Posterolateral corner injury of the knee refers to damage to the group of ligaments, tendons and soft tissues on the outside-back part of the knee. This area is often called the posterolateral corner, or PLC. The PLC helps stop the knee from bowing outwards, twisting excessively, or giving way backwards. When it is injured, people often describe outer knee pain, swelling, instability, a feeling that the knee “opens up”, or difficulty trusting the knee during walking, sport, stairs, slopes or change of direction.
The main structures involved in a posterolateral corner knee injury include the fibular collateral ligament, popliteus tendon, popliteofibular ligament, biceps femoris tendon, posterolateral capsule and nearby nerves. These structures work together with the anterior cruciate ligament and posterior cruciate ligament to control knee stability. This is why PLC injuries are commonly seen with ACL tears, PCL tears, knee dislocations or multiligament knee injuries.
Physiotherapy for posterolateral corner injury is important because the condition affects far more than one ligament. A physiotherapist assesses knee stability, swelling, walking pattern, quadriceps strength, hamstring control, hip strength, balance, running mechanics and return-to-sport readiness. In mild injuries, posterolateral corner injury physiotherapy exercises may be the main treatment. In severe injuries or post-surgical cases, physiotherapy guides safe loading, protects healing tissue, restores strength and helps the person return to work, sport or daily activity with less risk of reinjury.
A PLC injury should not be ignored. Untreated posterolateral instability can place extra strain on the cruciate ligaments and may contribute to persistent giving way, ongoing pain, poor confidence and failure of ACL or PCL grafts. Early assessment by a physiotherapist, sports doctor or orthopaedic specialist is especially important if the injury involved a high-force accident, a knee dislocation, major swelling, numbness, foot weakness, or obvious instability.
Key Facts
- Posterolateral knee injuries have been reported to account for 16% of knee ligament injuries and 9.1% of acute knee injuries with haemarthrosis, with 87% of PLC injuries in that cohort occurring with multiple ligament injury. 🔗
- In a study of grade 3 posterolateral corner injuries, the most common associated ligament pattern was ACL plus PLC injury, seen in 56.4% of knees, followed by ACL, PCL and PLC injury, seen in 35.9% of knees. 🔗
- A two-centre outcomes study of 64 patients with grade 3 chronic posterolateral instability found that anatomic posterolateral knee reconstruction improved clinical outcomes and objective stability. 🔗
Risk Factors
- Contact sports such as rugby, Australian rules football, soccer, martial arts and American football
- Sports involving cutting, pivoting, skiing, jumping or rapid deceleration
- Previous ACL, PCL or multiligament knee injury
- Previous knee dislocation or major knee trauma
- Poor landing mechanics, especially landing with the knee collapsing, twisting or hyperextending
- Weak quadriceps, gluteal and calf muscles, which can reduce control of knee position
- Poor balance and single-leg control after a previous knee injury
- Returning to sport before completing strength, hopping, running and change-of-direction testing
- High-speed trauma such as motor vehicle, motorcycle or cycling accidents
- Generalised joint laxity or naturally increased knee hyperextension
Symptoms
- Pain on the outside-back part of the knee, especially near the fibular head
- Swelling after a twisting, hyperextension, tackle, fall or road accident
- A feeling that the knee gives way, shifts, opens up or cannot be trusted
- Difficulty walking on uneven ground, slopes, stairs or when turning quickly
- Instability when pivoting, sidestepping, landing, decelerating or changing direction
- Pain or apprehension when the knee is forced into a bow-legged position
- Weakness or poor control when standing on one leg
- Reduced knee range of motion due to swelling, pain or guarding
- Tenderness along the outside of the knee or upper fibula
- Bruising around the outside or back of the knee after acute trauma
- Numbness, tingling, burning or altered sensation down the outside of the leg or top of the foot if the peroneal nerve is irritated
- Foot drop, toe lifting weakness or difficulty clearing the foot when walking in more serious nerve-related injuries
Aggravating Factors
- Walking on uneven ground where the knee has to make small rotational corrections
- Side-stepping, cutting, pivoting or twisting during sport
- Running downhill or decelerating quickly
- Landing from a jump with the knee drifting outwards or backwards
- Contact to the inner side of the knee, which pushes the knee into varus
- Hyperextension movements, especially when combined with twisting
- Deep squats, lunges or loaded knee bending early after injury
- Stairs, slopes and getting in or out of a car when the knee feels unstable
- Returning to sport before strength, balance and rotational control have been restored
- Poorly controlled hamstring loading after PLC reconstruction, particularly if the surgeon has restricted early hamstring use
Causes
A posterolateral corner injury usually occurs when the knee is forced into a position that overloads the outside-back stabilisers. The most common mechanisms include a blow to the inside of the knee, a varus force where the knee bows outwards, a hyperextension injury, or a twisting injury where the shin rotates outwards. In sport, this can happen during a tackle, awkward landing, sidestep, collision, fall, skiing injury, rugby or football contact, or sudden change of direction. Outside sport, PLC injuries may occur during motor vehicle accidents, motorcycle accidents, falls from a height or knee dislocations.
The posterolateral corner is rarely injured in isolation when the trauma is severe. It often occurs with ACL injury, PCL injury, meniscus tears, cartilage injury, fractures, bone bruising or peroneal nerve irritation. This combined injury pattern is why physiotherapy assessment for posterolateral corner injury must look beyond the painful area. A physiotherapist will assess the whole knee, hip, ankle, gait, swelling, nerve symptoms and functional stability.
Milder PLC sprains may involve stretching or partial tearing of the lateral and posterolateral structures. These injuries may respond well to bracing, activity modification and posterolateral corner injury physiotherapy exercises. More severe injuries can involve complete rupture or avulsion, where the ligament or tendon pulls away from bone. These injuries are more likely to require orthopaedic review and sometimes surgical repair or reconstruction, followed by structured posterolateral corner injury rehab.
How Is It Diagnosed?
Diagnosis starts with a careful history. A physiotherapist will ask how the injury happened, whether there was a pop, swelling, giving way, locking, numbness, tingling, foot weakness or a feeling that the knee shifted out of place. The mechanism is important because a direct blow to the inside of the knee, a hyperextension episode, or a twisting injury with external rotation can all point towards a posterolateral corner injury.
Physical examination usually includes observation of swelling, bruising, walking pattern, knee alignment and range of motion. A physiotherapist may palpate the fibular head, lateral joint line, biceps femoris tendon and posterolateral knee structures. Strength testing is used to assess quadriceps, hamstrings, calf, hip abductors and hip rotators. Neurological screening is also important because the common peroneal nerve runs near the fibular head and can be affected in significant PLC injuries.
Specific clinical tests may include varus stress testing at different knee angles, the dial test, posterolateral drawer test, reverse pivot shift test and assessment for associated ACL or PCL injury. These tests help determine whether there is lateral instability, external rotation instability, posterior instability or a combined multiligament pattern. In an acute painful knee, some tests may be limited by swelling and guarding, so reassessment over time is often required.
A physiotherapist may refer for imaging or medical review if there is marked instability, suspected complete rupture, inability to weight bear, major swelling, nerve symptoms, suspected fracture, or a suspected ACL, PCL or multiligament injury. Early diagnosis matters because missed PLC injuries can lead to long-term instability and may compromise outcomes after ACL or PCL reconstruction.
Investigations & Imaging
- X-ray
- Used after traumatic knee injury to check for fracture, avulsion injury near the fibular head, joint alignment, knee dislocation signs or associated bony injury.
- Magnetic resonance imaging
- Used to assess the fibular collateral ligament, popliteus tendon, popliteofibular ligament, biceps femoris tendon, posterolateral capsule, menisci, cartilage, bone bruising, ACL, PCL and other soft tissues.
- Varus stress X-rays
- May help quantify lateral joint opening and compare side-to-side laxity, particularly when a complete fibular collateral ligament or posterolateral corner injury is suspected.
- Long-leg alignment X-ray
- May be used in chronic posterolateral instability to assess limb alignment, especially if varus alignment is contributing to ongoing load on the outside of the knee.
- Computed tomography
- May be used when fracture, avulsion, complex bony injury or surgical planning needs clearer bone detail.
- Nerve conduction studies
- May be considered when there is persistent peroneal nerve weakness, numbness, tingling or foot drop after a posterolateral corner injury.
Grading / Classification
- Grade I
- A mild sprain where the posterolateral structures are stretched but not significantly torn. Pain and tenderness may be present, but there is usually minimal instability. Physiotherapy for posterolateral corner injury often focuses on swelling control, restoring motion, gradual strengthening and safe return to activity.
- Grade II
- A partial tear with increased pain, swelling and some laxity. The knee may feel less secure with twisting, slopes or sport. Management may include bracing, activity modification and a structured PLC rehab program, with referral if instability is significant or associated ligament injury is suspected.
- Grade III
- A complete tear or major disruption of the posterolateral corner. There is usually clear instability, increased varus or rotational laxity, and a higher likelihood of ACL, PCL, meniscus, cartilage or nerve involvement. Orthopaedic review is commonly required, and many grade 3 injuries need surgical repair or reconstruction followed by detailed physiotherapy rehabilitation.
Physiotherapy Management
Exercise
Exercise is central to physiotherapy for posterolateral corner injury, but the right exercises depend on the grade of injury, associated ligament damage and whether surgery has been performed. Early posterolateral corner injury physiotherapy exercises often focus on reducing swelling, restoring comfortable knee motion, reactivating the quadriceps and improving walking mechanics. This may include quadriceps sets, straight leg raises, supported knee bends, calf activation and gentle hip strengthening.
As symptoms settle, physiotherapy progresses towards controlled strengthening of the quadriceps, gluteals, calf and hip muscles. These muscles help control knee position and reduce excessive varus or twisting load through the posterolateral knee. Exercises may include leg press within a safe range, step-ups, sit-to-stand drills, bridges, hip abduction work, calf raises and balance drills. Hamstring loading may need to be delayed or modified in some PLC injuries, particularly after reconstruction, because the biceps femoris and posterolateral structures can be involved.
Later-stage PLC rehab includes single-leg strength, landing control, hopping, acceleration, deceleration, cutting and sport-specific drills. A physiotherapist will usually compare strength and hop performance with the uninjured side before return to running or sport. For athletes, posterolateral corner injury rehab should include fatigue-based testing because instability often becomes more obvious when the hip and thigh muscles tire.
Activity Modification
Activity modification protects the healing posterolateral corner while allowing the rest of the body to stay active. In the early phase, a physiotherapist may advise avoiding pivoting, side-stepping, running, uneven ground, deep squats, loaded twisting and hyperextension positions. The aim is not complete rest for every person, but rather choosing activities that do not repeatedly open or rotate the injured side of the knee.
For mild injuries, this may mean temporarily switching from running to cycling, pool walking or upper-body conditioning. For more severe injuries, crutches and a brace may be required to limit load and protect against giving way. A physiotherapist will help progress weight bearing, walking distance, stairs, gym training and work duties based on pain, swelling, stability and medical restrictions.
Manual Therapy
Manual therapy may be used by a physiotherapist to address pain, stiffness and protective muscle guarding after a PLC injury. It may include soft tissue techniques around the quadriceps, calf, hamstrings, iliotibial band and hip, as well as joint mobilisation to restore knee extension or flexion when appropriate. Manual therapy does not “repair” a torn posterolateral corner, but it can help the person move better and tolerate exercise during rehab.
In post-surgical PLC rehab, manual therapy must respect graft protection and surgeon instructions. Aggressive stretching, forced knee extension, or techniques that place varus or rotational stress on the knee are usually avoided early. The physiotherapist’s goal is to improve movement without stressing the healing structures.
Postural Retraining
Postural and movement retraining is highly relevant because PLC symptoms are often provoked by poor control of knee alignment. A physiotherapist will assess whether the knee drifts into hyperextension, varus, excessive rotation or poor single-leg alignment during standing, squatting, walking, stair descent, landing or running. Even small faults can matter when the posterolateral stabilisers are healing.
Retraining may involve teaching a softer knee position during standing, improving hip control during single-leg tasks, correcting foot placement during turning, and improving trunk position during landing or cutting. For athletes, this becomes more advanced and may include change-of-direction technique, tackling mechanics, skiing stance, running deceleration and reactive agility drills.
Bracing & Taping
Bracing is commonly used in posterolateral corner injury management, especially when there is instability or after surgery. A hinged knee brace may help limit varus stress, twisting and hyperextension while the injured tissues heal. In some post-operative protocols, bracing and restricted weight bearing are used for several weeks, but exact timelines depend on the surgeon’s instructions and associated injuries.
Taping may be used by a physiotherapist as a short-term support strategy for mild injuries or during the transition back to activity. It can improve confidence and body awareness, but it is not a substitute for strength, balance and proper knee control. For a complete PLC tear, taping alone is not enough to stabilise the knee.
Heat & Ice
Ice may help reduce pain and swelling in the early phase after a posterolateral corner knee injury, particularly after activity or physiotherapy exercises. It can be useful when the knee feels hot, puffy or reactive. Heat is usually more helpful later when there is muscle tightness or stiffness around the thigh, calf or hip, but it should not be used as the main treatment for an unstable knee.
A physiotherapist may recommend ice or heat as part of symptom management, but long-term improvement depends on restoring knee stability, strength, balance, range of motion and confidence.
Education
Education is a major part of physiotherapy for posterolateral corner injury. Many patients are told they have a “lateral knee sprain” without understanding that the PLC controls important rotational and side-to-side stability. A physiotherapist explains the injury, expected healing time, safe positions, bracing instructions, exercise progression and signs that need medical review.
Education also includes return-to-sport planning. A person should not return to pivoting sport simply because pain has settled. The knee needs adequate strength, control, agility, confidence and no giving way. For work-related injuries, physiotherapy education may include safe kneeling, lifting, ladder use, uneven ground management and staged return to physical duties.
Other
Gait retraining is often required because people with PLC injuries may walk with a stiff knee, reduced push-off, poor knee extension control or a subtle thrust into varus. A physiotherapist may use walking drills, crutch retraining, treadmill feedback or step practice to restore a smoother gait pattern.
Balance and proprioception training are also important. Proprioception is the body’s ability to sense joint position. After a ligament injury, the knee may not send clear stability signals to the brain. Balance drills, perturbation training and reactive control exercises help rebuild this system and are especially important before returning to sport or uneven outdoor activity.
Other Treatments
Medication may be used to manage pain and swelling after a PLC injury, but it does not restore mechanical stability. A GP or sports doctor may advise simple pain relief or anti-inflammatory medication when appropriate. In more significant trauma, medical assessment is required to exclude fracture, vascular injury, nerve injury or knee dislocation.
Injections are not a primary treatment for posterolateral corner ligament injury. They may occasionally be considered when there is associated joint irritation or another diagnosis contributing to pain, but they do not heal a complete PLC tear or correct instability. A physiotherapist can help determine whether pain is mainly from the ligament injury, swelling, altered mechanics, muscle overload or another knee structure.
For severe multiligament injuries, care may involve a team including a physiotherapist, sports physician, orthopaedic surgeon, radiologist and, when nerve symptoms are present, a neurologist or peripheral nerve specialist. This team approach is particularly important when there is foot drop, ongoing numbness, suspected vascular involvement or complex return-to-work or return-to-sport demands.
Surgery
Surgery may be recommended for grade 3 posterolateral corner injuries, combined ACL or PCL injuries, knee dislocations, significant varus or rotational instability, bony avulsions, or cases where the knee continues to give way despite appropriate conservative care. Surgical management may involve repair, reconstruction, or a combination of both. Repair is more likely when a structure has pulled off the bone and can be reattached. Reconstruction is often used when the ligament or tendon is torn through the middle or when the injury is chronic.
PLC reconstruction aims to restore the stabilising role of the fibular collateral ligament, popliteus tendon and popliteofibular ligament. If the ACL or PCL is also torn, surgery may be staged or performed together depending on the injury pattern, swelling, stiffness, surgeon preference and patient goals.
Physiotherapy after posterolateral corner surgery is essential. Early rehabilitation usually focuses on protecting the reconstruction, controlling swelling, regaining safe knee motion and maintaining quadriceps activity. Weight bearing, brace use, knee flexion limits and hamstring restrictions vary depending on the surgical technique and associated injuries. Later rehabilitation progresses towards strength, balance, running, agility and return-to-sport testing. A rushed return can overload the graft or leave the person with persistent instability.
Prognosis & Return to Activity
Prognosis depends on the grade of the posterolateral corner injury, whether it is isolated or combined with ACL, PCL, meniscus, cartilage or nerve injury, how quickly it is diagnosed, and whether the knee is mechanically stable. Mild grade 1 injuries may settle with physiotherapy, bracing and progressive strengthening over weeks. Grade 2 injuries can take longer and need careful progression to avoid recurrent giving way. Grade 3 injuries often require surgical opinion, and recovery is usually measured in months rather than weeks.
Return to daily walking usually comes before return to running. Running generally requires minimal swelling, full or near-full range of motion, good quadriceps control, no giving way and adequate single-leg strength. Return to sport requires a higher standard. A physiotherapist will usually assess jumping, hopping, cutting, deceleration, balance, strength symmetry and confidence before clearing pivoting or contact sport.
For athletes after PLC reconstruction, return to sport is commonly a long rehabilitation process. It must be based on objective criteria rather than time alone. The person should demonstrate strong quadriceps and hip control, good landing mechanics, no instability, no reactive swelling and the ability to complete sport-specific drills under fatigue. Incomplete rehab can leave the knee vulnerable to reinjury or overload of the ACL, PCL or reconstructed posterolateral structures.
Complications
- Chronic posterolateral knee instability with ongoing giving way
- Persistent outer knee pain during walking, sport or stairs
- Reduced confidence with pivoting, landing or uneven ground
- Increased strain on the ACL, PCL or previous cruciate ligament graft
- Peroneal nerve irritation, numbness, tingling or foot drop in more severe injuries
- Stiffness after injury or surgery, especially if swelling and motion are not managed well
- Ongoing quadriceps weakness and poor single-leg control
- Meniscus or cartilage overload due to altered knee mechanics
- Delayed return to sport or physical work
- Recurrent injury if the person returns to cutting or contact sport before completing PLC rehab
Preventing Recurrence
- Complete a full posterolateral corner injury rehab program before returning to pivoting, cutting or contact sport, rather than stopping when pain first improves.
- Build quadriceps, gluteal, calf and trunk strength so the knee is better controlled during landing, deceleration and change of direction.
- Practise landing and sidestepping technique with a physiotherapist to reduce hyperextension, varus collapse and excessive shin rotation.
- Avoid early return to uneven ground, downhill running or lateral agility drills if the knee still feels unstable or swollen.
- Avoid early return to uneven ground, downhill running or lateral agility drills if the knee still feels unstable or swollen.
- Avoid early return to uneven ground, downhill running or lateral agility drills if the knee still feels unstable or swollen.
- Progress running and sport gradually, using strength and hop testing rather than relying on time alone.
- Maintain hip and ankle mobility so the knee does not compensate with excessive twisting during sport or work tasks.
- Avoid fatigue-based technique breakdown by including conditioning and late-session movement control in return-to-sport physiotherapy.
- Seek early physiotherapy review after any new giving way episode, especially if it occurs with swelling or outer knee pain.
When to See a Physio
- You feel pain on the outside-back of the knee after a twisting, hyperextension, tackle or fall.
- Your knee feels unstable, loose, wobbly or like it may give way.
- You have swelling after a knee injury, especially if it developed quickly.
- You are struggling with stairs, slopes, uneven ground or turning while walking.
- You have been diagnosed with an ACL or PCL injury and want the posterolateral corner assessed as well.
- You are wearing a brace and need guidance on safe walking, strengthening and return to activity.
- You are recovering after PLC repair or reconstruction and need a structured physiotherapy program.
- You have ongoing knee instability after a previous ligament injury or reconstruction.
- You are planning to return to sport and need strength, hop, balance and agility testing.
- You have numbness, tingling, burning, foot weakness or difficulty lifting your toes after a knee injury.