The posterior lateral corner of the knee is the back outside area of the knee. Injuries here can happen in sports or other accidents and most of these don’t need surgery. Let’s dig into this topic and also spend some time going over an injury where surgery was recommended, but not needed.
What Causes Posterior Lateral Knee Pain?
In order to understand posterior lateral corner injury, you have to know what’s in this area. So first let’s review the anatomy (1):
- The posterior-lateral meniscus
- The popliteus tendon
- Popliteofibular ligament
- Biceps femoris tendon
- Lateral collateral ligament
- Fibular head
- Peroneal nerve
- Lateral head of the gastroc muscle
The posterior-lateral meniscus is part of the figure-8 meniscus complex that acts as a shock absorber for the knee bones. In the posterior-lateral corner, the meniscus can be injured, however, be careful about the diagnosis of a meniscus tear if you’re older than 35, as these are common in patients without pain (2). Hence, if you have a meniscus tear seen on MRI and you’re older, it’s not likely that this is a cause of pain, but just the result of wear and tear. In addition, the most common meniscus surgery that removes the torn bit (partial meniscectomy) has been shown in three large clinical trials to be no better than sham surgery or physical therapy (3,4, 11, 12).
The popliteus tendon sits in a bony groove here with the muscle living in the back of the knee (red in the diagram shown here) (13). The tendon can be injured and this may be seen on MRI or ultrasound imaging. In addition, one of its jobs is to pull the meniscus out of the way when the knee extends, so a bum tendon can cause meniscus pain. Patients with pain here often have a “boot sign” which means they get pain on the side they use their foot to take off the opposite shoe or boot.
The popliteofibular ligament (orange in the diagram above) goes from the fibular head around the popliteus tendon and controls tibial rotation similar to the PCL ligament.
The biceps femoris tendon is the insertion of the outside hamstrings muscle at the fibula bone (14). The tendon can be injured and irritated low back nerves may cause abnormalities in muscle firing that can cause inflammation in this tendon. This pain is made worse by bending the knee.
The lateral collateral ligament (LCL) is the outside ligament of the knee that stabilizes it when pressure is placed from the inside to outside (varus pressure) (blue in the diagram above) (15). It can be injured and is often stretched more often than it is completely torn. Be a bit careful here, as even though many MRI reports may say that the LCL is “torn” it’s usually still intact with damaged fibers. Surgery is rarely needed here.
The fibular head is the small outside bone of the leg which attaches here to the bigger bone (tibia) and is held on with strong ligaments (tibiofibular) (green in the image above) (16). There is a joint here which can be damaged or become arthritic. Also, the ligaments can be damaged making the fibula unstable. Hence, most of the pain here is often from an arthritic joint.
The peroneal nerve wraps around the fibular head here and if this is unstable, the nerve can be irritated (17). When the nerve is aggravated, it can cause tingling, numbness, or burning down the front of the leg and foot. If the nerve is injured, tapping on the area will set the nerve off (Tinnel’s sign).
The lateral head of the gastroc muscle is where the outside of your calf muscle attaches to the top leg bone (femur) (yellow in the image above) (18). This tendon or muscle can be torn or injured. This pain would be made worse with dorsiflexion of the foot (stepping on the gas motion).
What Is Posterolateral Instability of the Knee?
First, what is instability? Your joints are held together by ligaments and sometimes muscles and tendons. When these are properly tight, they guide the joint and allow little motion that isn’t pre-planned. However, when they’re damaged, too much movement is allowed in the wrong directions and this is called instability.
The ligaments injured that can cause posterior-lateral instability are quite a few. First, the internal ligaments in the knee (ACL and PCL) control pivoting movements at the knee. When they are loose, this can cause too much force on this part of the knee (posterior-lateral corner) and irritation or damage to any of the structures listed above. In addition, the LCL, tibiofibular ligaments, and popliteus tendon can also be damaged and allow too much motion.
Does a Posterior Lateral Corner Injury Heal?
Many of these injuries will heal with time and rehab. Bracing for 4-6 weeks is usually the first treatment. PT will focus on strengthening the muscles that help to stabilize the rotation. That includes those at the spine, hip, outside hamstrings, and popliteus. Knee stability in landing may be emphasized once the knee is feeling better.
What is a Posterolateral Corner Reconstruction?
These surgeries are considered when physical therapy fails and the patient can’t return to sports without pain and swelling. Generally, this term is used to describe a bucket of different, but related surgeries. This can include reconstructive surgery of the PCL, LCL, popliteus tendon, fibular head ligaments (proximal tibiofibular joint reconstruction), and posterior-lateral corner capsular reconstruction (5).
The PCL reconstruction involves replacing the ligament with one or two tendons (19). The original ligament has two bands which help it stabilize rotation of the knee joint, especially the posterior lateral corner of the knee. Single tendon reconstruction is simpler but less efficient at stabilizing tibial rotation. A two tendon reconstruction is more technically difficult but comes closer to replacing the normal biomechanics of the damaged ligament.
Many of these surgeries can be performed together (20). For example, the image to the right shows a lateral collateral ligament reconstruction with a tendon graft (red) that’s anchored into the femur (outside of the thigh bone) and then anchored in a tunnel drilled in the fibula. The popliteus tendon and ligament are also reconstructed here with a tendon anchored in the front of the tibia and then threaded to the back and then up to the outside of the femur (blue). A tendon is then also threaded through the same tibial tunnel and anchored into the fibula to recreate the ligament that holds that bone to the tibia (orange).
Tibiofibular joint reconstruction is performed when the ligaments that hold the fibula to the tibia are damaged (6). Here the surgeon takes a tendon and anchors it to the femur and then drills a hole in the fibula. That tendon is then threaded through the fibula and/or back to the femur (left).
The posterior-lateral corner capsular reconstruction involves first an osteotomy (cutting of bone) of the outside end of the thigh bone (lateral femoral condyle) to improve visualization of the area. The joint capsule (the covering of the knee joint) is then sutured to tighten it down in an attempt to reduce instability (5).
What Are Surgical Outcomes Like?
Regrettably, patients that get multiple areas reconstructed don’t do as well as those who need a single ligament reconstructed like an ACL. For example, in one study, combined ACL surgery with a posterior-lateral corner reconstruction had poorer outcomes than an ACL surgery alone (8). In another study that looked at PCL surgery plus posterior-lateral corner, only 1/3 of patients had normal ligament testing after surgery with most having some laxity and about a quarter of the patients had no improvement (9). There are also no high-level studies showing that these procedures are more effective than sham or placebo surgeries (10).
What Are the Side Effects of Surgery?
Complications can include persistent laxity, bone death (osteonecrosis), nerve or blood vessel injury (neurovascular), compartment syndrome, scarring in the knee causing lost motion, pain in the front of the knee, fractures, infection, and wound healing problems (7).
Do You Need Surgery or Can Newer Non-Surgical Procedures Help?
One of my recent patients was a 16-year female athlete who fractured her tibial plateau. She had a normal MRI, but her orthopedic surgeon’s exam pointed in the direction of posterior lateral corner injury. His solution was an exploratory surgery where he would likely perform a posterior lateral corner reconstruction. However, is this really needed?
I have treated dozens of patients in the last decade with posterior-lateral instability. Most don’t have dramatic MRI changes, but some have evidence of complete, but non-retracted tears in various ligaments. However, they are unstable on an exam. How do we treat this? We use precise x-ray and ultrasound-guided injections of platelet-rich plasma or bone marrow concentrate to spark healing in the damaged and stretched out PCL, tib-fib ligaments, popliteus, and LCL. These procedures have specific names (Perc-PLCR, Perc-tibiofibuloplasty, Perc-Popliteus Repair, and Perc-LCLR) and take significant expertise, but they usually result in the knee instability resolving without surgery. How does that work? The ligament fibers are stretched out and damaged and these substances can help these fibers heal.
The upshot? Posterior-lateral corner injury can be a big problem, but the good news is that most of these injuries don’t need surgery. Some will heal with bracing or physical therapy. We’ve been successful in treating these using precise injections of orthobiologics, but a few will require surgery.
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