptoms noted above, your healthcare provider will typically move your legs in several different directions to assess for any instability. They may also perform the dial test, which involves having you lie on your stomach while a healthcare professional assesses the side-to-side rotation in your leg to check for excessive motion.

In addition, imaging is frequently ordered to more accurately look at which anatomical structures are affected.

X-rays can be helpful in ruling out any concurrent fractures and in checking for excessive laxity in this area of the knee.

Magnetic resonance imaging (MRI) is also useful for visualizing the various tendons and ligaments in the PLC. This type of image helps your healthcare provider take a closer look at any sprains or tears that have occurred. MRIs may be less accurate in diagnosing PLC issues after 12 weeks have elapsed, however, so they should be obtained as soon as possible if needed.

Based on this evaluation, your injury may be classified using the following system:

• Grade 1: 0 to 5 degrees of rotational or varus instability and an intact PCL
• Grade 2: 6 to 10 degrees of rotational or varus instability and an intact PCL
• Grade 3: 11 or more degrees of rotational or varus instability and a ruptured PCL
  

Treatment Options for PLC Injuries

The care you receive after a posterolateral corner injury can vary significantly depending on the structures involved and the overall severity. The sections below offer more details about the conservative and surgical treatment options that are available.

Nonoperative Treatment

Nonsurgical treatment is typically reserved for isolated grade 1 or grade 2 PLC injuries.

Depending on which structures are affected, a stabilizing brace may be worn and crutches are often needed to temporarily decrease the strain on the knee.

Physical therapy (PT) is also commonly prescribed. Your physical therapist will focus on the following goals:

• Weaning you from your crutches and improving your walking pattern
• Regaining the range of motion in your knee
• Building strength and power in your leg muscles
• Improving balance and stability in the affected lower extremity
• Reintroducing sport-specific movements like running, cutting, and jumping when appropriate

Operative Treatment

People with grade 3 PLC injuries often respond poorly to nonoperative treatment. They may also suffer from chronic knee instability or long-term osteoarthritis development if surgery is not performed. Because of this, operative treatment is typically recommended for injuries of this magnitude.

Typically, any primary stabilizers in the PLC that were damaged are surgically reconstructed using a graft (tissue) from another region of the body. In some cases, a graft from a cadaver may also be utilized.

Surgical repairs may also be performed on any of the secondary stabilizers in the PLC to improve stability. Any other ligament injuries (such as to the ACL or PCL) or concurrent fractures may also need to be addressed.

Following the procedure, you are frequently required to immobilize your knee with a brace and to stay non-weight bearing on the affected leg to protect the surgical area. This can last for six weeks or more depending on your surgeon’s recommendations.

Physical therapy is also commonly initiated after your procedure. The goals of PT are often the same as when treating milder PLC injuries, though rehab typically progresses at a slower pace. It may take six months of PT or more to return to sports or exercise after this type of surgery.

Summary

The posterolateral corner (PLC) is made up of muscles, tendons, and ligaments in the back of the knee. An injury to the structures in this region—usually sustained during contact sports or trauma such as a car accident—can cause significant pain and impair mobility. Treatment options will depend on the severity of the injury but may include physical therapy to heal and strengthen the PLC or reconstructive surgery.

A Word From Verywell

Posterolateral corner injuries can cause significant pain and may dramatically impact your ability to walk, work, or maintain your independence. Because of this, it can be a frustrating and scary issue to cope with.

To ensure you are able to return to your normal activities as quickly as possible, it is crucial to have your injury evaluated by a healthcare provider soon after an injury occurs or you notice knee pain or other symptoms. Your healthcare provider can provide a diagnosis and outline the treatment options that are available. Take heart in knowing that while rehab can take time, a full recovery is possible.