Posterolateral corner injuries of the knee

Careful evaluation is essential to determine how a posterolateral corner injury has occurred and which anatomical structures are damaged.

First published 2009 by Dr Frank R Noyes, and reviewed August 2023 by Dr Sheila Strover (Clinical Editor)

How do posterolateral corner injuries occur?

A blow (from an opponent or object) to the top and inside (anteromedial) part of the tibia during sports and motor vehicle accidents are common ways that the PLC is injured.

As well, a noncontact injury in which the knee hyperextends and the tibia twists outward may tear these tissues. High-energy trauma, such as that sustained in a motor vehicle accident, is another common cause of PLC injury.

An isolated complete PLC rupture is rare as usually the injury is accompanied by a tear to the ACL or PCL.

Assessing the integrity of the posterolateral corner

A comprehensive evaluation of the PLC, as well as all of the other major knee structures, must be performed to determine all of the injuries or deficient ligaments and soft tissues, as well as any abnormal alignment or bone problems. To exclude any of the tests described below may result in an improper diagnosis.

At my Center, we do the following:

First, we take a thorough history, carefully determining to the best of the patient’s ability how the injury occurred, if swelling was noted immediately, if walking was tolerated, and other factors.

Then we examine:

- knee flexion, extension

- joint effusion

- the patellofemoral joint

ie. how far the kneecap moves side-to-side, crepitus on movement, pain

- tibiofemoral crepitus, joint line pain, compression pain

- gait, or walking pattern (looking for severe hyperextension on walking)

Muscle strength

We perform all ligament tests:

[This article was published in Noyes’ Knee Disorders: Surgery, Rehabilitation, Clinical Outcomes, Noyes FR, Barber-Westin SD (eds.), Copyright Saunders, 2009 - Noyes FR, Barber-Westin SD: Primary, double, and triple varus knee syndromes: Diagnosis, osteotomy techniques, and clinical outcomes, pages 821-895.]

We order imaging:

MRI, bone scan: if required, done for multiple ligament injuries

X-rays

• Anteroposterior
• Lateral, 30° flexion
• Posteroanterior, weight bearing, 45° flexion
• Patellofemoral axial
• Lateral stress, neutral tibial rotation
• For PCL ruptures: posterior stress
• Varus malalignment (see Figure on right): Full standing radiographs, mechanical axis and weight bearing line

For dislocated knees, a lower extremity venous ultrasound is obtained in knees that have swelling and soft tissue damage. An initial delay before any surgery is considered for 5 to 7 days to allow for observation of the neurovascular status, soft tissue swelling, skin integrity, and some clearing of hemorrhage in soft tissues in the injured extremity.

Classification of partial to complete posterolateral corner injuries

It is important to understand that injuries to the PLC structures vary, with some patients sustaining only mild to moderate damage and others having severe ligament and soft tissue ruptures. The examination I just described allows the classification of these injuries into either a first, second, or third degree injury.

In a First Degree injury, there is:

• Minor tearing of the fibers of the ligament
• Minor tenderness and swelling
• Little to no increase in lateral joint opening and external tibial rotation

In a Second Degree injury, there is:

• Partial tearing to the ligament involving 1/3 to 2/3 of its fibers
• Tenderness and swelling to the lateral soft tissues
• Little to no increase in lateral joint opening and external tibial rotation

In a Third Degree injury, there is:

• Definite tear to the ligaments. This may involve either a complete FCL tear alone, a complete FCL tear and a partial tear to the PMTL and posterolateral capsule, or a complete tear to all of these structures.
• Tenderness and swelling to the lateral tissues
• Definite increases in lateral joint opening and external tibial rotation, the amount depends on how many posterolateral structures are damaged.

The treatment of these injuries depends on the degree of damage. First and second degree injuries do not require surgery, but are treatment with rehabilitation and bracing in some cases, as discussed in Part 4. The third degree injury patterns require much more extensive treatment, as I will discuss in Parts 4 and 5.