If you asked the average person to pinpoint their posterolateral corner, it’s fair to say you’d probably get a blank look in return.
Few people have even heard of this rather overlooked body part, let alone realised they have two – one in each knee. But injuries to the posterolateral corner aren’t quite so rare as the obscurity suggests, particularly for anyone involved in contact sports or athletics, for example. Here’s how they work.
What and where is the posterolateral corner?
The posterolateral corner (PLC) is a collection of ligaments and tendons at the back and outside (i.e. “posterior and lateral”) of the knee. This includes things like your hamstring, popliteal muscle and popliteal tendon, among many others. It’s a complicated “junction box” of different tissues.
What does it do?
The PLC’s main task is stability. It protects your knee from external forces, for instance from becoming overextended when you turn quickly on the squash court. It also helps the locking and unlocking function that happens when you extend, rotate or bend your knee joint.
How do people damage it?
Usually in an accident – a nasty fall, a motorbike crash, or in sport. Typically, you’d suffer a powerful direct blow to the front-middle of your knee, causing it to rotate inwardly (this is known as a varus rotation). But they can also occur after hyperextension (over-straightening the leg) or when the knee bows suddenly.
Does anything else get damaged?
Yes. Very often. Most PLC injuries happen alongside other associated damage. Two common examples are an ACL injury (see our recent article, “What is an ACL tear?”) or a PCL tear, where one of the main ligaments in the knee joint gets overstretched or ripped. Another is a meniscal tear.
What problems does a PLC injury cause?
It depends on the severity of the injury – we usually grade them on a scale of I (mild) to 3 (severe) – but a key problem is loss of stability, so that your knee gives way or keeps buckling. Another potential issue is damage to the common peroneal nerve, which runs through this part of the knee. This can cause numbness down the leg and over the top of the foot, and possibly a weak inflexion.
How do you diagnose these injuries?
Because they often come with other injuries, PLC damage is easy to miss. First, we would give you a careful examination. We’ll want to know where you’re experiencing pain, when you get your instability, and whether your knee is over-rotating externally. We will also ask you to have an MRI scan, which allows us to see tissue damage that isn’t possible with an x-ray. It also helps us to identify damage to other tendons and ligaments. Diagnosing a PLC injury is important, because ongoing instability can cause arthritic damage – often quite rapidly (for more on arthritis, see this article: “The 60-second guide to Osteoarthritis”).
How do you treat posterolateral corner injuries?
Again, this depends on how seriously you’ve injured it – and what other damage you may be suffering in your knee (such as a torn meniscus). For mild PLC injuries, conservative treatments can work well. That could mean giving you a splint and a hinged knee brace to wear for a few weeks. We’d also refer you for physiotherapy to help improve your recovery.
What are the surgical options?
If you have a grade 3 injury, we will probably need to refer you for an operation. There are really two main options here:
Repair – this involves reconnecting the torn tendons or ligaments and reattaching them to the bone
Reconstruction – this means taking a graft from another tendon and using it to rebuild the damaged PLC tissues – often the popliteal tendon or the lateral collateral ligament (LCL)
Severe PLC damage is a significant injury that can hamper the careers of sportsmen and women. Reconstructions come with certain limitations, which may mean it’s difficult or impossible to return to previous levels of competition, or even to the sport itself. In general terms, however, these operations can do a lot to restore stability and protect the knee from further damage.
Interested in reading on? You might find these articles helpful
Joint 101: a beginner’s guide to the knee
The 60-second guide to Knee Braces
Ask the Physio: How can I avoid aches and pains in my desk job? And 8 other key questions answered
Have you recently injured your knee, or suffered other damage or instability? We can help you find out what’s going on. Drop us a line, or book an appointment directly on the website, and we’ll help you get the right diagnosis and treatment plan for your knee.