A knee ligament tear can affect the knee’s stability, movement, and function. The symptoms can range from mild pain and swelling to significant instability that affects walking, sports, and everyday activities.
The knee has four main ligaments: the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). The medial patellofemoral ligament (MPFL) also plays an important role in stabilising the kneecap.
Each ligament injury can produce a different pattern of pain, swelling, instability, and movement difficulty. Recognising these symptoms can help you seek the right orthopaedic assessment at the right time.
The Ligaments of the Knee and Their Functions
Understanding each ligament’s role helps explain why different injuries produce different symptoms.
ACL
The anterior cruciate ligament helps prevent excessive forward movement of the tibia and provides rotational stability to the knee.
PCL
The posterior cruciate ligament prevents excessive backward movement of the tibia relative to the femur.
MCL
The medial collateral ligament supports the inner side of the knee and helps resist forces that push the knee inward.
LCL
The lateral collateral ligament stabilises the outer side of the knee and helps resist forces that push the knee outward.
MPFL
The medial patellofemoral ligament helps prevent the kneecap from moving too far towards the outer side of the knee.
What Causes a Knee Ligament Tear?
Ligament injuries usually occur when the force on the knee exceeds the ligament’s strength.
Common causes include:
- Sudden deceleration while changing direction
- Landing awkwardly after a jump
- Twisting the knee while the foot remains planted
- A direct blow to the knee
- Hyperextension of the knee
- Falls and sports-related injuries
- Motor vehicle injuries
- Sudden lateral displacement of the kneecap
ACL injuries are commonly associated with pivoting, sudden deceleration, and awkward landings. A direct blow to the front of a flexed knee can injure the PCL. MCL and LCL injuries are commonly associated with forces applied to the inner or outer side of the knee.
A sudden patellar dislocation can damage the MPFL and may result in recurrent kneecap instability.
How Are Knee Ligament Injuries Graded?
The severity of a ligament injury is generally described using three grades.
Grade 1: Sprain
The ligament fibres are stretched but remain intact. Symptoms usually include mild pain, tenderness, and limited swelling.
Grade 2: Partial Tear
Part of the ligament is damaged. Pain and swelling are usually more significant, and some looseness or instability may be present.
Grade 3: Complete Tear
The ligament is completely disrupted. The knee may feel unstable, particularly during activities involving turning, pivoting, or sudden changes in direction.
Treatment depends on the ligament involved, injury severity, associated damage, activity level, and the patient’s functional requirements.
Knee Ligament Tear Symptoms by Ligament
Different ligament injuries can produce different symptoms. The location and timing of pain and swelling can provide useful clues, although a proper clinical examination is required for diagnosis.
ACL Tear Symptoms
An ACL tear can occur during sports, falls, or sudden changes in direction.
Common symptoms include:
- A popping sensation at the time of injury
- Rapid swelling of the knee
- Pain and difficulty continuing the activity
- Reduced range of motion
- A feeling that the knee is giving way
- Instability during pivoting or turning
- Difficulty walking or returning to sports
A large knee swelling that develops soon after an injury, particularly when accompanied by a pop, requires prompt assessment for a possible ACL injury.
For more information about diagnosis and reconstruction, see ACL tear and reconstruction.
PCL Tear Symptoms
PCL injuries can sometimes be less obvious than ACL injuries, particularly when the PCL is injured in isolation.
Symptoms may include:
- Pain towards the back of the knee
- Swelling
- Difficulty walking downhill
- Difficulty using stairs
- Reduced knee movement
- A feeling of instability
- Posterior sag of the tibia in more significant injuries
Because PCL injuries can sometimes produce less dramatic symptoms, an assessment is important after a significant knee injury.
MCL Tear Symptoms
The MCL is located on the inner side of the knee. Its injury commonly produces:
- Pain along the inner side of the knee
- Localised swelling
- Tenderness over the ligament
- Pain when the knee is pushed inward
- A feeling of looseness in more severe injuries
MCL injuries can also occur together with ACL or meniscus injuries. A complete assessment is therefore important when the injury mechanism is significant.
LCL Tear Symptoms
The LCL is located on the outer side of the knee.
Symptoms may include:
- Pain on the outer side of the knee
- Tenderness around the LCL attachment
- Localised swelling
- A feeling of lateral instability
- Numbness or tingling around the outer leg in severe injuries
Because important nerves pass close to the outer side of the knee, numbness or weakness after a significant lateral knee injury requires prompt medical assessment.
MPFL Tear Symptoms
An MPFL tear commonly occurs following a patellar dislocation.
Typical symptoms include:
- The kneecap moving towards the outer side of the knee
- Pain along the inner side of the kneecap
- Knee swelling after the injury
- A feeling that the kneecap may slip again
- Fear or apprehension when straightening the knee
- Difficulty returning to sports or sudden changes of direction
Repeated kneecap instability may require assessment of the MPFL as well as the underlying knee anatomy.
Knee Ligament Tear or Muscle Tear: What Is the Difference?
Ligament injuries and muscle strains can sometimes feel similar, particularly during the early stages. Their location and symptoms can help distinguish them.
A ligament injury usually involves the structures that connect bone to bone and stabilise the knee. It may cause joint swelling, localised tenderness, and instability.
A muscle strain involves muscle fibres or the area where the muscle connects to the tendon. Pain is generally felt within the muscle rather than directly around the knee joint, and weakness may be more prominent than joint instability.
When the diagnosis is unclear, clinical examination and MRI can help identify the injured structure.
Torn Ligament in Knee Symptoms That Should Not Be Ignored
Some symptoms following a knee injury require timely orthopaedic assessment.
Seek medical evaluation when you experience:
- A pop followed by rapid knee swelling
- Severe pain after a twisting or contact injury
- Difficulty bearing weight
- A knee that repeatedly gives way
- Significant instability while walking
- A knee that locks and cannot fully straighten
- Numbness or weakness below the knee
- Persistent swelling after an injury
- Difficulty returning to normal activities after a knee injury
A large swelling that develops shortly after an injury can indicate bleeding inside the knee joint and may be associated with a significant ligament or other intra-articular injury.
How Is a Knee Ligament Tear Diagnosed?
An accurate diagnosis starts with a detailed clinical assessment, followed by imaging when required.
Clinical Examination
The orthopaedic assessment usually includes your injury history, pain location, swelling, movement limitations, previous injuries, and symptoms such as popping, clicking, catching, or locking.
Specific clinical tests can then help assess individual ligaments.
These may include:
- Lachman test for the ACL
- Anterior drawer test for the ACL
- Pivot shift test for rotational ACL instability
- Posterior drawer test for the PCL
- Posterior sag test for the PCL
- Valgus stress test for the MCL
- Varus stress test for the LCL
- Patellar apprehension test for MPFL-related instability
Dr. Amyn Rajani’s approach to knee assessment includes detailed history, clinical examination with special tests, and appropriate imaging.
You can also read about the clinical examination of the knee.
MRI and X-ray
MRI is useful for assessing ligaments, menisci, cartilage, and other soft tissues around the knee.
X-rays can help identify bone injuries, alignment problems, or avulsion fractures associated with some ligament injuries.
The choice of imaging depends on the injury mechanism, examination findings, and suspected structures involved.
Treatment Options for Knee Ligament Tears
Treatment depends on the ligament involved, injury severity, knee stability, associated damage, and the patient’s activity goals.
Conservative Treatment
Selected Grade 1 and Grade 2 ligament injuries can often be managed without surgery.
Treatment may include:
- Protection and activity modification
- Ice and compression during the early stage
- Knee bracing
- Physiotherapy
- Range of motion exercises
- Quadriceps and hamstring strengthening
- Balance and proprioception exercises
- Gradual return to normal activities
Rehabilitation plays an important role in both non-surgical and surgical treatment. Dr. Rajani’s knee rehabilitation programme includes physical therapy, physiotherapy, strengthening exercises, and appropriate knee supports.
Surgical Treatment
Surgery may be considered for significant instability, a complete tear in an active patient, recurrent patellar dislocation, combined ligament injury, or associated structural damage.
ACL reconstruction may be considered for active patients with symptomatic instability who want to return to pivoting sports. MPFL reconstruction may be considered for selected patients with recurrent patellar instability.
For MPFL injuries, treatment can range from conservative management and rehabilitation to reconstruction surgery depending on the injury and underlying anatomy.
Knee Ligament Tear Recovery
Recovery varies considerably depending on the ligament and injury severity.
Grade 1 collateral ligament injuries may recover within a few weeks. Grade 2 injuries generally require a longer rehabilitation period.
Recovery after ACL reconstruction usually takes several months, with return to competitive pivoting sports based on strength, stability, movement control, and functional assessment.
MPFL reconstruction also requires progressive rehabilitation before returning to demanding sports.
The goal is not simply to reduce pain. Rehabilitation aims to restore movement, muscle strength, balance, stability, and confidence in the knee.
Knee Rehabilitation After a Ligament Injury
A structured rehabilitation programme helps restore knee function and supports a safe return to daily activities or sport.
Depending on the injury, rehabilitation may include:
- Range of motion exercises
- Quadriceps strengthening
- Hamstring strengthening
- Hip strengthening
- Balance and proprioception training
- Progressive weight bearing
- Walking and movement retraining
- Sport-specific exercises
Dr. Rajani’s knee rehabilitation programme combines physical therapy, physiotherapy, strengthening, stretching, and appropriate knee supports based on the patient’s condition.
Patients can also refer to the knee rehabilitation exercise demonstration for examples of exercises used in knee rehabilitation.
Acute Knee Ligament Injury vs Chronic Instability
A ligament injury can remain symptomatic long after the initial pain and swelling have settled.
Acute Ligament Injury
An acute injury usually follows a specific incident such as twisting, landing, falling, or direct contact. Pain and swelling develop around the time of the injury.
Chronic Ligament Insufficiency
Chronic instability can develop when a ligament injury goes untreated or when the knee remains functionally unstable after the initial injury.
Patients may experience:
- Repeated episodes of giving way
- Instability during sports
- Difficulty with pivoting
- Activity-related swelling
- Reduced confidence in the knee
Repeated instability can place additional stress on other structures within the knee. Early assessment can help determine whether rehabilitation, bracing, or surgical treatment is appropriate.
Frequently Asked Questions
Can a torn knee ligament heal without surgery?
Some ligament injuries can heal with appropriate conservative treatment. Grade 1 and selected Grade 2 MCL and LCL injuries often respond well to rehabilitation and bracing. Treatment for ACL, PCL, and MPFL injuries depends on the severity, symptoms, stability, associated injuries, and activity requirements.
What is the difference between a muscle tear and a ligament tear?
A ligament connects bone to bone and provides joint stability. A muscle strain affects muscle fibres or the musculotendinous junction. Ligament injuries can cause joint instability, while muscle strains more commonly cause localised muscle pain and weakness.
How long does it take to recover from a knee ligament tear?
Recovery depends on the ligament and severity of the injury. Mild collateral ligament injuries may recover within a few weeks, while complete ACL or MPFL injuries requiring reconstruction may need several months of structured rehabilitation.
Do all knee ligament tears require surgery?
No. Many MCL and LCL injuries and selected PCL injuries can be managed conservatively. Surgery is considered when instability persists, the injury is severe, multiple ligaments are involved, or the patient’s functional requirements make reconstruction appropriate.
What does a knee ligament tear feel like?
The symptoms vary by ligament. An ACL tear may involve a pop, rapid swelling, and instability. An MCL tear usually causes pain along the inner side of the knee. A PCL injury may cause pain towards the back of the knee. An MPFL injury can cause kneecap instability after a patellar dislocation.
Are knee ligament injuries common in athletes?
Yes. Ligament injuries are an important category of sports-related knee injuries, particularly among athletes involved in football, cricket, badminton, basketball, and other activities involving running, jumping, pivoting, and sudden changes in direction.
