Introduction
Knee injuries are common in sports and daily life, and the most serious involve damage to the stabilizing ligaments of the knee. The knee has four primary ligaments – the Anterior Cruciate Ligament (ACL), Posterior Cruciate Ligament (PCL), Medial Collateral Ligament (MCL), and Lateral Collateral Ligament (LCL). This article focuses on the differences between ACL, PCL, and LCL tears, detailing how each injury occurs, their symptoms, and how they are treated. Understanding these differences is crucial for proper diagnosis and management.
Not all knee ligament injuries are equally common. In fact, an ACL tear is the most frequently seen knee ligament injury. PCL injuries are less common because the PCL is thicker and stronger than the ACL , and LCL tears are among the least common isolated ligament injuries in the knee. Despite differences in frequency, any of these ligament tears can cause pain, instability, and difficulty with knee movement.
What is an ACL Tear?
The ACL (located in the center of the knee) is one of the two cruciate ligaments that cross inside the knee joint, forming an “X.” It connects the femur (thigh bone) to the tibia (shin bone) and prevents the tibia from sliding too far forward, while also providing rotational stability. In other words, the ACL keeps the knee from buckling during pivoting or sudden stops.
How ACL Tears Occur: ACL tears often happen during sports or activities that involve sudden stops, pivots, or jumps. A typical scenario is a quick change of direction or an awkward landing from a jump that puts a twisting force on the knee (common in sports like soccer, basketball, or volleyball). Direct blows to the knee (for example, during a football tackle) can also cause ACL injuries, though most ACL tears are non-contact injuries from sudden deceleration or cutting movements.
Symptoms of an ACL Tear: When the ACL tears, people often report feeling or hearing a loud “pop” at the moment of injury. This is usually followed by immediate pain and swelling in the knee. The person typically cannot continue activity due to the knee giving way. There is often a sense of instability or wobbliness – the knee might feel like it can’t support weight or might buckle during twisting movements. Swelling develops rapidly (within the first few hours) because ACL tears cause bleeding inside the joint, leading to a tense, swollen knee. Loss of full range of motion is common in the acute phase due to pain and swelling.
Treatment: The ACL does not heal on its own (it has a poor blood supply inside the joint), so a complete ACL tear in an active individual often requires surgical reconstruction. In an ACL reconstruction, the surgeon replaces the torn ligament with a graft. This surgical reconstruction is often recommended for active individuals to restore knee stability (see our guide on ACL reconstruction and meniscus repair for details on the procedure). After surgery, a rigorous rehabilitation program is needed (typically 6–9 months of rehab) before returning to high-impact activities. Some people who are older or less active may opt to not have surgery and instead manage with bracing and physical therapy – this can stabilize the knee for daily activities, but the knee may remain too unstable for sports. (For more on ACL injury severity and management, see our in-depth guide on ACL tear grades and treatment.)
What is a PCL Tear?
The PCL (located at the back of the knee) is the partner to the ACL and is the other cruciate ligament inside the joint. It connects the femur to the tibia and prevents the tibia from sliding backward under the femur. The PCL is thicker and stronger than the ACL, so it’s less frequently torn. Together with the ACL, the PCL keeps the knee stable during front-to-back motions and deep knee bends.
How PCL Tears Occur: PCL injuries typically happen from a significant force while the knee is bent. A classic mechanism is the “dashboard injury” – during a car accident, if the knees are bent and the dashboard or other object strikes the shin, it can push the tibia backward and tear the PCL. Another common cause is a fall onto a bent knee with the foot pointed downward, which drives the tibia backward (for example, a rough landing in sports or a hard fall in wrestling/rugby). PCL tears can also occur in football or soccer from a hard blow to the front of the knee or a severe hyperextension, but isolated PCL tears are uncommon in sports. Often, PCL injuries occur along with other ligament damage if the knee sustains a major trauma.
Symptoms of a PCL Tear: A PCL tear might not be as dramatic as an ACL tear. There may be no audible pop. Pain is usually felt in the back of the knee (in the area behind the knee joint). Swelling can occur, sometimes quickly, but sometimes more gradually over the next day. Many PCL tears are partial tears, so the knee may feel only mildly unstable – perhaps a sense of looseness or slight slipping, especially when walking downhill or descending stairs. Some people with a PCL injury can still walk on the injured leg (after the initial pain subsides), often with a bit of stiffness or a limp. Key signs of a PCL tear include posterior knee pain, swelling, and difficulty with activities like going down ramps or stairs (because the tibia can slide back more than normal). If the PCL is completely torn and especially if other structures are injured, the knee could exhibit significant instability (it might sag backwards noticeably when bent – a sign doctors call “posterior sag”).
Treatment: Most PCL tears (especially partial tears) are managed conservatively without surgery. The PCL, like the ACL, won’t reliably heal back together on its own, but if the knee is stable enough, doctors opt for non-surgical treatment. This typically involves using a brace that supports the knee (often a PCL-specific brace that holds the tibia forward) and a structured physical therapy program to strengthen the quadriceps and other muscles that help stabilize the knee. Over a few months, a partial PCL tear can scar in and the knee may become stable again. Surgery for a PCL tear is usually reserved for cases where the PCL is completely torn and the knee is very unstable, or when there are multiple ligament injuries at once (for example, PCL plus LCL/ACL tears). In those situations, a PCL reconstruction (replacement of the ligament with a graft) is performed. If PCL surgery is needed, the recovery and rehab often takes a similar length of time as ACL surgery (around 6–9 months of intensive rehabilitation). (Learn more about our approach to PCL injury diagnosis and treatment in our educational resources.)
What is an LCL Tear?
The LCL is one of the two collateral ligaments of the knee. Collateral ligaments are found on the sides of your knee and act like strong stabilizing straps to prevent excessive side-to-side motion. The LCL runs along the outer side of the knee, connecting the femur (thigh bone) to the fibula (the smaller bone on the outer lower leg). Its job is to stabilize the outer knee and prevent the joint from opening up outward (varus force). Essentially, the LCL keeps your knee from bowing outwards.
How LCL Tears Occur: Isolated LCL injuries are relatively uncommon because they usually require a high-force impact. The typical cause is a blow to the inner side of the knee that forces the knee outward (a varus force). This often happens in contact sports. For example, a football or rugby tackle that hits the inside of the knee can injure the LCL. (In some sports like wrestling or kabaddi, falls or collisions can similarly put stress on the inner knee.) LCL tears can also occur during motorcycle or bicycle accidents where the knee gets twisted or a force drives the knee outward. Often, when the LCL is torn in a high-impact injury, other structures such as the ACL, PCL, or the corner of the knee joint (posterolateral corner) may be injured at the same time due to the overall force involved.
Symptoms of an LCL Tear: An LCL injury causes pain on the outer side of the knee, directly over the area of the ligament. You’ll likely see swelling and sometimes bruising along the outer knee. Instability with side-to-side motion is a key sign – if an LCL tear is significant, the knee may feel like it “gives way” when a sideways (varus) force is applied, such as if you try to change direction quickly or if someone pushes against the inner knee. In a partial LCL tear, you might only notice pain and slight looseness when the knee is stressed inward, and you may still be able to walk on it, albeit carefully. In a complete LCL tear, the lateral instability is more obvious: the knee can feel very loose or wobbly in sideways movements. Often within a week of an LCL injury, patients can walk with a bit of a limp as pain subsides, but they may feel that the knee is not stable for twisting or side-stepping actions.
Treatment: The treatment for an LCL tear depends on its severity. Partial LCL tears (Grades I and II sprains) are usually treated successfully with conservative care. This includes the R.I.C.E. protocol (Rest, Ice, Compression, Elevation) initially and use of a hinged knee brace to protect the outer knee from stress while the ligament heals. Because the LCL is outside the joint capsule and has a decent blood supply, it can heal naturally if the knee is kept stable – often, bracing for a few weeks allows a partial tear to scar and mend. During this time, physical therapy focuses on maintaining range of motion and then strengthening the muscles around the knee (especially the hamstrings and hip muscles that support lateral stability). Complete LCL tears (Grade III), especially if they result in significant instability or occur in combination with other ligament injuries, often require surgical repair or reconstruction. In surgery, the torn LCL is either stitched back or replaced with a graft to restore stability. After an LCL surgery, the knee will be braced and a structured rehab program is important – recovery from LCL reconstruction can take on the order of 4–6 months before returning to full activities. Early treatment is important; if a completely torn LCL is left untreated, the chronic instability can lead to cartilage wear and knee arthritis down the line. (Learn more in our dedicated guide on LCL injury causes, symptoms, and treatments.)
Key Differences Between ACL, PCL, and LCL Tears
While ACL, PCL, and LCL tears are all injuries to knee ligaments, there are important distinctions in terms of location, common causes, symptoms, and recovery. Below is a summary of the key differences:
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Location & Function: The ACL and PCL are located inside the knee joint (they are cruciate ligaments that form an “X” in the middle of the knee) and primarily control front-to-back stability and rotation. The ACL prevents the tibia from sliding forward and limits rotational stress, whereas the PCL prevents the tibia from sliding backward. The LCL, on the other hand, is a collateral ligament on the outside of the knee. It connects the femur to the fibula and stabilizes against lateral forces (preventing the knee from bending outward). This means ACL/PCL injuries affect front-back and pivoting stability, while an LCL injury affects side-to-side (outer) stability. Another difference is blood supply and healing environment – the ACL and PCL are inside the joint capsule (bathed in joint fluid) and have a poor blood supply, so they do not heal well on their own. The LCL is outside the joint capsule and has a better blood supply, giving it some capacity to heal if the tear is not severe.
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Frequency of Injury: ACL tears are by far the most common of these three injuries in athletes. The ACL’s role in high-speed cutting and pivoting motions makes it vulnerable, and it’s often injured in sports like soccer, basketball, and football. PCL tears are much less common – they account for a smaller percentage of knee injuries (fewer than 20% of knee ligament injuries involve the PCL only) because the PCL’s greater strength means it typically requires a high-impact trauma to tear. LCL tears are the least common as isolated injuries. It usually takes a significant impact to the inside of the knee to tear the LCL, and such impacts often injure other ligaments at the same time. In summary, if someone has a knee ligament tear from sports, it’s most likely ACL; PCL and especially LCL tears are relatively rarer without major trauma.
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Cause of Injury: An ACL tear usually results from a sudden pivot or awkward landing – for example, changing direction quickly or landing from a jump and twisting the knee can tear the ACL (common in soccer, basketball, volleyball). ACL injuries can also happen from a direct blow (like a tackle to the knee) but non-contact twists are more typical. A PCL tear often requires a direct force on a bent knee. Common causes are car accidents (knees hitting the dashboard), a hard fall onto a bent knee, or a blow to the front of the shin in sports. In other words, PCL injuries often involve the tibia being pushed backward. LCL tears are caused by a force that pushes the knee outward. The classic scenario is a blow to the inner knee (for instance, a football tackle hitting the inside of the knee). That inward-to-outward stress on the knee can sprain or tear the LCL. So, while ACL injuries are often non-contact and involve rotation, PCL injuries are usually from front-to-back force on a bent knee, and LCL injuries come from side-to-side force (impact to the opposite side of the knee).
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Symptoms & Instability: All three injuries cause knee pain and swelling, but their specific symptoms and degree of instability differ:
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ACL tear: Often marked by a loud “pop” at the moment of injury, followed by immediate swelling. An ACL tear typically causes severe pain and an unstable knee that gives way if you try to pivot or continue activity.
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PCL tear: May not produce a pop sound, and the initial pain can be relatively mild. Swelling still occurs (sometimes rapidly), but instability is usually less pronounced – you might only feel the knee give out during certain movements like going downstairs or decelerating, since many PCL tears are partial.
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LCL tear: Causes pain on the outer side of the knee along with outer-knee swelling or bruising. The key sign is lateral instability; the knee may wobble or feel loose if pushed inward (a varus force). Minor LCL sprains might only hurt with side stress, but a complete LCL tear can lead to significant sideways knee instability.
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Treatment & Healing: Healing potential and typical management differ for each ligament:
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ACL: A torn ACL will not heal on its own, so a complete ACL rupture usually requires surgical reconstruction to restore stability (especially for younger or athletic patients).
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PCL: The PCL also has limited self-healing, but because many PCL tears are partial, they are often managed with bracing and physical therapy instead of surgery. Surgery is reserved for PCL tears that cause severe instability or are combined with other ligament injuries.
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LCL: The LCL, being outside the joint capsule, can sometimes heal naturally. Partial LCL tears often heal with a few weeks of bracing. However, a completely torn LCL (especially if other ligaments are also torn) usually needs surgical repair to restore knee stability.
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Recovery Time: The rehabilitation timelines vary depending on the ligament and whether surgery is required. ACL tears often have the longest recovery. After ACL reconstruction surgery, it typically takes about 9–12 months of rehab to return to high-level sports. Without surgery (for example, if an ACL tear is managed conservatively for lower activity levels), meaningful recovery of strength and function might occur in ~3–6 months, but the knee may never be fully stable for pivoting movements. PCL tear recovery can range widely. A minor PCL sprain treated without surgery might heal in 2–4 months with bracing and therapy, whereas a PCL tear that requires surgery will need a rehab similar to ACL – roughly 6–9 months before return to full activity. LCL tear recovery is often quicker if no surgery is needed – a mild LCL injury can heal in a 4–6 week period of rest and rehab, and a more moderate tear in a couple of months. If the LCL was surgically repaired or reconstructed, expect around 4–6 months of rehabilitation for a full recovery of strength and stability. In general, ACL injuries tend to keep athletes out the longest, while isolated PCL or LCL injuries (when treated conservatively) can sometimes return to normal function sooner. Regardless of the injury, dedicated physical therapy and gradual return to activity are crucial to rebuild stability and prevent re-injury.
Note: Without proper treatment, a torn knee ligament can lead to chronic instability and increase the risk of early osteoarthritis due to abnormal wear on the joint. Timely medical care and rehabilitation are essential to ensure the best long-term outcome for your knee.
Frequently Asked Questions (FAQs)
How can I tell if I tore my ACL, PCL, or LCL?
An ACL tear usually causes a loud pop at the moment of injury, with immediate swelling and instability (the knee may buckle right away). A PCL tear often has no pop and milder initial pain – instability might only be noticed during certain movements like going downstairs or decelerating because many PCL injuries are partial. An LCL tear produces pain on the outer side of the knee and the knee feels unstable if pushed inward (for example, after a blow to the inside of the knee). These clues can help, but a proper exam (with specific ligament tests and an MRI) is needed to know for sure which ligament is torn.
Is a PCL tear worse than an ACL tear?
Neither injury is good, but an ACL tear is generally considered more serious for athletes because it almost always causes complete ligament rupture and significant instability that often requires surgical reconstruction. A PCL tear is often less painful initially and more frequently a partial tear, which means many PCL injuries can be managed without surgery. In practical terms, a torn ACL can be more debilitating in the short term (with more immediate instability and difficulty with pivoting movements), whereas isolated PCL tears might allow more function. However, if a PCL tear is severe or combined with other injuries, it can be very serious as well. In summary, an ACL tear tends to have a bigger impact on knee stability (and usually needs surgical fix in active people), while a PCL tear can sometimes be “less bad” and heal with bracing – but each case should be evaluated individually.
Can PCL or LCL tears heal without surgery?
Yes – in many cases they can. Partial PCL tears often heal well with bracing and rehabilitation, and even some complete PCL tears can be managed without surgery if the knee remains stable. Likewise, partial LCL tears frequently heal on their own if the knee is properly braced for a few weeks. However, a fully torn LCL that leaves the knee very unstable (especially if it occurs along with other ligament injuries) usually requires surgical repair. In general, whether you need surgery depends on the severity of the tear and how stable your knee is after healing.
How long does it take to recover from ACL, PCL, or LCL tears?
ACL tears: If surgery is done (ACL reconstruction), expect about 9–12 months of rehabilitation to return to competitive sports. If no surgery is needed, strength and basic function might come back in around 3–6 months, though some knee instability could persist. PCL tears: A minor PCL injury can heal in a few months (2–4 months) with bracing and therapy. If the PCL tear requires surgery, recovery is longer – roughly 6–9 months of rehab (similar to an ACL recovery timeline). LCL tears: A mild LCL sprain may heal in as little as 4–6 weeks, while a severe LCL tear or an LCL that was surgically repaired might take on the order of 4–6 months to fully rehabilitate. Remember, these are approximate timelines – actual recovery varies depending on the person’s age, overall health, and whether other knee structures were injured.