Knee injuries are among the most common concerns for active individuals, athletes, and even people with a sudden fall or road accident. Among the many knee ligament injuries, ACL (Anterior Cruciate Ligament) tears and PCL (Posterior Cruciate Ligament) injuries are the most significant because they directly affect joint stability. Although both injuries involve major stabilising ligaments of the knee, their symptoms, mechanisms of injury, and progression are distinct.

In this blog, we will discuss the top 10 symptoms of ACL tear vs PCL injury, helping you understand the key differences so you can seek proper treatment without delay.

What Are ACL and PCL?

Before diving into symptoms, it’s helpful to understand the role of these two ligaments:

ACL (Anterior Cruciate Ligament)

Located in the centre of the knee. Prevents the shinbone (tibia) from sliding forward. Provides rotational stability during movements like pivoting, turning, and jumping.

PCL (Posterior Cruciate Ligament)

Positioned behind the ACL. Prevents the tibia from moving backwards. Important for stability when walking downhill, decelerating, or bending the knee.

Because these ligaments control opposite types of movements, their injuries present differently.

Top 10 Symptoms of ACL Tear vs PCL Injury

Below is a clear comparison of the symptoms associated with ACL tears and PCL injuries, along with explanations that will help you identify which ligament may be affected.

1. The Moment of Injury: “Pop” vs “No Pop”

ACL Tear

Most people describe hearing or feeling a loud “pop” at the moment of injury. This is one of the most important characteristic signs of an ACL tear.

Why does it happen? The ACL is under tension during sudden twisting or pivoting movements. When it ruptures, the snap is audible.

PCL Injury

A PCL injury generally does not produce a pop. Instead, people feel a deep, dull pain immediately after the impact.

Typical cause: A sudden force is applied to the front of the knee, such as during a fall on a bent knee or a dashboard injury in a car accident.

2. Immediate Knee Stability

ACL Tear - High Instability People often say the knee “gave way” instantly. It becomes difficult to continue playing a sport or even walk steadily.

PCL Injury - Mild to Moderate Instability PCL injuries typically produce less dramatic instability initially. Many can still stand or walk right after the injury, but feel discomfort when bending the knee.

3. Level of Swelling

ACL Tear – Swelling Within Hours ACL tears cause rapid, significant swelling, usually within 2–3 hours. Reason: Blood quickly fills the joint space due to rupture of ligament vessels.

PCL Injury – Swelling Comes Slowly Swelling is gradual and mild. Sometimes it appears 24 hours later. Reason: PCL tears cause deeper internal injury, so fluid buildup is slower.

4. Location of Pain

ACL Tear – Pain in the Centre or Front of Knee Pain is felt: Inside the knee joint Around the front During pivoting or quick turns Rotational movements worsen pain significantly.

PCL Injury – Pain at the Back of the Knee Pain is mainly felt: At the back of the knee Under the knee crease During kneeling or bending

5. Walking Pattern After Injury

ACL Tear – Difficulty Bearing Weight Walking feels unstable, particularly on uneven surfaces or while turning. The knee may buckle without warning.

PCL Injury – Walking Possible but Uncomfortable You can still walk in a straight line initially. Pain increases when: Walking downhill Descending stairs Squatting These activities push the tibia backwards, something a damaged PCL cannot control.

6. Range of Motion Issues

ACL Tear – Trouble Straightening the Knee The swelling and internal bleeding restrict normal extension. People often stand with their knees slightly bent.

PCL Injury – Trouble Bending the Knee The posterior pain becomes more noticeable when trying to kneel or bend deeply.

7. Sense of “Shift” vs “Sag”

ACL Tear – Knee Feels Like It Shifts Forward A feeling of: The knee sliding Sharp instability during turns Lack of rotational control This shifting sensation is especially noticeable when jogging or changing direction.

PCL Injury – “Posterior Sag” The tibia sags backwards when the knee is bent, a hallmark sign of PCL damage. This is often visible during a clinical exam.

8. Bruising Patterns

ACL Tear – Minimal External Bruising Because the bleeding stays inside the joint, visible bruising is usually limited.

PCL Injury – Bruising at the Back of the Knee Because the injury occurs deeper and near soft tissue structures, external bruising may appear behind the knee.

9. Ability to Continue Activity

ACL Tear – Usually Stops Activity Immediately Most athletes cannot continue playing. The knee feels too unstable and painful.

PCL Injury – Activity Sometimes Continues Some people even finish the game before noticing something is wrong. Symptoms escalate later as swelling and posterior pain increase.

10. Long-Term Symptoms if Untreated

ACL Tear – Chronic Instability Delayed treatment can lead to: Frequent knee buckling Meniscus tears Early osteoarthritis Rotational instability

PCL Injury – Difficulty With Deceleration Movements Untreated PCL injuries can cause: Pain when going downhill Weakness during squats Progressive knee wear on the inner (medial) side Subtle but persistent instability

Common Causes of ACL vs PCL Injuries

Understanding how these injuries occur can help in early recognition.

ACL Tear Mechanisms

Sudden pivoting during sports Landing awkwardly after a jump Rapid deceleration Changing direction quickly Collision causing knee rotation

PCL Injury Mechanisms

Falling directly on a bent knee Car accidents (dashboard hitting the shin) Hyperflexion injuries Direct blow to the front of the knee

Is It ACL or PCL?

Symptom ACL Tear PCL Injury Pop sound Common Rare Bruising Rare Back of the knee Swelling Fast Slow Walking Unstable Possible but painful Common cause Pivot, jump Fall on a bent knee Motion affected Straightening Bending Instability type Forward shift Backward sag Pain location Front/Pivot Back/Bend

When Should You Consult a Specialist?

Seek medical evaluation immediately if you experience:

• A pop with sudden knee collapse
• Difficulty bearing weight
• Rapid swelling
• Severe pain at the front or back of the knee
• Sensation of instability during walking

Early diagnosis is crucial because some ligament injuries worsen over time or lead to secondary damage like meniscus tears.

Diagnosis: What to Expect at the Clinic

A knee specialist typically performs:

• Detailed physical examination
• Stability tests (Lachman, Pivot Shift, Posterior Drawer)
• X-rays to rule out fractures
• MRI to confirm ligament tears

The accuracy of diagnosis depends heavily on clinical skills and imaging.

Treatment Approach: ACL vs PCL

While treatment details differ according to the patient and surgeon, the general plan includes:

ACL Tear Minor tears: Physiotherapy and bracing Complete tears: Often need surgical reconstruction, especially in active individuals

PCL Injury Grade 1–2: Usually treated with physiotherapy Grade 3: Surgery recommended if instability persists

Why Early Detection Matters

Delaying treatment can cause: Chronic instability Compensatory walking patterns Cartilage and meniscus damage Early arthritis

Timely evaluation helps protect long-term knee health and restore mobility faster.

Final Thoughts

Understanding the top 10 symptoms of ACL tear vs PCL injury can make a crucial difference in how quickly you recognise the injury and seek the right care. Although both these ligaments control essential aspects of knee stability, their symptoms are distinct enough for early identification.

If you or someone you know experiences persistent knee instability, pain, or difficulty with everyday movements, consulting an orthopaedic specialist ensures a timely diagnosis and appropriate treatment. Early action prevents long-term damage and keeps your knee functioning safely and efficiently.