Reviewed by Dr Vishal Pai
A posterolateral corner (PLC) injury is damage to the group of ligaments and tendons that support the outer back corner of your knee. This page explains what the posterolateral corner is, how it gets injured, the symptoms, how the injury is diagnosed and treated, and when surgery is considered.
At a Glance
- The posterolateral corner is a group of ligaments, tendons and joint lining on the outer back corner of your knee. It stops the outside of the knee opening up and the shin bone twisting too far outwards.
- PLC injuries are uncommon on their own. Most happen together with a tear of the anterior or posterior cruciate ligament (ACL or PCL).[1]
- The main symptoms are pain on the outer side of the knee and a feeling that the knee gives way when you twist, turn or pivot.
- Mild and moderate injuries (grades I and II) are usually treated with a brace and physiotherapy.[2]
What is a posterolateral corner injury?
A posterolateral corner (PLC) injury involves damage to the joint lining, ligaments and tendons on the outside of the knee. “Posterolateral” means towards the back (posterior) and the outer side (lateral). The PLC is made up of the following structures:
- Posterolateral capsule (lining of the joint)
- Lateral collateral ligament
- Iliotibial band
- Popliteus tendon
- Popliteofibular ligament
- Biceps femoris tendon (hamstring)
- Lateral head of the gastrocnemius muscle (calf)
An injury to more than one of these structures is called a PLC injury. Three of them matter most for stability: the lateral collateral ligament, the popliteus tendon and the popliteofibular ligament. Together they stop the outside of the knee opening up when your leg is pushed into a bow-legged position (varus stress), and they stop your shin bone (tibia) rotating outwards on your thigh bone (femur).
How are PLC injuries graded?
- Grade I. The structures are stretched (sprained). The knee stays stable.
- Grade II. The structures are partly torn. The outside of the knee opens a little more than normal.
- Grade III. One or more structures are completely torn. The outside of the knee opens much more than normal and the knee feels unstable.
What causes a posterolateral corner injury?
A PLC injury usually happens when a force pushes the knee backwards and outwards, for example a blow to the inner front of the knee while the leg is straight. It can also happen when the knee bends too far backwards (hyperextends) or twists hard. Common causes include tackles in football and rugby, falls, and motorbike or car accidents.
Most PLC injuries come with other ligament tears. In an MRI study of 331 people with a recent knee injury and bleeding into the joint (haemarthrosis), 9.1% had a PLC injury, and 87% of those also had another ligament torn.[1] In another study of 162 people with an ACL rupture, about 1 in 5 also had damage to the posterolateral corner.[3] When two or more of the main knee ligaments are torn, it is called a multiligament injury.
What are the symptoms of a posterolateral corner injury?
PLC injuries can let the outside of the knee joint open abnormally. Because the PLC controls the rotation of the tibia on the femur, you may notice difficulty with twisting, turning and pivoting. Other symptoms include:
- Pain and swelling on the outer back corner of the knee
- Bruising behind or on the outer side of the knee
- The knee feeling loose or giving way, often when it is nearly straight
- The knee bending backwards further than the other one
- In older injuries, the knee pushing outwards with each step when you walk.
The force that causes this injury can sometimes stretch the common peroneal nerve, which wraps around the outside of the knee. This can weaken the muscles that lift your ankle and toes, causing a foot drop, and change the feeling in your foot.
When should you see a doctor?
See your GP or physiotherapist soon after any knee injury that leaves the knee loose or painful on the outside. Seek medical advice the same day if:
- Your knee gives way or feels loose on the outer side
- You cannot put weight on your leg
- You cannot lift your foot or toes, or your foot feels numb.
If your knee looks deformed after an injury, or your foot is cold, pale or very painful, go to an emergency department. These can be signs of a dislocated knee with damage to the blood supply.
How is a posterolateral corner injury diagnosed?
PLC injuries are easy to miss, especially when an ACL or PCL tear is the obvious injury. In one UK series of 68 people, 72% of PLC injuries were not recognised when the person was first seen.[5]
This injury can be detected on clinical examination. The doctor compares your knees: how far the outside of each knee opens when it is pushed inwards, and how far each shin bone turns outwards (the dial test). The injury is then investigated with an MRI scan, which is most accurate in the first weeks. Occasionally, stress X-rays are organised to measure how much the knee opens, and long-leg X-rays to check the alignment of your legs.[6]
How is a posterolateral corner injury treated without surgery?
Non-surgical treatment can be started if the structures of the PLC are sprained with no signs of instability on clinical examination. This covers grade I injuries and most grade II injuries, although some extra looseness can remain after a grade II injury.[2] Before choosing this path, your doctor needs to rule out a tear of the ACL, PCL or other ligaments.
Bracing
A hinged knee brace protects the outer side of the knee while the injured structures heal. You may need crutches for the first few days or weeks, depending on your pain and how stable the knee feels.
Physiotherapy
Treatment usually involves a period of bracing and rehabilitation with a physiotherapist. The program starts by restoring the range of movement, then builds strength in the thigh, hamstring and hip muscles and works on balance. Running, jumping and changing direction are added in stages.
Changing your activities
Avoid pivoting sports such as football, netball and basketball until your knee is stable and your strength is close to that of the other leg. Cycling, swimming and walking are usually fine earlier.
When is surgery considered?
Surgery is usually recommended for a complete (grade III) PLC injury, and when the PLC is torn along with the ACL or PCL. These injuries rarely heal well enough on their own. An untreated PLC tear can leave the knee unstable and can cause a new ACL or PCL graft to stretch or fail.[2][6] In people with multiligament injuries, a review found better results with surgery than without it, and with early surgery than with delayed surgery.[8] For this reason, surgery is usually done semi-urgently.
Surgery either repairs the torn structures or rebuilds them with a tendon graft (reconstruction). In a review of 12 studies of complete PLC injuries, repairs failed more often than reconstructions (22% compared with 7%).[9] Possible problems after surgery include knee stiffness, infection and nerve injury.[10] A torn cruciate ligament is often treated in the same operation. You can read more about ACL reconstruction and PCL reconstruction.
Next step
Have your knee assessed
If the outside of your knee feels unstable, surgery is usually done semi-urgently. Dr Vishal Pai can examine your knee, review your scans and explain your options.
What is the outlook for a posterolateral corner injury?
Most grade I and II injuries settle with a brace and physiotherapy. Athletes with a grade I or II lateral collateral ligament injury returned to sport after about two to three months in one series.[7]
For complete and combined injuries, surgery restores stability for most people, but not all. A nerve injury at the time of the original injury makes recovery slower and less complete.[4] Recovery after surgery takes many months, and your return to sport depends on which ligaments were injured.
References
Show all 10 referencesHide references
- LaPrade RF et al. 2007. A prospective magnetic resonance imaging study of the incidence of posterolateral and multiple ligament injuries in acute knee injuries presenting with a hemarthrosis. Arthroscopy.
- Covey DC. 2001. Injuries of the posterolateral corner of the knee. Journal of Bone and Joint Surgery (American).
- Temponi EF et al. 2017. Incidence and MRI characterization of the spectrum of posterolateral corner injuries occurring in association with ACL rupture. Skeletal Radiology.
- Kahan JB et al. 2020. The pathoanatomy of posterolateral corner ligamentous disruption in multiligament knee injuries is predictive of peroneal nerve injury. American Journal of Sports Medicine.
- Pacheco RJ et al. 2011. Posterolateral corner injuries of the knee: a serious injury commonly missed. Journal of Bone and Joint Surgery (British).
- LaPrade RF et al. 2025. A contemporary international expert consensus statement on the evaluation, diagnosis, treatment, and rehabilitation of injuries to the posterolateral corner of the knee. Arthroscopy.
- Haslhofer D et al. 2025. Isolated clinically diagnosed grades 1-2 lateral collateral ligament injuries in elite athletes do not require surgery. Orthopaedic Journal of Sports Medicine.
- Levy BA et al. 2009. Decision making in the multiligament-injured knee: an evidence-based systematic review. Arthroscopy.
- Fortier LM et al. 2023. Higher success rate observed in reconstruction techniques of acute posterolateral corner knee injuries as compared to repair: an updated systematic review. Knee Surgery, Sports Traumatology, Arthroscopy.
- Maheshwer B et al. 2021. Incidence of intraoperative and postoperative complications after posterolateral corner reconstruction or repair: a systematic review of the current literature. American Journal of Sports Medicine.
Frequently asked questions
What does "posterolateral" mean?
Posterior means towards the back and lateral means towards the outer side, so posterolateral means the outer back part. The posterolateral corner of the knee is the outer back corner, where the lateral collateral ligament, the popliteus tendon and the popliteofibular ligament sit.
Is a PLC injury the same as an LCL injury?
Not quite. The lateral collateral ligament (LCL) is one part of the posterolateral corner. It can be injured on its own, and mild LCL injuries are usually treated without surgery.[7] When other PLC structures are torn as well, the knee can also become loose when it twists. You can read more about LCL injuries.
Can a posterolateral corner injury heal without surgery?
Will an MRI show a posterolateral corner injury?
Usually, if the scan is done soon after the injury. In one series, MRI showed the injury in 14 of 15 people scanned within 12 weeks, but in only 4 of 15 scanned later.[5] The examination matters as much as the scan, and stress X-rays can help measure how loose the knee is.
What is posterolateral corner surgery?
It is an operation to repair the torn structures or rebuild them with a tendon graft. For complete tears treated soon after injury, reconstruction failed less often than repair in a review of 12 studies.[9] Dr Vishal Pai can explain which option suits your injury and whether any other ligaments need treatment at the same time.